src/eric7/Plugins/CheckerPlugins/CodeStyleChecker/Miscellaneous/MiscellaneousChecker.py

# -*- coding: utf-8 -*-

# Copyright (c) 2015 - 2023 Detlev Offenbach <detlev@die-offenbachs.de>
#

"""
Module implementing a checker for miscellaneous checks.
"""

import ast
import builtins
import contextlib
import copy
import itertools
import re
import sys
import tokenize

from collections import defaultdict, namedtuple
from keyword import iskeyword
from string import Formatter

import AstUtilities

from .eradicate import Eradicator
from .MiscellaneousDefaults import MiscellaneousCheckerDefaultArgs


def composeCallPath(node):
    """
    Generator function to assemble the call path of a given node.

    @param node node to assemble call path for
    @type ast.Node
    @yield call path components
    @ytype str
    """
    if isinstance(node, ast.Attribute):
        yield from composeCallPath(node.value)
        yield node.attr
    elif isinstance(node, ast.Name):
        yield node.id


class MiscellaneousChecker:
    """
    Class implementing a checker for miscellaneous checks.
    """

    Codes = [
        ## Coding line
        "M101",
        "M102",
        ## Copyright
        "M111",
        "M112",
        ## Shadowed Builtins
        "M131",
        "M132",
        ## Comprehensions
        "M181",
        "M182",
        "M183",
        "M184",
        "M185",
        "M186",
        "M187",
        "M188",
        "M189",
        "M191",
        "M192",
        "M193",
        "M195",
        "M196",
        "M197",
        "M198",
        ## Dictionaries with sorted keys
        "M201",
        ## Naive datetime usage
        "M301",
        "M302",
        "M303",
        "M304",
        "M305",
        "M306",
        "M307",
        "M308",
        "M311",
        "M312",
        "M313",
        "M314",
        "M315",
        "M321",
        ## sys.version and sys.version_info usage
        "M401",
        "M402",
        "M403",
        "M411",
        "M412",
        "M413",
        "M414",
        "M421",
        "M422",
        "M423",
        ## Bugbear
        "M501",
        "M502",
        "M503",
        "M504",
        "M505",
        "M507",
        "M509",
        "M510",
        "M511",
        "M512",
        "M513",
        "M514",
        "M515",
        "M516",
        "M517",
        "M518",
        "M519",
        "M520",
        "M521",
        "M522",
        "M523",
        "M524",
        "M525",
        "M526",
        "M527",
        ## Bugbear++
        "M581",
        "M582",
        ## Format Strings
        "M601",
        "M611",
        "M612",
        "M613",
        "M621",
        "M622",
        "M623",
        "M624",
        "M625",
        "M631",
        "M632",
        ## Logging
        "M651",
        "M652",
        "M653",
        "M654",
        "M655",
        ## Future statements
        "M701",
        "M702",
        ## Gettext
        "M711",
        ## print
        "M801",
        ## one element tuple
        "M811",
        ## Mutable Defaults
        "M821",
        "M822",
        ## return statements
        "M831",
        "M832",
        "M833",
        "M834",
        ## line continuation
        "M841",
        ## commented code
        "M891",
    ]

    Formatter = Formatter()
    FormatFieldRegex = re.compile(r"^((?:\s|.)*?)(\..*|\[.*\])?$")

    BuiltinsWhiteList = [
        "__name__",
        "__doc__",
        "credits",
    ]

    def __init__(self, source, filename, tree, select, ignore, expected, repeat, args):
        """
        Constructor

        @param source source code to be checked
        @type list of str
        @param filename name of the source file
        @type str
        @param tree AST tree of the source code
        @type ast.Module
        @param select list of selected codes
        @type list of str
        @param ignore list of codes to be ignored
        @type list of str
        @param expected list of expected codes
        @type list of str
        @param repeat flag indicating to report each occurrence of a code
        @type bool
        @param args dictionary of arguments for the miscellaneous checks
        @type dict
        """
        self.__select = tuple(select)
        self.__ignore = ("",) if select else tuple(ignore)
        self.__expected = expected[:]
        self.__repeat = repeat
        self.__filename = filename
        self.__source = source[:]
        self.__tree = copy.deepcopy(tree)
        self.__args = args

        self.__pep3101FormatRegex = re.compile(
            r'^(?:[^\'"]*[\'"][^\'"]*[\'"])*\s*%|^\s*%'
        )

        self.__builtins = [b for b in dir(builtins) if b not in self.BuiltinsWhiteList]

        self.__eradicator = Eradicator()

        # statistics counters
        self.counters = {}

        # collection of detected errors
        self.errors = []

        checkersWithCodes = [
            (self.__checkCoding, ("M101", "M102")),
            (self.__checkCopyright, ("M111", "M112")),
            (self.__checkBuiltins, ("M131", "M132")),
            (
                self.__checkComprehensions,
                (
                    "M181",
                    "M182",
                    "M183",
                    "M184",
                    "M185",
                    "M186",
                    "M187",
                    "M188",
                    "M189",
                    "M191",
                    "M192",
                    "M193",
                    "M195",
                    "M196",
                    "M197",
                    "M198",
                ),
            ),
            (self.__checkDictWithSortedKeys, ("M201",)),
            (
                self.__checkDateTime,
                (
                    "M301",
                    "M302",
                    "M303",
                    "M304",
                    "M305",
                    "M306",
                    "M307",
                    "M308",
                    "M311",
                    "M312",
                    "M313",
                    "M314",
                    "M315",
                    "M321",
                ),
            ),
            (
                self.__checkSysVersion,
                (
                    "M401",
                    "M402",
                    "M403",
                    "M411",
                    "M412",
                    "M413",
                    "M414",
                    "M421",
                    "M422",
                    "M423",
                ),
            ),
            (
                self.__checkBugBear,
                (
                    "M501",
                    "M502",
                    "M503",
                    "M504",
                    "M505",
                    "M507",
                    "M509",
                    "M510",
                    "M511",
                    "M512",
                    "M513",
                    "M514",
                    "M515",
                    "M516",
                    "M517",
                    "M518",
                    "M519",
                    "M520",
                    "M521",
                    "M522",
                    "M523",
                    "M524",
                    "M525",
                    "M526",
                    "M527",
                    "M581",
                    "M582",
                ),
            ),
            (self.__checkPep3101, ("M601",)),
            (
                self.__checkFormatString,
                (
                    "M611",
                    "M612",
                    "M613",
                    "M621",
                    "M622",
                    "M623",
                    "M624",
                    "M625",
                    "M631",
                    "M632",
                ),
            ),
            (self.__checkLogging, ("M651", "M652", "M653", "M654", "M655")),
            (self.__checkFuture, ("M701", "M702")),
            (self.__checkGettext, ("M711",)),
            (self.__checkPrintStatements, ("M801",)),
            (self.__checkTuple, ("M811",)),
            (self.__checkMutableDefault, ("M821", "M822")),
            (self.__checkReturn, ("M831", "M832", "M833", "M834")),
            (self.__checkLineContinuation, ("M841",)),
            (self.__checkCommentedCode, ("M891",)),
        ]

        # the eradicate whitelist
        commentedCodeCheckerArgs = self.__args.get(
            "CommentedCodeChecker",
            MiscellaneousCheckerDefaultArgs["CommentedCodeChecker"],
        )
        commentedCodeCheckerWhitelist = commentedCodeCheckerArgs.get(
            "WhiteList",
            MiscellaneousCheckerDefaultArgs["CommentedCodeChecker"]["WhiteList"],
        )
        self.__eradicator.update_whitelist(
            commentedCodeCheckerWhitelist, extend_default=False
        )

        self.__checkers = []
        for checker, codes in checkersWithCodes:
            if any(not (code and self.__ignoreCode(code)) for code in codes):
                self.__checkers.append(checker)

    def __ignoreCode(self, code):
        """
        Private method to check if the message code should be ignored.

        @param code message code to check for
        @type str
        @return flag indicating to ignore the given code
        @rtype bool
        """
        return code.startswith(self.__ignore) and not code.startswith(self.__select)

    def __error(self, lineNumber, offset, code, *args):
        """
        Private method to record an issue.

        @param lineNumber line number of the issue
        @type int
        @param offset position within line of the issue
        @type int
        @param code message code
        @type str
        @param args arguments for the message
        @type list
        """
        if self.__ignoreCode(code):
            return

        if code in self.counters:
            self.counters[code] += 1
        else:
            self.counters[code] = 1

        # Don't care about expected codes
        if code in self.__expected:
            return

        if code and (self.counters[code] == 1 or self.__repeat):
            # record the issue with one based line number
            self.errors.append(
                {
                    "file": self.__filename,
                    "line": lineNumber + 1,
                    "offset": offset,
                    "code": code,
                    "args": args,
                }
            )

    def run(self):
        """
        Public method to check the given source against miscellaneous
        conditions.
        """
        if not self.__filename:
            # don't do anything, if essential data is missing
            return

        if not self.__checkers:
            # don't do anything, if no codes were selected
            return

        for check in self.__checkers:
            check()

    def __getCoding(self):
        """
        Private method to get the defined coding of the source.

        @return tuple containing the line number and the coding
        @rtype tuple of int and str
        """
        for lineno, line in enumerate(self.__source[:5]):
            matched = re.search(r"coding[:=]\s*([-\w_.]+)", line, re.IGNORECASE)
            if matched:
                return lineno, matched.group(1)
        else:
            return 0, ""

    def __checkCoding(self):
        """
        Private method to check the presence of a coding line and valid
        encodings.
        """
        if len(self.__source) == 0:
            return

        encodings = [
            e.lower().strip()
            for e in self.__args.get(
                "CodingChecker", MiscellaneousCheckerDefaultArgs["CodingChecker"]
            ).split(",")
        ]
        lineno, coding = self.__getCoding()
        if coding:
            if coding.lower() not in encodings:
                self.__error(lineno, 0, "M102", coding)
        else:
            self.__error(0, 0, "M101")

    def __checkCopyright(self):
        """
        Private method to check the presence of a copyright statement.
        """
        source = "".join(self.__source)
        copyrightArgs = self.__args.get(
            "CopyrightChecker", MiscellaneousCheckerDefaultArgs["CopyrightChecker"]
        )
        copyrightMinFileSize = copyrightArgs.get(
            "MinFilesize",
            MiscellaneousCheckerDefaultArgs["CopyrightChecker"]["MinFilesize"],
        )
        copyrightAuthor = copyrightArgs.get(
            "Author", MiscellaneousCheckerDefaultArgs["CopyrightChecker"]["Author"]
        )
        copyrightRegexStr = (
            r"Copyright\s+(\(C\)\s+)?(\d{{4}}\s+-\s+)?\d{{4}}\s+{author}"
        )

        tocheck = max(1024, copyrightMinFileSize)
        topOfSource = source[:tocheck]
        if len(topOfSource) < copyrightMinFileSize:
            return

