eric6/Plugins/CheckerPlugins/CodeStyleChecker/Miscellaneous/MiscellaneousChecker.py

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

# Copyright (c) 2015 - 2020 Detlev Offenbach <detlev@die-offenbachs.de>
#

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

import sys
import ast
import re
import itertools
from string import Formatter
from collections import defaultdict
import tokenize

import AstUtilities


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
    @return call path components
    @rtype str
    """
    if isinstance(node, ast.Attribute):
        for v in composeCallPath(node.value):
            yield v
        yield node.attr
    elif isinstance(node, ast.Name):
        yield node.id


class MiscellaneousChecker(object):
    """
    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",
        "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", "M506", "M507", "M508",
        "M509",
        "M511", "M512", "M513",
        "M521", "M522", "M523", "M524",
        
        ## 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",
        
        ## syntax error
        "M901",
    ]
    
    Formatter = Formatter()
    FormatFieldRegex = re.compile(r'^((?:\s|.)*?)(\..*|\[.*\])?$')
    
    BuiltinsWhiteList = [
        "__name__",
        "__doc__",
        "credits",
    ]

    def __init__(self, source, filename, 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 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.__args = args
        
        self.__pep3101FormatRegex = re.compile(
            r'^(?:[^\'"]*[\'"][^\'"]*[\'"])*\s*%|^\s*%')
        
        import builtins
        self.__builtins = [b for b in dir(builtins)
                           if b not in self.BuiltinsWhiteList]

        # 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",
                                          "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",
                                   "M506", "M507", "M508", "M509",
                                   "M511", "M512", "M513",
                                   "M521", "M522", "M523", "M524")),
            (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",)),
        ]
        
        self.__defaultArgs = {
            "BuiltinsChecker": {
                "chr": ["unichr", ],
                "str": ["unicode", ],
            },
            "CodingChecker": 'latin-1, utf-8',
            "CopyrightChecker": {
                "Author": "",
                "MinFilesize": 0,
            },
            "CommentedCodeChecker": {
                "Aggressive": 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 __reportInvalidSyntax(self):
        """
        Private method to report a syntax error.
        """
        exc_type, exc = sys.exc_info()[:2]
        if len(exc.args) > 1:
            offset = exc.args[1]
            if len(offset) > 2:
                offset = offset[1:3]
        else:
            offset = (1, 0)
        self.__error(offset[0] - 1, offset[1] or 0,
                     'M901', exc_type.__name__, exc.args[0])
    
    def __generateTree(self):
        """
        Private method to generate an AST for our source.
        
        @return generated AST
        @rtype ast.AST
        """
        source = "".join(self.__source)
        return compile(source, self.__filename, 'exec', ast.PyCF_ONLY_AST)
    
    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
        
        try:
            self.__tree = self.__generateTree()
        except (SyntaxError, TypeError):
            self.__reportInvalidSyntax()
            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", self.__defaultArgs["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", self.__defaultArgs["CopyrightChecker"])
        copyrightMinFileSize = copyrightArgs.get(
            "MinFilesize",
            self.__defaultArgs["CopyrightChecker"]["MinFilesize"])
        copyrightAuthor = copyrightArgs.get(
            "Author",
            self.__defaultArgs["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.
        """
        from eradicate import commented_out_code_line_numbers
        
        source = "".join(self.__source)
        commentedCodeCheckerArgs = self.__args.get(
            "CommentedCodeChecker", self.__defaultArgs["CommentedCodeChecker"])
        aggressive = commentedCodeCheckerArgs.get(
            "Aggressive",
            self.__defaultArgs["CommentedCodeChecker"]["Aggressive"])
        for markedLine in 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 not (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
                if sys.version_info < (3, 5):
                    hasKwArgs = bool(call.kwargs)
                    hasStarArgs = bool(call.starargs)
                else:
                    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:
                    if not names:
                        # No names but kwargs
                        self.__error(call.lineno - 1, call.col_offset, "M623")
                if hasStarArgs:
                    if 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]
        try:
            functionDefs.append(ast.AsyncFunctionDef)
        except AttributeError:
            pass
        
        ignoreBuiltinAssignments = self.__args.get(
            "BuiltinsChecker", self.__defaultArgs["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)
                
                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) and
                    isinstance(node.args[0].elt, ast.Tuple) and
                    len(node.args[0].elt.elts) == 2 and
                    node.func.id == "dict"
                ):
                    self.__error(node.lineno - 1, node.col_offset, "M183")
                
                elif (
                    nArgs == 1 and
                    isinstance(node.args[0], ast.ListComp) and
                    node.func.id in ('list', 'set', 'dict')
                ):
                    errorCode = {
                        'list': 'M195',
                        'dict': 'M185',
                        '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 == 1 and
                    isinstance(node.args[0], ast.ListComp) and
                    node.func.id in ('all', 'any', 'enumerate', 'frozenset',
                                     'max', 'min', 'sorted', 'sum', 'tuple',)
                ):
                    self.__error(node.lineno - 1, node.col_offset, "M187",
                                 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 in ("tuple", "list", "dict")
                ):
                    self.__error(node.lineno - 1, node.col_offset, "M186",
                                 node.func.id)
                