        copyrightRe = re.compile(copyrightRegexStr.format(author=r".*"), re.IGNORECASE)
        if not copyrightRe.search(topOfSource):
            self.__error(0, 0, "M111")
            return

        if copyrightAuthor:
            copyrightAuthorRe = re.compile(
                copyrightRegexStr.format(author=copyrightAuthor), re.IGNORECASE
            )
            if not copyrightAuthorRe.search(topOfSource):
                self.__error(0, 0, "M112")

    def __checkCommentedCode(self):
        """
        Private method to check for commented code.
        """
        source = "".join(self.__source)
        commentedCodeCheckerArgs = self.__args.get(
            "CommentedCodeChecker",
            MiscellaneousCheckerDefaultArgs["CommentedCodeChecker"],
        )
        aggressive = commentedCodeCheckerArgs.get(
            "Aggressive",
            MiscellaneousCheckerDefaultArgs["CommentedCodeChecker"]["Aggressive"],
        )
        for markedLine in self.__eradicator.commented_out_code_line_numbers(
            source, aggressive=aggressive
        ):
            self.__error(markedLine - 1, 0, "M891")

    def __checkLineContinuation(self):
        """
        Private method to check line continuation using backslash.
        """
        # generate source lines without comments
        linesIterator = iter(self.__source)
        tokens = tokenize.generate_tokens(lambda: next(linesIterator))
        comments = [token for token in tokens if token[0] == tokenize.COMMENT]
        stripped = self.__source[:]
        for comment in comments:
            lineno = comment[3][0]
            start = comment[2][1]
            stop = comment[3][1]
            content = stripped[lineno - 1]
            withoutComment = content[:start] + content[stop:]
            stripped[lineno - 1] = withoutComment.rstrip()

        # perform check with 'cleaned' source
        for lineIndex, line in enumerate(stripped):
            strippedLine = line.strip()
            if strippedLine.endswith("\\") and not strippedLine.startswith(
                ("assert", "with")
            ):
                self.__error(lineIndex, len(line), "M841")

    def __checkPrintStatements(self):
        """
        Private method to check for print statements.
        """
        for node in ast.walk(self.__tree):
            if (
                isinstance(node, ast.Call) and getattr(node.func, "id", None) == "print"
            ) or (hasattr(ast, "Print") and isinstance(node, ast.Print)):
                self.__error(node.lineno - 1, node.col_offset, "M801")

    def __checkTuple(self):
        """
        Private method to check for one element tuples.
        """
        for node in ast.walk(self.__tree):
            if isinstance(node, ast.Tuple) and len(node.elts) == 1:
                self.__error(node.lineno - 1, node.col_offset, "M811")

    def __checkFuture(self):
        """
        Private method to check the __future__ imports.
        """
        expectedImports = {
            i.strip()
            for i in self.__args.get("FutureChecker", "").split(",")
            if bool(i.strip())
        }
        if len(expectedImports) == 0:
            # nothing to check for; disabling the check
            return

        imports = set()
        node = None
        hasCode = False

        for node in ast.walk(self.__tree):
            if isinstance(node, ast.ImportFrom) and node.module == "__future__":
                imports |= {name.name for name in node.names}
            elif isinstance(node, ast.Expr):
                if not AstUtilities.isString(node.value):
                    hasCode = True
                    break
            elif not (AstUtilities.isString(node) or isinstance(node, ast.Module)):
                hasCode = True
                break

        if isinstance(node, ast.Module) or not hasCode:
            return

        if imports < expectedImports:
            if imports:
                self.__error(
                    node.lineno - 1,
                    node.col_offset,
                    "M701",
                    ", ".join(expectedImports),
                    ", ".join(imports),
                )
            else:
                self.__error(
                    node.lineno - 1, node.col_offset, "M702", ", ".join(expectedImports)
                )

    def __checkPep3101(self):
        """
        Private method to check for old style string formatting.
        """
        for lineno, line in enumerate(self.__source):
            match = self.__pep3101FormatRegex.search(line)
            if match:
                lineLen = len(line)
                pos = line.find("%")
                formatPos = pos
                formatter = "%"
                if line[pos + 1] == "(":
                    pos = line.find(")", pos)
                c = line[pos]
                while c not in "diouxXeEfFgGcrs":
                    pos += 1
                    if pos >= lineLen:
                        break
                    c = line[pos]
                if c in "diouxXeEfFgGcrs":
                    formatter += c
                self.__error(lineno, formatPos, "M601", formatter)

    def __checkFormatString(self):
        """
        Private method to check string format strings.
        """
        coding = self.__getCoding()[1]
        if not coding:
            # default to utf-8
            coding = "utf-8"

        visitor = TextVisitor()
        visitor.visit(self.__tree)
        for node in visitor.nodes:
            text = node.s
            if isinstance(text, bytes):
                try:
                    text = text.decode(coding)
                except UnicodeDecodeError:
                    continue
            fields, implicit, explicit = self.__getFields(text)
            if implicit:
                if node in visitor.calls:
                    self.__error(node.lineno - 1, node.col_offset, "M611")
                else:
                    if node.is_docstring:
                        self.__error(node.lineno - 1, node.col_offset, "M612")
                    else:
                        self.__error(node.lineno - 1, node.col_offset, "M613")

            if node in visitor.calls:
                call, strArgs = visitor.calls[node]

                numbers = set()
                names = set()
                # Determine which fields require a keyword and which an arg
                for name in fields:
                    fieldMatch = self.FormatFieldRegex.match(name)
                    try:
                        number = int(fieldMatch.group(1))
                    except ValueError:
                        number = -1
                    # negative numbers are considered keywords
                    if number >= 0:
                        numbers.add(number)
                    else:
                        names.add(fieldMatch.group(1))

                keywords = {keyword.arg for keyword in call.keywords}
                numArgs = len(call.args)
                if strArgs:
                    numArgs -= 1
                hasKwArgs = any(kw.arg is None for kw in call.keywords)
                hasStarArgs = sum(
                    1 for arg in call.args if isinstance(arg, ast.Starred)
                )

                if hasKwArgs:
                    keywords.discard(None)
                if hasStarArgs:
                    numArgs -= 1

                # if starargs or kwargs is not None, it can't count the
                # parameters but at least check if the args are used
                if hasKwArgs and not names:
                    # No names but kwargs
                    self.__error(call.lineno - 1, call.col_offset, "M623")
                if hasStarArgs and not numbers:
                    # No numbers but args
                    self.__error(call.lineno - 1, call.col_offset, "M624")

                if not hasKwArgs and not hasStarArgs:
                    # can actually verify numbers and names
                    for number in sorted(numbers):
                        if number >= numArgs:
                            self.__error(
                                call.lineno - 1, call.col_offset, "M621", number
                            )

                    for name in sorted(names):
                        if name not in keywords:
                            self.__error(call.lineno - 1, call.col_offset, "M622", name)

                for arg in range(numArgs):
                    if arg not in numbers:
                        self.__error(call.lineno - 1, call.col_offset, "M631", arg)

                for keyword in keywords:
                    if keyword not in names:
                        self.__error(call.lineno - 1, call.col_offset, "M632", keyword)

                if implicit and explicit:
                    self.__error(call.lineno - 1, call.col_offset, "M625")

    def __getFields(self, string):
        """
        Private method to extract the format field information.

        @param string format string to be parsed
        @type str
        @return format field information as a tuple with fields, implicit
            field definitions present and explicit field definitions present
        @rtype tuple of set of str, bool, bool
        """
        fields = set()
        cnt = itertools.count()
        implicit = False
        explicit = False
        try:
            for _literal, field, spec, conv in self.Formatter.parse(string):
                if field is not None and (conv is None or conv in "rsa"):
                    if not field:
                        field = str(next(cnt))
                        implicit = True
                    else:
                        explicit = True
                    fields.add(field)
                    fields.update(
                        parsedSpec[1]
                        for parsedSpec in self.Formatter.parse(spec)
                        if parsedSpec[1] is not None
                    )
        except ValueError:
            return set(), False, False
        else:
            return fields, implicit, explicit

    def __checkBuiltins(self):
        """
        Private method to check, if built-ins are shadowed.
        """
        functionDefs = [ast.FunctionDef]
        with contextlib.suppress(AttributeError):
            functionDefs.append(ast.AsyncFunctionDef)

        ignoreBuiltinAssignments = self.__args.get(
            "BuiltinsChecker", MiscellaneousCheckerDefaultArgs["BuiltinsChecker"]
        )

        for node in ast.walk(self.__tree):
            if isinstance(node, ast.Assign):
                # assign statement
                for element in node.targets:
                    if isinstance(element, ast.Name) and element.id in self.__builtins:
                        value = node.value
                        if (
                            isinstance(value, ast.Name)
                            and element.id in ignoreBuiltinAssignments
                            and value.id in ignoreBuiltinAssignments[element.id]
                        ):
                            # ignore compatibility assignments
                            continue
                        self.__error(
                            element.lineno - 1, element.col_offset, "M131", element.id
                        )
                    elif isinstance(element, (ast.Tuple, ast.List)):
                        for tupleElement in element.elts:
                            if (
                                isinstance(tupleElement, ast.Name)
                                and tupleElement.id in self.__builtins
                            ):
                                self.__error(
                                    tupleElement.lineno - 1,
                                    tupleElement.col_offset,
                                    "M131",
                                    tupleElement.id,
                                )
            elif isinstance(node, ast.For):
                # for loop
                target = node.target
                if isinstance(target, ast.Name) and target.id in self.__builtins:
                    self.__error(
                        target.lineno - 1, target.col_offset, "M131", target.id
                    )
                elif isinstance(target, (ast.Tuple, ast.List)):
                    for element in target.elts:
                        if (
                            isinstance(element, ast.Name)
                            and element.id in self.__builtins
                        ):
                            self.__error(
                                element.lineno - 1,
                                element.col_offset,
                                "M131",
                                element.id,
                            )
            elif any(isinstance(node, functionDef) for functionDef in functionDefs):
                # (asynchronous) function definition
                for arg in node.args.args:
                    if isinstance(arg, ast.arg) and arg.arg in self.__builtins:
                        self.__error(arg.lineno - 1, arg.col_offset, "M132", arg.arg)

    def __checkComprehensions(self):
        """
        Private method to check some comprehension related things.
        """
        for node in ast.walk(self.__tree):
            if isinstance(node, ast.Call) and isinstance(node.func, ast.Name):
                nArgs = len(node.args)
                nKwArgs = len(node.keywords)

                if (
                    nArgs == 1
                    and isinstance(node.args[0], ast.GeneratorExp)
                    and node.func.id in ("list", "set")
                ):
                    errorCode = {
                        "list": "M181",
                        "set": "M182",
                    }[node.func.id]
                    self.__error(node.lineno - 1, node.col_offset, errorCode)

                elif (
                    nArgs == 1
                    and isinstance(node.args[0], (ast.GeneratorExp, ast.ListComp))
                    and isinstance(node.args[0].elt, ast.Tuple)
                    and len(node.args[0].elt.elts) == 2
                    and node.func.id == "dict"
                ):
                    if isinstance(node.args[0], ast.GeneratorExp):
                        errorCode = "M183"
                    else:
                        errorCode = "M185"
                    self.__error(node.lineno - 1, node.col_offset, errorCode)

                elif (
                    nArgs == 1
                    and isinstance(node.args[0], ast.ListComp)
                    and node.func.id in ("list", "set")
                ):
                    errorCode = {
                        "list": "M195",
                        "set": "M184",
                    }[node.func.id]
                    self.__error(node.lineno - 1, node.col_offset, errorCode)

                elif nArgs == 1 and (
                    isinstance(node.args[0], ast.Tuple)
                    and node.func.id == "tuple"
                    or isinstance(node.args[0], ast.List)
                    and node.func.id == "list"
                ):
                    errorCode = {
                        "tuple": "M197",
                        "list": "M198",
                    }[node.func.id]
                    self.__error(
                        node.lineno - 1,
                        node.col_offset,
                        errorCode,
                        type(node.args[0]).__name__.lower(),
                        node.func.id,
                    )

                elif (
                    nArgs == 1
                    and isinstance(node.args[0], (ast.Tuple, ast.List))
                    and node.func.id in ("tuple", "list", "set", "dict")
                ):
                    errorCode = {
                        "tuple": "M192",
                        "list": "M193",
                        "set": "M191",
                        "dict": "M191",
                    }[node.func.id]
                    self.__error(
                        node.lineno - 1,
                        node.col_offset,
                        errorCode,
                        type(node.args[0]).__name__.lower(),
                        node.func.id,
                    )

                elif (
                    nArgs == 0
                    and not any(isinstance(a, ast.Starred) for a in node.args)
                    and not any(k.arg is None for k in node.keywords)
                    and node.func.id == "dict"
                ) or (
                    nArgs == 0 and nKwArgs == 0 and node.func.id in ("tuple", "list")
                ):
                    self.__error(node.lineno - 1, node.col_offset, "M186", node.func.id)

                elif (
                    node.func.id in {"list", "reversed"}
                    and nArgs > 0
                    and isinstance(node.args[0], ast.Call)
                    and isinstance(node.args[0].func, ast.Name)
                    and node.args[0].func.id == "sorted"
                ):
                    if node.func.id == "reversed":
                        reverseFlagValue = False
                        for kw in node.args[0].keywords:
                            if kw.arg != "reverse":
                                continue
                            if isinstance(kw.value, ast.NameConstant):
                                reverseFlagValue = kw.value.value
                            elif isinstance(kw.value, ast.Num):
                                reverseFlagValue = bool(kw.value.n)
                            else:
                                # Complex value
                                reverseFlagValue = None

                        if reverseFlagValue is None:
                            self.__error(
                                node.lineno - 1,
                                node.col_offset,
                                "M187a",
                                node.func.id,
                                node.args[0].func.id,
                            )
                        else:
                            self.__error(
                                node.lineno - 1,
                                node.col_offset,
                                "M187b",
                                node.func.id,
                                node.args[0].func.id,
                                not reverseFlagValue,
                            )
                    else:
                        self.__error(
                            node.lineno - 1,
                            node.col_offset,
                            "M187c",
                            node.func.id,
                            node.args[0].func.id,
                        )

                elif (
                    nArgs > 0
                    and isinstance(node.args[0], ast.Call)
                    and isinstance(node.args[0].func, ast.Name)
                    and (
                        (
                            node.func.id in {"set", "sorted"}
                            and node.args[0].func.id
                            in {"list", "reversed", "sorted", "tuple"}
                        )
                        or (
                            node.func.id in {"list", "tuple"}
                            and node.args[0].func.id in {"list", "tuple"}
                        )
                        or (node.func.id == "set" and node.args[0].func.id == "set")
                    )
                ):
                    self.__error(
                        node.lineno - 1,
                        node.col_offset,
                        "M188",
                        node.args[0].func.id,
                        node.func.id,
                    )

                elif (
                    node.func.id in {"reversed", "set", "sorted"}
                    and nArgs > 0
                    and isinstance(node.args[0], ast.Subscript)
                    and isinstance(node.args[0].slice, ast.Slice)
                    and node.args[0].slice.lower is None
                    and node.args[0].slice.upper is None
                    and isinstance(node.args[0].slice.step, ast.UnaryOp)
                    and isinstance(node.args[0].slice.step.op, ast.USub)
                    and isinstance(node.args[0].slice.step.operand, ast.Num)
                    and node.args[0].slice.step.operand.n == 1
                ):
                    self.__error(node.lineno - 1, node.col_offset, "M189", node.func.id)

                elif isinstance(node, (ast.ListComp, ast.SetComp)) and (
                    len(node.generators) == 1
                    and not node.generators[0].ifs
                    and not node.generators[0].is_async
                    and (
                        isinstance(node.elt, ast.Name)
                        and isinstance(node.generators[0].target, ast.Name)
                        and node.elt.id == node.generators[0].target.id
                    )
                ):
                    compType = {
                        ast.DictComp: "dict",
                        ast.ListComp: "list",
                        ast.SetComp: "set",
                    }[node.__class__]

                    self.__error(node.lineno - 1, node.col_offset, "M196", compType)

    def __checkMutableDefault(self):
        """
        Private method to check for use of mutable types as default arguments.
        """
        mutableTypes = (
            ast.Call,
            ast.Dict,
            ast.List,
            ast.Set,
            ast.DictComp,
            ast.ListComp,
            ast.SetComp,
        )
        mutableCalls = (
            "Counter",
            "OrderedDict",
            "collections.Counter",
            "collections.OrderedDict",
            "collections.defaultdict",
            "collections.deque",
            "defaultdict",
            "deque",
            "dict",
            "list",
            "set",
        )
        immutableCalls = (
            "tuple",
            "frozenset",
            "types.MappingProxyType",
            "MappingProxyType",
            "re.compile",
            "operator.attrgetter",
            "operator.itemgetter",
            "operator.methodcaller",
            "attrgetter",
            "itemgetter",
            "methodcaller",
        )
        functionDefs = [ast.FunctionDef]
        with contextlib.suppress(AttributeError):
            functionDefs.append(ast.AsyncFunctionDef)

        for node in ast.walk(self.__tree):
            if any(isinstance(node, functionDef) for functionDef in functionDefs):
                defaults = node.args.defaults[:]
                with contextlib.suppress(AttributeError):
                    defaults += node.args.kw_defaults[:]
                for default in defaults:
                    if any(
                        isinstance(default, mutableType) for mutableType in mutableTypes
                    ):
                        typeName = type(default).__name__
                        if isinstance(default, ast.Call):
                            callPath = ".".join(composeCallPath(default.func))
                            if callPath in mutableCalls:
                                self.__error(
                                    default.lineno - 1,
                                    default.col_offset,
                                    "M823",
                                    callPath + "()",
                                )
                            elif callPath not in immutableCalls:
                                self.__error(
                                    default.lineno - 1,
                                    default.col_offset,
                                    "M822",
                                    typeName,
                                )
                        else:
                            self.__error(
                                default.lineno - 1, default.col_offset, "M821", typeName
                            )

    def __dictShouldBeChecked(self, node):
        """
        Private function to test, if the node should be checked.

        @param node reference to the AST node
        @return flag indicating to check the node
        @rtype bool
        """
        if not all(AstUtilities.isString(key) for key in node.keys):
            return False

        if (
            "__IGNORE_WARNING__" in self.__source[node.lineno - 1]
            or "__IGNORE_WARNING_M201__" in self.__source[node.lineno - 1]
        ):
            return False

        lineNumbers = [key.lineno for key in node.keys]
        return len(lineNumbers) == len(set(lineNumbers))

    def __checkDictWithSortedKeys(self):
        """
        Private method to check, if dictionary keys appear in sorted order.
        """
        for node in ast.walk(self.__tree):
            if isinstance(node, ast.Dict) and self.__dictShouldBeChecked(node):
                for key1, key2 in zip(node.keys, node.keys[1:]):
                    if key2.s < key1.s:
                        self.__error(
                            key2.lineno - 1, key2.col_offset, "M201", key2.s, key1.s
                        )

    def __checkLogging(self):
        """
        Private method to check logging statements.
        """
        visitor = LoggingVisitor()
        visitor.visit(self.__tree)
        for node, reason in visitor.violations:
            self.__error(node.lineno - 1, node.col_offset, reason)

    def __checkGettext(self):
        """
        Private method to check the 'gettext' import statement.
        """
        for node in ast.walk(self.__tree):
            if isinstance(node, ast.ImportFrom) and any(
                name.asname == "_" for name in node.names
            ):
                self.__error(
                    node.lineno - 1, node.col_offset, "M711", node.names[0].name
                )

    def __checkBugBear(self):
        """
        Private method for bugbear checks.
        """
        visitor = BugBearVisitor()
        visitor.visit(self.__tree)
        for violation in visitor.violations:
            node = violation[0]
            reason = violation[1]
            params = violation[2:]
            self.__error(node.lineno - 1, node.col_offset, reason, *params)

    def __checkReturn(self):
        """
        Private method to check return statements.
        """
        visitor = ReturnVisitor()
        visitor.visit(self.__tree)
        for violation in visitor.violations:
            node = violation[0]
            reason = violation[1]
            self.__error(node.lineno - 1, node.col_offset, reason)

    def __checkDateTime(self):
        """
        Private method to check use of naive datetime functions.
        """
        # step 1: generate an augmented node tree containing parent info
        #         for each child node
        tree = copy.deepcopy(self.__tree)
        for node in ast.walk(tree):
            for childNode in ast.iter_child_nodes(node):
                childNode._dtCheckerParent = node

        # step 2: perform checks and report issues
        visitor = DateTimeVisitor()
        visitor.visit(tree)
        for violation in visitor.violations:
            node = violation[0]
            reason = violation[1]
            self.__error(node.lineno - 1, node.col_offset, reason)

    def __checkSysVersion(self):
        """
        Private method to check the use of sys.version and sys.version_info.
        """
        visitor = SysVersionVisitor()
        visitor.visit(self.__tree)
        for violation in visitor.violations:
            node = violation[0]
            reason = violation[1]
            self.__error(node.lineno - 1, node.col_offset, reason)


class TextVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor for bytes and str instances.

    It tries to detect docstrings as string of the first expression of each
    module, class or function.
    """

    # modeled after the string format flake8 extension

    def __init__(self):
        """
        Constructor
        """
        super().__init__()
        self.nodes = []
        self.calls = {}

    def __addNode(self, node):
        """
        Private method to add a node to our list of nodes.

        @param node reference to the node to add
        @type ast.AST
        """
        if not hasattr(node, "is_docstring"):
            node.is_docstring = False
        self.nodes.append(node)

    def visit_Str(self, node):
        """
        Public method to record a string node.

        @param node reference to the string node
        @type ast.Str
        """
        self.__addNode(node)

    def visit_Bytes(self, node):
        """
        Public method to record a bytes node.

        @param node reference to the bytes node
        @type ast.Bytes
        """
        self.__addNode(node)

    def visit_Constant(self, node):
        """
        Public method to handle constant nodes.

        @param node reference to the bytes node
        @type ast.Constant
        """
        if sys.version_info >= (3, 8, 0):
            if AstUtilities.isBaseString(node):
                self.__addNode(node)
            else:
                super().generic_visit(node)
        else:
            super().generic_visit(node)

    def __visitDefinition(self, node):
        """
        Private method handling class and function definitions.

        @param node reference to the node to handle
        @type ast.FunctionDef, ast.AsyncFunctionDef or ast.ClassDef
        """
        # Manually traverse class or function definition
        # * Handle decorators normally
        # * Use special check for body content
        # * Don't handle the rest (e.g. bases)
        for decorator in node.decorator_list:
            self.visit(decorator)
        self.__visitBody(node)

    def __visitBody(self, node):
        """
        Private method to traverse the body of the node manually.

        If the first node is an expression which contains a string or bytes it
        marks that as a docstring.

        @param node reference to the node to traverse
        @type ast.AST
        """
        if (
            node.body
            and isinstance(node.body[0], ast.Expr)
            and AstUtilities.isBaseString(node.body[0].value)
        ):
            node.body[0].value.is_docstring = True

        for subnode in node.body:
            self.visit(subnode)

    def visit_Module(self, node):
        """
        Public method to handle a module.

        @param node reference to the node to handle
        @type ast.Module
        """
        self.__visitBody(node)

    def visit_ClassDef(self, node):
        """
        Public method to handle a class definition.

        @param node reference to the node to handle
        @type ast.ClassDef
        """
        # Skipped nodes: ('name', 'bases', 'keywords', 'starargs', 'kwargs')
        self.__visitDefinition(node)

    def visit_FunctionDef(self, node):
        """
        Public method to handle a function definition.

        @param node reference to the node to handle
        @type ast.FunctionDef
        """
        # Skipped nodes: ('name', 'args', 'returns')
        self.__visitDefinition(node)

    def visit_AsyncFunctionDef(self, node):
        """
        Public method to handle an asynchronous function definition.

        @param node reference to the node to handle
        @type ast.AsyncFunctionDef
        """
        # Skipped nodes: ('name', 'args', 'returns')
        self.__visitDefinition(node)

    def visit_Call(self, node):
        """
        Public method to handle a function call.

        @param node reference to the node to handle
        @type ast.Call
        """
        if isinstance(node.func, ast.Attribute) and node.func.attr == "format":
            if AstUtilities.isBaseString(node.func.value):
                self.calls[node.func.value] = (node, False)
            elif (
                isinstance(node.func.value, ast.Name)
                and node.func.value.id == "str"
                and node.args
                and AstUtilities.isBaseString(node.args[0])
            ):
                self.calls[node.args[0]] = (node, True)
        super().generic_visit(node)


class LoggingVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check logging statements.
    """

    LoggingLevels = {
        "debug",
        "critical",
        "error",
        "info",
        "warn",
        "warning",
    }

    def __init__(self):
        """
        Constructor
        """
        super().__init__()

        self.__currentLoggingCall = None
        self.__currentLoggingArgument = None
        self.__currentLoggingLevel = None
        self.__currentExtraKeyword = None
        self.violations = []

    def __withinLoggingStatement(self):
        """
        Private method to check, if we are inside a logging statement.

        @return flag indicating we are inside a logging statement
        @rtype bool
        """
        return self.__currentLoggingCall is not None

    def __withinLoggingArgument(self):
        """
        Private method to check, if we are inside a logging argument.

        @return flag indicating we are inside a logging argument
        @rtype bool
        """
        return self.__currentLoggingArgument is not None

    def __withinExtraKeyword(self, node):
        """
        Private method to check, if we are inside the extra keyword.

        @param node reference to the node to be checked
        @type ast.keyword
        @return flag indicating we are inside the extra keyword
        @rtype bool
        """
        return (
            self.__currentExtraKeyword is not None
            and self.__currentExtraKeyword != node
        )

    def __detectLoggingLevel(self, node):
        """
        Private method to decide whether an AST Call is a logging call.

        @param node reference to the node to be processed
        @type ast.Call
        @return logging level
        @rtype str or None
        """
        with contextlib.suppress(AttributeError):
            if node.func.value.id == "warnings":
                return None

            if node.func.attr in LoggingVisitor.LoggingLevels:
                return node.func.attr

        return None

    def __isFormatCall(self, node):
        """
        Private method to check if a function call uses format.

        @param node reference to the node to be processed
        @type ast.Call
        @return flag indicating the function call uses format
        @rtype bool
        """
        try:
            return node.func.attr == "format"
        except AttributeError:
            return False

    def visit_Call(self, node):
        """
        Public method to handle a function call.

        Every logging statement and string format is expected to be a function
        call.

        @param node reference to the node to be processed
        @type ast.Call
        """
        # we are in a logging statement
        if (
            self.__withinLoggingStatement()
            and self.__withinLoggingArgument()
            and self.__isFormatCall(node)
        ):
            self.violations.append((node, "M651"))
            super().generic_visit(node)
            return

        loggingLevel = self.__detectLoggingLevel(node)

        if loggingLevel and self.__currentLoggingLevel is None:
            self.__currentLoggingLevel = loggingLevel

        # we are in some other statement
        if loggingLevel is None:
            super().generic_visit(node)
            return

        # we are entering a new logging statement
        self.__currentLoggingCall = node

        if loggingLevel == "warn":
            self.violations.append((node, "M655"))

        for index, child in enumerate(ast.iter_child_nodes(node)):
            if index == 1:
                self.__currentLoggingArgument = child
            if index > 1 and isinstance(child, ast.keyword) and child.arg == "extra":
                self.__currentExtraKeyword = child

            super().visit(child)

            self.__currentLoggingArgument = None
            self.__currentExtraKeyword = None

        self.__currentLoggingCall = None
        self.__currentLoggingLevel = None

    def visit_BinOp(self, node):
        """
        Public method to handle binary operations while processing the first
        logging argument.

        @param node reference to the node to be processed
        @type ast.BinOp
        """
        if self.__withinLoggingStatement() and self.__withinLoggingArgument():
            # handle percent format
            if isinstance(node.op, ast.Mod):
                self.violations.append((node, "M652"))

            # handle string concat
            if isinstance(node.op, ast.Add):
                self.violations.append((node, "M653"))

        super().generic_visit(node)

    def visit_JoinedStr(self, node):
        """
        Public method to handle f-string arguments.

        @param node reference to the node to be processed
        @type ast.JoinedStr
        """
        if (
            self.__withinLoggingStatement()
            and any(isinstance(i, ast.FormattedValue) for i in node.values)
            and self.__withinLoggingArgument()
        ):
            self.violations.append((node, "M654"))

            super().generic_visit(node)


BugBearContext = namedtuple("BugBearContext", ["node", "stack"])


class BugBearVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check for various topics.
    """

    #
    # This class was implemented along the BugBear flake8 extension (v 22.12.6).
    # Original: Copyright (c) 2016 Łukasz Langa
    #

    CONTEXTFUL_NODES = (
        ast.Module,
        ast.ClassDef,
        ast.AsyncFunctionDef,
        ast.FunctionDef,
        ast.Lambda,
        ast.ListComp,
        ast.SetComp,
        ast.DictComp,
        ast.GeneratorExp,
    )

    FUNCTION_NODES = (
        ast.AsyncFunctionDef,
        ast.FunctionDef,
        ast.Lambda,
    )

    NodeWindowSize = 4

    def __init__(self):
        """
        Constructor
        """
        super().__init__()

        self.nodeWindow = []
        self.violations = []
        self.contexts = []

        self.__M523Seen = set()

    @property
    def nodeStack(self):
        """
        Public method to get a reference to the most recent node stack.

        @return reference to the most recent node stack
        @rtype list
        """
        if len(self.contexts) == 0:
            return []

        context, stack = self.contexts[-1]
        return stack

    def __isIdentifier(self, arg):
        """
        Private method to check if arg is a valid identifier.

        See https://docs.python.org/2/reference/lexical_analysis.html#identifiers

        @param arg reference to an argument node
        @type ast.Node
        @return flag indicating a valid identifier
        @rtype TYPE
        """
        if not AstUtilities.isString(arg):
            return False

        return (
            re.match(r"^[A-Za-z_][A-Za-z0-9_]*$", AstUtilities.getValue(arg))
            is not None
        )

    def __composeCallPath(self, node):
        """
        Private method get the individual elements of the call path of a node.

        @param node reference to the node
        @type ast.Node
        @yield one element of the call path
        @ytype ast.Node
        """
        if isinstance(node, ast.Attribute):
            yield from self.__composeCallPath(node.value)
            yield node.attr
        elif isinstance(node, ast.Call):
            yield from self.__composeCallPath(node.func)
        elif isinstance(node, ast.Name):
            yield node.id

    def __toNameStr(self, node):
        """
        Private method to turn Name and Attribute nodes to strings, handling any
        depth of attribute accesses.


        @param node reference to the node
        @type ast.Name or ast.Attribute
        @return string representation
        @rtype str
        """
        if isinstance(node, ast.Name):
            return node.id

        if isinstance(node, ast.Call):
            return self.__toNameStr(node.func)

        try:
            return self.__toNameStr(node.value) + "." + node.attr
        except AttributeError:
            return self.__toNameStr(node.value)

    def __typesafeIssubclass(self, obj, classOrTuple):
        """
        Private method implementing a type safe issubclass() function.

        @param obj reference to the object to be tested
        @type any
        @param classOrTuple type to check against
        @type type
        @return flag indicating a subclass
        @rtype bool
        """
        try:
            return issubclass(obj, classOrTuple)
        except TypeError:
            # User code specifies a type that is not a type in our current run.
            # Might be their error, might be a difference in our environments.
            # We don't know so we ignore this.
            return False

    def __getAssignedNames(self, loopNode):
        """
        Private method to get the names of a for loop.

        @param loopNode reference to the node to be processed
        @type ast.For
        @yield DESCRIPTION
        @ytype TYPE
        """
        loopTargets = (ast.For, ast.AsyncFor, ast.comprehension)
        for node in self.__childrenInScope(loopNode):
            if isinstance(node, (ast.Assign)):
                for child in node.targets:
                    yield from self.__namesFromAssignments(child)
            if isinstance(node, loopTargets + (ast.AnnAssign, ast.AugAssign)):
                yield from self.__namesFromAssignments(node.target)

    def __namesFromAssignments(self, assignTarget):
        """
        Private method to get names of an assignment.

        @param assignTarget reference to the node to be processed
        @type ast.Node
        @yield name of the assignment
        @ytype str
        """
        if isinstance(assignTarget, ast.Name):
            yield assignTarget.id
        elif isinstance(assignTarget, ast.Starred):
            yield from self.__namesFromAssignments(assignTarget.value)
        elif isinstance(assignTarget, (ast.List, ast.Tuple)):
            for child in assignTarget.elts:
                yield from self.__namesFromAssignments(child)

    def __childrenInScope(self, node):
        """
        Private method to get all child nodes in the given scope.

        @param node reference to the node to be processed
        @type ast.Node
        @yield reference to a child node
        @ytype ast.Node
        """
        yield node
        if not isinstance(node, BugBearVisitor.FUNCTION_NODES):
            for child in ast.iter_child_nodes(node):
                yield from self.__childrenInScope(child)

    def visit(self, node):
        """
        Public method to traverse a given AST node.

        @param node AST node to be traversed
        @type ast.Node
        """
        isContextful = isinstance(node, BugBearVisitor.CONTEXTFUL_NODES)

        if isContextful:
            context = BugBearContext(node, [])
            self.contexts.append(context)

        self.nodeStack.append(node)
        self.nodeWindow.append(node)
        self.nodeWindow = self.nodeWindow[-BugBearVisitor.NodeWindowSize :]

        super().visit(node)

        self.nodeStack.pop()

        if isContextful:
            self.contexts.pop()

    def visit_ExceptHandler(self, node):
        """
        Public method to handle exception handlers.

        @param node reference to the node to be processed
        @type ast.ExceptHandler
        """
        redundantExceptions = {
            "OSError": {
                # All of these are actually aliases of OSError since Python 3.3
                "IOError",
                "EnvironmentError",
                "WindowsError",
                "mmap.error",
                "socket.error",
                "select.error",
            },
            "ValueError": {
                "binascii.Error",
            },
        }

        if node.type is None:
            # bare except is handled by pycodestyle already
            pass

        elif isinstance(node.type, ast.Tuple):
            names = [self.__toNameStr(e) for e in node.type.elts]
            as_ = " as " + node.name if node.name is not None else ""
            if len(names) == 0:
                self.violations.append((node, "M501", as_))
            elif len(names) == 1:
                self.violations.append((node, "M513", *names))
            else:
                # See if any of the given exception names could be removed, e.g. from:
                #  (MyError, MyError)  # duplicate names
                #  (MyError, BaseException)  # everything derives from the Base
                #  (Exception, TypeError)  # builtins where one subclasses another
                #  (IOError, OSError)  # IOError is an alias of OSError since Python3.3
                # but note that other cases are impractical to handle from the AST.
                # We expect this is mostly useful for users who do not have the
                # builtin exception hierarchy memorised, and include a 'shadowed'
                # subtype without realising that it's redundant.
                good = sorted(set(names), key=names.index)
                if "BaseException" in good:
                    good = ["BaseException"]
                # Remove redundant exceptions that the automatic system either handles
                # poorly (usually aliases) or can't be checked (e.g. it's not an
                # built-in exception).
                for primary, equivalents in redundantExceptions.items():
                    if primary in good:
                        good = [g for g in good if g not in equivalents]

                for name, other in itertools.permutations(tuple(good), 2):
                    if (
                        self.__typesafeIssubclass(
                            getattr(builtins, name, type), getattr(builtins, other, ())
                        )
                        and name in good
                    ):
                        good.remove(name)
                if good != names:
                    desc = (
                        good[0] if len(good) == 1 else "({0})".format(", ".join(good))
                    )
                    self.violations.append((node, "M514", ", ".join(names), as_, desc))

        self.generic_visit(node)

    def visit_UAdd(self, node):
        """
        Public method to handle unary additions.

        @param node reference to the node to be processed
        @type ast.UAdd
        """
        trailingNodes = list(map(type, self.nodeWindow[-4:]))
        if trailingNodes == [ast.UnaryOp, ast.UAdd, ast.UnaryOp, ast.UAdd]:
            originator = self.nodeWindow[-4]
            self.violations.append((originator, "M502"))

        self.generic_visit(node)

    def visit_Call(self, node):
        """
        Public method to handle a function call.

        @param node reference to the node to be processed
        @type ast.Call
        """
        if isinstance(node.func, ast.Attribute):
            self.__checkForM505(node)
        else:
            with contextlib.suppress(AttributeError, IndexError):
                # bad super() call
                if isinstance(node.func, ast.Name) and node.func.id == "super":
                    args = node.args
                    if (
                        len(args) == 2
                        and isinstance(args[0], ast.Attribute)
                        and isinstance(args[0].value, ast.Name)
                        and args[0].value.id == "self"
                        and args[0].attr == "__class__"
                    ):
                        self.violations.append((node, "M582"))

                # bad getattr and setattr
                if (
                    node.func.id in ("getattr", "hasattr")
                    and node.args[1].s == "__call__"
                ):
                    self.violations.append((node, "M504"))
                if (
                    node.func.id == "getattr"
                    and len(node.args) == 2
                    and self.__isIdentifier(node.args[1])
                    and iskeyword(AstUtilities.getValue(node.args[1]))
                ):
                    self.violations.append((node, "M509"))
                elif (
                    node.func.id == "setattr"
                    and len(node.args) == 3
                    and self.__isIdentifier(node.args[1])
                    and iskeyword(AstUtilities.getValue(node.args[1]))
                ):
                    self.violations.append((node, "M510"))

            self.__checkForM526(node)

        self.generic_visit(node)

    def visit_Assign(self, node):
        """
        Public method to handle assignments.

        @param node reference to the node to be processed
        @type ast.Assign
        """
        if len(node.targets) == 1:
            target = node.targets[0]
            if (
                isinstance(target, ast.Attribute)
                and isinstance(target.value, ast.Name)
                and (target.value.id, target.attr) == ("os", "environ")
            ):
                self.violations.append((node, "M503"))

        self.generic_visit(node)

    def visit_For(self, node):
        """
        Public method to handle 'for' statements.

        @param node reference to the node to be processed
        @type ast.For
        """
        self.__checkForM507(node)
        self.__checkForM520(node)
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_AsyncFor(self, node):
        """
        Public method to handle 'for' statements.

        @param node reference to the node to be processed
        @type ast.AsyncFor
        """
        self.__checkForM507(node)
        self.__checkForM520(node)
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_While(self, node):
        """
        Public method to handle 'while' statements.

        @param node reference to the node to be processed
        @type ast.While
        """
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_ListComp(self, node):
        """
        Public method to handle list comprehensions.

        @param node reference to the node to be processed
        @type ast.ListComp
        """
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_SetComp(self, node):
        """
        Public method to handle set comprehensions.

        @param node reference to the node to be processed
        @type ast.SetComp
        """
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_DictComp(self, node):
        """
        Public method to handle dictionary comprehensions.

        @param node reference to the node to be processed
        @type ast.DictComp
        """
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_GeneratorExp(self, node):
        """
        Public method to handle generator expressions.

        @param node reference to the node to be processed
        @type ast.GeneratorExp
        """
        self.__checkForM523(node)

        self.generic_visit(node)

    def visit_Assert(self, node):
        """
        Public method to handle 'assert' statements.

        @param node reference to the node to be processed
        @type ast.Assert
        """
        if (
            AstUtilities.isNameConstant(node.test)
            and AstUtilities.getValue(node.test) is False
        ):
            self.violations.append((node, "M511"))

        self.generic_visit(node)

    def visit_FunctionDef(self, node):
        """
        Public method to handle function definitions.

        @param node reference to the node to be processed
        @type ast.FunctionDef
        """
        self.__checkForM518(node)
        self.__checkForM519(node)
        self.__checkForM521(node)

        self.generic_visit(node)

    def visit_ClassDef(self, node):
        """
        Public method to handle class definitions.

        @param node reference to the node to be processed
        @type ast.ClassDef
        """
        self.__checkForM518(node)
        self.__checkForM521(node)
        self.__checkForM524AndM527(node)

        self.generic_visit(node)

    def visit_Try(self, node):
        """
        Public method to handle 'try' statements'.

        @param node reference to the node to be processed
        @type ast.Try
        """
        self.__checkForM512(node)
        self.__checkForM525(node)

        self.generic_visit(node)

    def visit_Compare(self, node):
        """
        Public method to handle comparison statements.

        @param node reference to the node to be processed
        @type ast.Compare
        """
        self.__checkForM515(node)

        self.generic_visit(node)

    def visit_Raise(self, node):
        """
        Public method to handle 'raise' statements.

        @param node reference to the node to be processed
        @type ast.Raise
        """
        self.__checkForM516(node)

        self.generic_visit(node)

    def visit_With(self, node):
        """
        Public method to handle 'with' statements.

        @param node reference to the node to be processed
        @type ast.With
        """
        self.__checkForM517(node)
        self.__checkForM522(node)

        self.generic_visit(node)

    def visit_JoinedStr(self, node):
        """
        Public method to handle f-string arguments.

        @param node reference to the node to be processed
        @type ast.JoinedStr
        """
        for value in node.values:
            if isinstance(value, ast.FormattedValue):
                return

        self.violations.append((node, "M581"))

    def __checkForM505(self, node):
        """
        Private method to check the use of *strip().

        @param node reference to the node to be processed
        @type ast.Call
        """
        if node.func.attr not in ("lstrip", "rstrip", "strip"):
            return  # method name doesn't match

        if len(node.args) != 1 or not AstUtilities.isString(node.args[0]):
            return  # used arguments don't match the builtin strip

        s = AstUtilities.getValue(node.args[0])
        if len(s) == 1:
            return  # stripping just one character

        if len(s) == len(set(s)):
            return  # no characters appear more than once

        self.violations.append((node, "M505"))

    def __checkForM507(self, node):
        """
        Private method to check for unused loop variables.

        @param node reference to the node to be processed
        @type ast.For or ast.AsyncFor
        """
        targets = NameFinder()
        targets.visit(node.target)
        ctrlNames = set(filter(lambda s: not s.startswith("_"), targets.getNames()))
        body = NameFinder()
        for expr in node.body:
            body.visit(expr)
        usedNames = set(body.getNames())
        for name in sorted(ctrlNames - usedNames):
            n = targets.getNames()[name][0]
            self.violations.append((n, "M507", name))

    def __checkForM512(self, node):
        """
        Private method to check for return/continue/break inside finally blocks.

        @param node reference to the node to be processed
        @type ast.Try
        """

        def _loop(node, badNodeTypes):
            if isinstance(node, (ast.AsyncFunctionDef, ast.FunctionDef)):
                return

            if isinstance(node, (ast.While, ast.For)):
                badNodeTypes = (ast.Return,)

            elif isinstance(node, badNodeTypes):
                self.violations.append((node, "M512"))

            for child in ast.iter_child_nodes(node):
                _loop(child, badNodeTypes)

        for child in node.finalbody:
            _loop(child, (ast.Return, ast.Continue, ast.Break))

    def __checkForM515(self, node):
        """
        Private method to check for pointless comparisons.

        @param node reference to the node to be processed
        @type ast.Compare
        """
        if isinstance(self.nodeStack[-2], ast.Expr):
            self.violations.append((node, "M515"))

    def __checkForM516(self, node):
        """
        Private method to check for raising a literal instead of an exception.

        @param node reference to the node to be processed
        @type ast.Raise
        """
        if (
            AstUtilities.isNameConstant(node.exc)
            or AstUtilities.isNumber(node.exc)
            or AstUtilities.isString(node.exc)
        ):
            self.violations.append((node, "M516"))

    def __checkForM517(self, node):
        """
        Private method to check for use of the evil syntax
        'with assertRaises(Exception):.

        @param node reference to the node to be processed
        @type ast.With
        """
        item = node.items[0]
        itemContext = item.context_expr
        if (
            hasattr(itemContext, "func")
            and hasattr(itemContext.func, "attr")
            and itemContext.func.attr == "assertRaises"
            and len(itemContext.args) == 1
            and isinstance(itemContext.args[0], ast.Name)
            and itemContext.args[0].id == "Exception"
            and not item.optional_vars
        ):
            self.violations.append((node, "M517"))

    def __checkForM518(self, node):
        """
        Private method to check for useless expressions.

        @param node reference to the node to be processed
        @type ast.FunctionDef
        """
        subnodeClasses = (
            (
                ast.Constant,
                ast.List,
                ast.Set,
                ast.Dict,
            )
            if sys.version_info >= (3, 8, 0)
            else (
                ast.Num,
                ast.Bytes,
                ast.NameConstant,
                ast.List,
                ast.Set,
                ast.Dict,
            )
        )
        for subnode in node.body:
            if not isinstance(subnode, ast.Expr):
                continue

            if isinstance(subnode.value, subnodeClasses) and not AstUtilities.isString(
                subnode.value
            ):
                self.violations.append((subnode, "M518"))

    def __checkForM519(self, node):
        """
        Private method to check for use of 'functools.lru_cache' or 'functools.cache'.

        @param node reference to the node to be processed
        @type ast.FunctionDef
        """
        caches = {
            "functools.cache",
            "functools.lru_cache",
            "cache",
            "lru_cache",
        }

        if (
            len(node.decorator_list) == 0
            or len(self.contexts) < 2
            or not isinstance(self.contexts[-2].node, ast.ClassDef)
        ):
            return

        # Preserve decorator order so we can get the lineno from the decorator node
        # rather than the function node (this location definition changes in Python 3.8)
        resolvedDecorators = (
            ".".join(self.__composeCallPath(decorator))
            for decorator in node.decorator_list
        )
        for idx, decorator in enumerate(resolvedDecorators):
            if decorator in {"classmethod", "staticmethod"}:
                return

            if decorator in caches:
                self.violations.append((node.decorator_list[idx], "M519"))
                return

    def __checkForM520(self, node):
        """
        Private method to check for a loop that modifies its iterable.

        @param node reference to the node to be processed
        @type ast.For or ast.AsyncFor
        """
        targets = NameFinder()
        targets.visit(node.target)
        ctrlNames = set(targets.getNames())

        iterset = M520NameFinder()
        iterset.visit(node.iter)
        itersetNames = set(iterset.getNames())

        for name in sorted(ctrlNames):
            if name in itersetNames:
                n = targets.getNames()[name][0]
                self.violations.append((n, "M520"))

    def __checkForM521(self, node):
        """
        Private method to check for use of an f-string as docstring.

        @param node reference to the node to be processed
        @type ast.FunctionDef or ast.ClassDef
        """
        if (
            node.body
            and isinstance(node.body[0], ast.Expr)
            and isinstance(node.body[0].value, ast.JoinedStr)
        ):
            self.violations.append((node.body[0].value, "M521"))

    def __checkForM522(self, node):
        """
        Private method to check for use of an f-string as docstring.

        @param node reference to the node to be processed
        @type ast.With
        """
        item = node.items[0]
        itemContext = item.context_expr
        if (
            hasattr(itemContext, "func")
            and hasattr(itemContext.func, "value")
            and hasattr(itemContext.func.value, "id")
            and itemContext.func.value.id == "contextlib"
            and hasattr(itemContext.func, "attr")
            and itemContext.func.attr == "suppress"
            and len(itemContext.args) == 0
        ):
            self.violations.append((node, "M522"))

    def __checkForM523(self, loopNode):
        """
        Private method to check that functions (including lambdas) do not use loop
        variables.

        @param loopNode reference to the node to be processed
        @type ast.For, ast.AsyncFor, ast.While, ast.ListComp, ast.SetComp,ast.DictComp,
            or ast.GeneratorExp
        """
        safe_functions = []
        suspiciousVariables = []
        for node in ast.walk(loopNode):
            # check if function is immediately consumed to avoid false alarm
            if isinstance(node, ast.Call):
                # check for filter&reduce
                if (
                    isinstance(node.func, ast.Name)
                    and node.func.id in ("filter", "reduce", "map")
                ) or (
                    isinstance(node.func, ast.Attribute)
                    and node.func.attr == "reduce"
                    and isinstance(node.func.value, ast.Name)
                    and node.func.value.id == "functools"
                ):
                    for arg in node.args:
                        if isinstance(arg, BugBearVisitor.FUNCTION_NODES):
                            safe_functions.append(arg)

                # check for key=
                for keyword in node.keywords:
                    if keyword.arg == "key" and isinstance(
                        keyword.value, BugBearVisitor.FUNCTION_NODES
                    ):
                        safe_functions.append(keyword.value)

            # mark `return lambda: x` as safe
            # does not (currently) check inner lambdas in a returned expression
            # e.g. `return (lambda: x, )
            if isinstance(node, ast.Return) and isinstance(
                node.value, BugBearVisitor.FUNCTION_NODES
            ):
                safe_functions.append(node.value)

            # find unsafe functions
            if (
                isinstance(node, BugBearVisitor.FUNCTION_NODES)
                and node not in safe_functions
            ):
                argnames = {
                    arg.arg for arg in ast.walk(node.args) if isinstance(arg, ast.arg)
                }
                if isinstance(node, ast.Lambda):
                    bodyNodes = ast.walk(node.body)
                else:
                    bodyNodes = itertools.chain.from_iterable(map(ast.walk, node.body))
                errors = []
                for name in bodyNodes:
                    if isinstance(name, ast.Name) and name.id not in argnames:
                        if isinstance(name.ctx, ast.Load):
                            errors.append((name.lineno, name.col_offset, name.id, name))
                        elif isinstance(name.ctx, ast.Store):
                            argnames.add(name.id)
                for err in errors:
                    if err[2] not in argnames and err not in self.__M523Seen:
                        self.__M523Seen.add(err)  # dedupe across nested loops
                        suspiciousVariables.append(err)

        if suspiciousVariables:
            reassignedInLoop = set(self.__getAssignedNames(loopNode))

        for err in sorted(suspiciousVariables):
            if reassignedInLoop.issuperset(err[2]):
                self.violations.append((err[3], "M523", err[2]))

    def __checkForM524AndM527(self, node):
        """
        Private method to check for inheritance from abstract classes in abc and lack of
        any methods decorated with abstract*.

        @param node reference to the node to be processed
        @type ast.ClassDef
        """  # __IGNORE_WARNING_D234r__

        def isAbcClass(value, name="ABC"):
            if isinstance(value, ast.keyword):
                return value.arg == "metaclass" and isAbcClass(value.value, "ABCMeta")

            # class foo(ABC)
            # class foo(abc.ABC)
            return (isinstance(value, ast.Name) and value.id == name) or (
                isinstance(value, ast.Attribute)
                and value.attr == name
                and isinstance(value.value, ast.Name)
                and value.value.id == "abc"
            )

        def isAbstractDecorator(expr):
            return (isinstance(expr, ast.Name) and expr.id[:8] == "abstract") or (
                isinstance(expr, ast.Attribute) and expr.attr[:8] == "abstract"
            )

        def isOverload(expr):
            return (isinstance(expr, ast.Name) and expr.id == "overload") or (
                isinstance(expr, ast.Attribute) and expr.attr == "overload"
            )

        def emptyBody(body):
            def isStrOrEllipsis(node):
                # ast.Ellipsis and ast.Str used in python<3.8
                return isinstance(node, (ast.Ellipsis, ast.Str)) or (
                    isinstance(node, ast.Constant)
                    and (node.value is Ellipsis or isinstance(node.value, str))
                )

            # Function body consist solely of `pass`, `...`, and/or (doc)string literals
            return all(
                isinstance(stmt, ast.Pass)
                or (isinstance(stmt, ast.Expr) and isStrOrEllipsis(stmt.value))
                for stmt in body
            )

        # don't check multiple inheritance
        if len(node.bases) + len(node.keywords) > 1:
            return

        # only check abstract classes
        if not any(map(isAbcClass, (*node.bases, *node.keywords))):
            return

        hasAbstractMethod = False

        if not any(map(isAbcClass, (*node.bases, *node.keywords))):
            return

        for stmt in node.body:
            # Ignore abc's that declares a class attribute that must be set
            if isinstance(stmt, (ast.AnnAssign, ast.Assign)):
                hasAbstractMethod = True
                continue

            # only check function defs
            if not isinstance(stmt, (ast.FunctionDef, ast.AsyncFunctionDef)):
                continue

            hasAbstractDecorator = any(map(isAbstractDecorator, stmt.decorator_list))

            hasAbstractMethod |= hasAbstractDecorator

            if (
                not hasAbstractDecorator
                and emptyBody(stmt.body)
                and not any(map(isOverload, stmt.decorator_list))
            ):
                self.violations.append((stmt, "M527", stmt.name))

        if not hasAbstractMethod:
            self.violations.append((node, "M524", node.name))

    def __checkForM525(self, node):
        """
        Private method to check for exceptions being handled multiple times.

        @param node reference to the node to be processed
        @type ast.Try
        """
        seen = []

        for handler in node.handlers:
            if isinstance(handler.type, (ast.Name, ast.Attribute)):
                name = ".".join(self.__composeCallPath(handler.type))
                seen.append(name)
            elif isinstance(handler.type, ast.Tuple):
                # to avoid checking the same as M514, remove duplicates per except
                uniques = set()
                for entry in handler.type.elts:
                    name = ".".join(self.__composeCallPath(entry))
                    uniques.add(name)
                seen.extend(uniques)

        # sort to have a deterministic output
        duplicates = sorted({x for x in seen if seen.count(x) > 1})
        for duplicate in duplicates:
            self.violations.append((node, "M525", duplicate))

    def __checkForM526(self, node):
        """
        Private method to check for Star-arg unpacking after keyword argument.

        @param node reference to the node to be processed
        @type ast.Call
        """
        if not node.keywords:
            return

        starreds = [arg for arg in node.args if isinstance(arg, ast.Starred)]
        if not starreds:
            return

        firstKeyword = node.keywords[0].value
        for starred in starreds:
            if (starred.lineno, starred.col_offset) > (
                firstKeyword.lineno,
                firstKeyword.col_offset,
            ):
                self.violations.append((node, "M526"))


class NameFinder(ast.NodeVisitor):
    """
    Class to extract a name out of a tree of nodes.
    """

    def __init__(self):
        """
        Constructor
        """
        super().__init__()

        self.__names = {}

    def visit_Name(self, node):
        """
        Public method to handle 'Name' nodes.

        @param node reference to the node to be processed
        @type ast.Name
        """
        self.__names.setdefault(node.id, []).append(node)

    def visit(self, node):
        """
        Public method to traverse a given AST node.

        @param node AST node to be traversed
        @type ast.Node
        @return reference to the last processed node
        @rtype ast.Node
        """
        if isinstance(node, list):
            for elem in node:
                super().visit(elem)
            return node
        else:
            return super().visit(node)

    def getNames(self):
        """
        Public method to return the extracted names and Name nodes.

        @return dictionary containing the names as keys and the list of nodes
        @rtype dict
        """
        return self.__names


class M520NameFinder(NameFinder):
    """
    Class to extract a name out of a tree of nodes ignoring names defined within the
    local scope of a comprehension.
    """

    def visit_GeneratorExp(self, node):
        """
        Public method to handle a generator expressions.

        @param node reference to the node to be processed
        @type ast.GeneratorExp
        """
        self.visit(node.generators)

    def visit_ListComp(self, node):
        """
        Public method  to handle a list comprehension.

        @param node reference to the node to be processed
        @type TYPE
        """
        self.visit(node.generators)

    def visit_DictComp(self, node):
        """
        Public method  to handle a dictionary comprehension.

        @param node reference to the node to be processed
        @type TYPE
        """
        self.visit(node.generators)

    def visit_comprehension(self, node):
        """
        Public method  to handle the 'for' of a comprehension.

        @param node reference to the node to be processed
        @type ast.comprehension
        """
        self.visit(node.iter)

    def visit_Lambda(self, node):
        """
        Public method  to handle a Lambda function.

        @param node reference to the node to be processed
        @type ast.Lambda
        """
        self.visit(node.body)
        for lambdaArg in node.args.args:
            self.getNames().pop(lambdaArg.arg, None)


class ReturnVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check return statements.
    """

    Assigns = "assigns"
    Refs = "refs"
    Returns = "returns"

    def __init__(self):
        """
        Constructor
        """
        super().__init__()

        self.__stack = []
        self.violations = []
        self.__loopCount = 0

    @property
    def assigns(self):
        """
        Public method to get the Assign nodes.

        @return dictionary containing the node name as key and line number
            as value
        @rtype dict
        """
        return self.__stack[-1][ReturnVisitor.Assigns]

    @property
    def refs(self):
        """
        Public method to get the References nodes.

        @return dictionary containing the node name as key and line number
            as value
        @rtype dict
        """
        return self.__stack[-1][ReturnVisitor.Refs]

    @property
    def returns(self):
        """
        Public method to get the Return nodes.

        @return dictionary containing the node name as key and line number
            as value
        @rtype dict
        """
        return self.__stack[-1][ReturnVisitor.Returns]

    def visit_For(self, node):
        """
        Public method to handle a for loop.

        @param node reference to the for node to handle
        @type ast.For
        """
        self.__visitLoop(node)

    def visit_AsyncFor(self, node):
        """
        Public method to handle an async for loop.

        @param node reference to the async for node to handle
        @type ast.AsyncFor
        """
        self.__visitLoop(node)

    def visit_While(self, node):
        """
        Public method to handle a while loop.

        @param node reference to the while node to handle
        @type ast.While
        """
        self.__visitLoop(node)

    def __visitLoop(self, node):
        """
        Private method to handle loop nodes.

        @param node reference to the loop node to handle
        @type ast.For, ast.AsyncFor or ast.While
        """
        self.__loopCount += 1
        self.generic_visit(node)
        self.__loopCount -= 1

    def __visitWithStack(self, node):
        """
        Private method to traverse a given function node using a stack.

        @param node AST node to be traversed
        @type ast.FunctionDef or ast.AsyncFunctionDef
        """
        self.__stack.append(
            {
                ReturnVisitor.Assigns: defaultdict(list),
                ReturnVisitor.Refs: defaultdict(list),
                ReturnVisitor.Returns: [],
            }
        )

        self.generic_visit(node)
        self.__checkFunction(node)
        self.__stack.pop()

    def visit_FunctionDef(self, node):
        """
        Public method to handle a function definition.

        @param node reference to the node to handle
        @type ast.FunctionDef
        """
        self.__visitWithStack(node)

    def visit_AsyncFunctionDef(self, node):
        """
        Public method to handle a function definition.

        @param node reference to the node to handle
        @type ast.AsyncFunctionDef
        """
        self.__visitWithStack(node)

    def visit_Return(self, node):
        """
        Public method to handle a return node.

        @param node reference to the node to handle
        @type ast.Return
        """
        self.returns.append(node)
        self.generic_visit(node)

    def visit_Assign(self, node):
        """
        Public method to handle an assign node.

        @param node reference to the node to handle
        @type ast.Assign
        """
        if not self.__stack:
            return

        self.generic_visit(node.value)

        target = node.targets[0]
        if isinstance(target, ast.Tuple) and not isinstance(node.value, ast.Tuple):
            # skip unpacking assign
            return

        self.__visitAssignTarget(target)

    def visit_Name(self, node):
        """
        Public method to handle a name node.

        @param node reference to the node to handle
        @type ast.Name
        """
        if self.__stack:
            self.refs[node.id].append(node.lineno)

    def __visitAssignTarget(self, node):
        """
        Private method to handle an assign target node.

        @param node reference to the node to handle
        @type ast.AST
        """
        if isinstance(node, ast.Tuple):
            for elt in node.elts:
                self.__visitAssignTarget(elt)
            return

        if not self.__loopCount and isinstance(node, ast.Name):
            self.assigns[node.id].append(node.lineno)
            return

        self.generic_visit(node)

    def __checkFunction(self, node):
        """
        Private method to check a function definition node.

        @param node reference to the node to check
        @type ast.AsyncFunctionDef or ast.FunctionDef
        """
        if not self.returns or not node.body:
            return

        if len(node.body) == 1 and isinstance(node.body[-1], ast.Return):
            # skip functions that consist of `return None` only
            return

        if not self.__resultExists():
            self.__checkUnnecessaryReturnNone()
            return

        self.__checkImplicitReturnValue()
        self.__checkImplicitReturn(node.body[-1])

        for n in self.returns:
            if n.value:
                self.__checkUnnecessaryAssign(n.value)

    def __isNone(self, node):
        """
        Private method to check, if a node value is None.

        @param node reference to the node to check
        @type ast.AST
        @return flag indicating the node contains a None value
        @rtype bool
        """
        return AstUtilities.isNameConstant(node) and AstUtilities.getValue(node) is None

    def __isFalse(self, node):
        """
        Private method to check, if a node value is False.

        @param node reference to the node to check
        @type ast.AST
        @return flag indicating the node contains a False value
        @rtype bool
        """
        return (
            AstUtilities.isNameConstant(node) and AstUtilities.getValue(node) is False
        )

    def __resultExists(self):
        """
        Private method to check the existance of a return result.

        @return flag indicating the existence of a return result
        @rtype bool
        """
        for node in self.returns:
            value = node.value
            if value and not self.__isNone(value):
                return True

        return False

    def __checkImplicitReturnValue(self):
        """
        Private method to check for implicit return values.
        """
        for node in self.returns:
            if not node.value:
                self.violations.append((node, "M832"))

    def __checkUnnecessaryReturnNone(self):
        """
        Private method to check for an unnecessary 'return None' statement.
        """
        for node in self.returns:
            if self.__isNone(node.value):
                self.violations.append((node, "M831"))

    def __checkImplicitReturn(self, node):
        """
        Private method to check for an implicit return statement.

        @param node reference to the node to check
        @type ast.AST
        """
        if isinstance(node, ast.If):
            if not node.body or not node.orelse:
                self.violations.append((node, "M833"))
                return

            self.__checkImplicitReturn(node.body[-1])
            self.__checkImplicitReturn(node.orelse[-1])
            return

        if isinstance(node, (ast.For, ast.AsyncFor)) and node.orelse:
            self.__checkImplicitReturn(node.orelse[-1])
            return

        if isinstance(node, (ast.With, ast.AsyncWith)):
            self.__checkImplicitReturn(node.body[-1])
            return

        if isinstance(node, ast.Assert) and self.__isFalse(node.test):
            return

        try:
            okNodes = (ast.Return, ast.Raise, ast.While, ast.Try)
        except AttributeError:
            okNodes = (ast.Return, ast.Raise, ast.While)
        if not isinstance(node, okNodes):
            self.violations.append((node, "M833"))

    def __checkUnnecessaryAssign(self, node):
        """
        Private method to check for an unnecessary assign statement.

        @param node reference to the node to check
        @type ast.AST
        """
        if not isinstance(node, ast.Name):
            return

        varname = node.id
        returnLineno = node.lineno

        if varname not in self.assigns:
            return

        if varname not in self.refs:
            self.violations.append((node, "M834"))
            return

        if self.__hasRefsBeforeNextAssign(varname, returnLineno):
            return

        self.violations.append((node, "M834"))

    def __hasRefsBeforeNextAssign(self, varname, returnLineno):
        """
        Private method to check for references before a following assign
        statement.

        @param varname variable name to check for
        @type str
        @param returnLineno line number of the return statement
        @type int
        @return flag indicating the existence of references
        @rtype bool
        """
        beforeAssign = 0
        afterAssign = None

        for lineno in sorted(self.assigns[varname]):
            if lineno > returnLineno:
                afterAssign = lineno
                break

            if lineno <= returnLineno:
                beforeAssign = lineno

        for lineno in self.refs[varname]:
            if lineno == returnLineno:
                continue

            if afterAssign:
                if beforeAssign < lineno <= afterAssign:
                    return True

            elif beforeAssign < lineno:
                return True

        return False


class DateTimeVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check datetime function calls.

    Note: This class is modeled after flake8_datetimez checker.
    """

    def __init__(self):
        """
        Constructor
        """
        super().__init__()

        self.violations = []

    def __getFromKeywords(self, keywords, name):
        """
        Private method to get a keyword node given its name.

        @param keywords list of keyword argument nodes
        @type list of ast.AST
        @param name name of the keyword node
        @type str
        @return keyword node
        @rtype ast.AST
        """
        for keyword in keywords:
            if keyword.arg == name:
                return keyword

        return None

    def visit_Call(self, node):
        """
        Public method to handle a function call.

        Every datetime related function call is check for use of the naive
        variant (i.e. use without TZ info).

        @param node reference to the node to be processed
        @type ast.Call
        """
        # datetime.something()
        isDateTimeClass = (
            isinstance(node.func, ast.Attribute)
            and isinstance(node.func.value, ast.Name)
            and node.func.value.id == "datetime"
        )

        # datetime.datetime.something()
        isDateTimeModuleAndClass = (
            isinstance(node.func, ast.Attribute)
            and isinstance(node.func.value, ast.Attribute)
            and node.func.value.attr == "datetime"
            and isinstance(node.func.value.value, ast.Name)
            and node.func.value.value.id == "datetime"
        )

        if isDateTimeClass:
            if node.func.attr == "datetime":
                # datetime.datetime(2000, 1, 1, 0, 0, 0, 0,
                #                   datetime.timezone.utc)
                isCase1 = len(node.args) >= 8 and not (
                    AstUtilities.isNameConstant(node.args[7])
                    and AstUtilities.getValue(node.args[7]) is None
                )

                # datetime.datetime(2000, 1, 1, tzinfo=datetime.timezone.utc)
                tzinfoKeyword = self.__getFromKeywords(node.keywords, "tzinfo")
                isCase2 = tzinfoKeyword is not None and not (
                    AstUtilities.isNameConstant(tzinfoKeyword.value)
                    and AstUtilities.getValue(tzinfoKeyword.value) is None
                )

                if not (isCase1 or isCase2):
                    self.violations.append((node, "M301"))

            elif node.func.attr == "time":
                # time(12, 10, 45, 0, datetime.timezone.utc)
                isCase1 = len(node.args) >= 5 and not (
                    AstUtilities.isNameConstant(node.args[4])
                    and AstUtilities.getValue(node.args[4]) is None
                )

                # datetime.time(12, 10, 45, tzinfo=datetime.timezone.utc)
                tzinfoKeyword = self.__getFromKeywords(node.keywords, "tzinfo")
                isCase2 = tzinfoKeyword is not None and not (
                    AstUtilities.isNameConstant(tzinfoKeyword.value)
                    and AstUtilities.getValue(tzinfoKeyword.value) is None
                )

                if not (isCase1 or isCase2):
                    self.violations.append((node, "M321"))

            elif node.func.attr == "date":
                self.violations.append((node, "M311"))

        if isDateTimeClass or isDateTimeModuleAndClass:
            if node.func.attr == "today":
                self.violations.append((node, "M302"))

            elif node.func.attr == "utcnow":
                self.violations.append((node, "M303"))

            elif node.func.attr == "utcfromtimestamp":
                self.violations.append((node, "M304"))

            elif node.func.attr in "now":
                # datetime.now(UTC)
                isCase1 = (
                    len(node.args) == 1
                    and len(node.keywords) == 0
                    and not (
                        AstUtilities.isNameConstant(node.args[0])
                        and AstUtilities.getValue(node.args[0]) is None
                    )
                )

                # datetime.now(tz=UTC)
                tzKeyword = self.__getFromKeywords(node.keywords, "tz")
                isCase2 = tzKeyword is not None and not (
                    AstUtilities.isNameConstant(tzKeyword.value)
                    and AstUtilities.getValue(tzKeyword.value) is None
                )

                if not (isCase1 or isCase2):
                    self.violations.append((node, "M305"))

            elif node.func.attr == "fromtimestamp":
                # datetime.fromtimestamp(1234, UTC)
                isCase1 = (
                    len(node.args) == 2
                    and len(node.keywords) == 0
                    and not (
                        AstUtilities.isNameConstant(node.args[1])
                        and AstUtilities.getValue(node.args[1]) is None
                    )
                )

                # datetime.fromtimestamp(1234, tz=UTC)
                tzKeyword = self.__getFromKeywords(node.keywords, "tz")
                isCase2 = tzKeyword is not None and not (
                    AstUtilities.isNameConstant(tzKeyword.value)
                    and AstUtilities.getValue(tzKeyword.value) is None
                )

                if not (isCase1 or isCase2):
                    self.violations.append((node, "M306"))

            elif node.func.attr == "strptime":
                # datetime.strptime(...).replace(tzinfo=UTC)
                parent = getattr(node, "_dtCheckerParent", None)
                pparent = getattr(parent, "_dtCheckerParent", None)
                if not (
                    isinstance(parent, ast.Attribute) and parent.attr == "replace"
                ) or not isinstance(pparent, ast.Call):
                    isCase1 = False
                else:
                    tzinfoKeyword = self.__getFromKeywords(pparent.keywords, "tzinfo")
                    isCase1 = tzinfoKeyword is not None and not (
                        AstUtilities.isNameConstant(tzinfoKeyword.value)
                        and AstUtilities.getValue(tzinfoKeyword.value) is None
                    )

                if not isCase1:
                    self.violations.append((node, "M307"))

            elif node.func.attr == "fromordinal":
                self.violations.append((node, "M308"))

        # date.something()
        isDateClass = (
            isinstance(node.func, ast.Attribute)
            and isinstance(node.func.value, ast.Name)
            and node.func.value.id == "date"
        )

        # datetime.date.something()
        isDateModuleAndClass = (
            isinstance(node.func, ast.Attribute)
            and isinstance(node.func.value, ast.Attribute)
            and node.func.value.attr == "date"
            and isinstance(node.func.value.value, ast.Name)
            and node.func.value.value.id == "datetime"
        )

        if isDateClass or isDateModuleAndClass:
            if node.func.attr == "today":
                self.violations.append((node, "M312"))

            elif node.func.attr == "fromtimestamp":
                self.violations.append((node, "M313"))

            elif node.func.attr == "fromordinal":
                self.violations.append((node, "M314"))

            elif node.func.attr == "fromisoformat":
                self.violations.append((node, "M315"))

        self.generic_visit(node)


class SysVersionVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check the use of sys.version and
    sys.version_info.

    Note: This class is modeled after flake8-2020 checker.
    """

    def __init__(self):
        """
        Constructor
        """
        super().__init__()

        self.violations = []
        self.__fromImports = {}

    def visit_ImportFrom(self, node):
        """
        Public method to handle a from ... import ... statement.

        @param node reference to the node to be processed
        @type ast.ImportFrom
        """
        for alias in node.names:
            if node.module is not None and not alias.asname:
                self.__fromImports[alias.name] = node.module

        self.generic_visit(node)

    def __isSys(self, attr, node):
        """
        Private method to check for a reference to sys attribute.

        @param attr attribute name
        @type str
        @param node reference to the node to be checked
        @type ast.Node
        @return flag indicating a match
        @rtype bool
        """
        match = False
        if (
            isinstance(node, ast.Attribute)
            and isinstance(node.value, ast.Name)
            and node.value.id == "sys"
            and node.attr == attr
        ) or (
            isinstance(node, ast.Name)
            and node.id == attr
            and self.__fromImports.get(node.id) == "sys"
        ):
            match = True

        return match

    def __isSysVersionUpperSlice(self, node, n):
        """
        Private method to check the upper slice of sys.version.

        @param node reference to the node to be checked
        @type ast.Node
        @param n slice value to check against
        @type int
        @return flag indicating a match
        @rtype bool
        """
        return (
            self.__isSys("version", node.value)
            and isinstance(node.slice, ast.Slice)
            and node.slice.lower is None
            and AstUtilities.isNumber(node.slice.upper)
            and AstUtilities.getValue(node.slice.upper) == n
            and node.slice.step is None
        )

    def visit_Subscript(self, node):
        """
        Public method to handle a subscript.

        @param node reference to the node to be processed
        @type ast.Subscript
        """
        if self.__isSysVersionUpperSlice(node, 1):
            self.violations.append((node.value, "M423"))
        elif self.__isSysVersionUpperSlice(node, 3):
            self.violations.append((node.value, "M401"))
        elif (
            self.__isSys("version", node.value)
            and isinstance(node.slice, ast.Index)
            and AstUtilities.isNumber(node.slice.value)
            and AstUtilities.getValue(node.slice.value) == 2
        ):
            self.violations.append((node.value, "M402"))
        elif (
            self.__isSys("version", node.value)
            and isinstance(node.slice, ast.Index)
            and AstUtilities.isNumber(node.slice.value)
            and AstUtilities.getValue(node.slice.value) == 0
        ):
            self.violations.append((node.value, "M421"))

        self.generic_visit(node)

    def visit_Compare(self, node):
        """
        Public method to handle a comparison.

        @param node reference to the node to be processed
        @type ast.Compare
        """
        if (
            isinstance(node.left, ast.Subscript)
            and self.__isSys("version_info", node.left.value)
            and isinstance(node.left.slice, ast.Index)
            and AstUtilities.isNumber(node.left.slice.value)
            and AstUtilities.getValue(node.left.slice.value) == 0
            and len(node.ops) == 1
            and isinstance(node.ops[0], ast.Eq)
            and AstUtilities.isNumber(node.comparators[0])
            and AstUtilities.getValue(node.comparators[0]) == 3
        ):
            self.violations.append((node.left, "M411"))
        elif (
            self.__isSys("version", node.left)
            and len(node.ops) == 1
            and isinstance(node.ops[0], (ast.Lt, ast.LtE, ast.Gt, ast.GtE))
            and AstUtilities.isString(node.comparators[0])
        ):
            if len(AstUtilities.getValue(node.comparators[0])) == 1:
                errorCode = "M422"
            else:
                errorCode = "M403"
            self.violations.append((node.left, errorCode))
        elif (
            isinstance(node.left, ast.Subscript)
            and self.__isSys("version_info", node.left.value)
            and isinstance(node.left.slice, ast.Index)
            and AstUtilities.isNumber(node.left.slice.value)
            and AstUtilities.getValue(node.left.slice.value) == 1
            and len(node.ops) == 1
            and isinstance(node.ops[0], (ast.Lt, ast.LtE, ast.Gt, ast.GtE))
            and AstUtilities.isNumber(node.comparators[0])
        ):
            self.violations.append((node, "M413"))
        elif (
            isinstance(node.left, ast.Attribute)
            and self.__isSys("version_info", node.left.value)
            and node.left.attr == "minor"
            and len(node.ops) == 1
            and isinstance(node.ops[0], (ast.Lt, ast.LtE, ast.Gt, ast.GtE))
            and AstUtilities.isNumber(node.comparators[0])
        ):
            self.violations.append((node, "M414"))

        self.generic_visit(node)

    def visit_Attribute(self, node):
        """
        Public method to handle an attribute.

        @param node reference to the node to be processed
        @type ast.Attribute
        """
        if (
            isinstance(node.value, ast.Name)
            and node.value.id == "six"
            and node.attr == "PY3"
        ):
            self.violations.append((node, "M412"))

        self.generic_visit(node)

    def visit_Name(self, node):
        """
        Public method to handle an name.

        @param node reference to the node to be processed
        @type ast.Name
        """
        if node.id == "PY3" and self.__fromImports.get(node.id) == "six":
            self.violations.append((node, "M412"))

        self.generic_visit(node)


#
# eflag: noqa = M891