                elif isinstance(node, ast.Compare) and (
                    len(node.ops) == 1 and
                    isinstance(node.ops[0], ast.In) and
                    len(node.comparators) == 1 and
                    isinstance(node.comparators[0], ast.ListComp)
                ):
                    self.__error(node.lineno - 1, node.col_offset, "M196")
    
    def __checkMutableDefault(self):
        """
        Private method to check for use of mutable types as default arguments.
        """
        mutableTypes = (
            ast.Call,
            ast.Dict,
            ast.List,
            ast.Set,
        )
        mutableCalls = (
            "Counter",
            "OrderedDict",
            "collections.Counter",
            "collections.OrderedDict",
            "collections.defaultdict",
            "collections.deque",
            "defaultdict",
            "deque",
            "dict",
            "list",
            "set",
        )
        immutableCalls = (
            "tuple",
            "frozenset",
        )
        functionDefs = [ast.FunctionDef]
        try:
            functionDefs.append(ast.AsyncFunctionDef)
        except AttributeError:
            pass
        
        for node in ast.walk(self.__tree):
            if any(isinstance(node, functionDef)
                   for functionDef in functionDefs):
                defaults = node.args.defaults[:]
                try:
                    defaults += node.args.kw_defaults[:]
                except AttributeError:
                    pass
                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 = self.__generateTree()
        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.
    """
    # modelled after the string format flake8 extension
    
    def __init__(self):
        """
        Constructor
        """
        super(TextVisitor, self).__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(TextVisitor, self).generic_visit(node)
        else:
            super(TextVisitor, self).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(TextVisitor, self).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(LoggingVisitor, self).__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
        """
        try:
            if node.func.value.id == "warnings":
                return None
            
            if node.func.attr in LoggingVisitor.LoggingLevels:
                return node.func.attr
        except AttributeError:
            pass
        
        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():
            if self.__withinLoggingArgument() and self.__isFormatCall(node):
                self.violations.append((node, "M651"))
                super(LoggingVisitor, self).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(LoggingVisitor, self).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(LoggingVisitor, self).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(LoggingVisitor, 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
        """
        if sys.version_info >= (3, 6):
            if self.__withinLoggingStatement():
                if any(isinstance(i, ast.FormattedValue) for i in node.values):
                    if self.__withinLoggingArgument():
                        self.violations.append((node, "M654"))
                        
                        super(LoggingVisitor, self).generic_visit(node)


class BugBearVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check for various topics.
    """
    #
    # This class was implemented along the BugBear flake8 extension (v 19.3.0).
    # Original: Copyright (c) 2016 Łukasz Langa
    #
    
    NodeWindowSize = 4
    
    def __init__(self):
        """
        Constructor
        """
        super(BugBearVisitor, self).__init__()
        
        self.__nodeStack = []
        self.__nodeWindow = []
        self.violations = []
    
    def visit(self, node):
        """
        Public method to traverse a given AST node.
        
        @param node AST node to be traversed
        @type ast.Node
        """
        self.__nodeStack.append(node)
        self.__nodeWindow.append(node)
        self.__nodeWindow = self.__nodeWindow[-BugBearVisitor.NodeWindowSize:]
        
        super(BugBearVisitor, self).visit(node)
        
        self.__nodeStack.pop()
    
    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, "M501"))
        
        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
        """
        validPaths = ("six", "future.utils", "builtins")
        methodsDict = {
            "M521": ("iterkeys", "itervalues", "iteritems", "iterlists"),
            "M522": ("viewkeys", "viewvalues", "viewitems", "viewlists"),
            "M523": ("next",),
        }
        
        if isinstance(node.func, ast.Attribute):
            for code, methods in methodsDict.items():
                if node.func.attr in methods:
                    callPath = ".".join(composeCallPath(node.func.value))
                    if callPath not in validPaths:
                        self.violations.append((node, code))
                    break
            else:
                self.__checkForM502(node)
        else:
            try:
                # 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, "M509"))
                
                # bad getattr and setattr
                if (
                    node.func.id in ("getattr", "hasattr") and
                    node.args[1].s == "__call__"
                ):
                    self.violations.append((node, "M511"))
                if (
                    node.func.id == "getattr" and
                    len(node.args) == 2 and
                    AstUtilities.isString(node.args[1])
                ):
                    self.violations.append((node, "M512"))
                elif (
                    node.func.id == "setattr" and
                    len(node.args) == 3 and
                    AstUtilities.isString(node.args[1])
                ):
                    self.violations.append((node, "M513"))
            except (AttributeError, IndexError):
                pass

            self.generic_visit(node)
    
    def visit_Attribute(self, node):
        """
        Public method to handle attributes.
        
        @param node reference to the node to be processed
        @type ast.Attribute
        """
        callPath = list(composeCallPath(node))
        
        if '.'.join(callPath) == 'sys.maxint':
            self.violations.append((node, "M504"))
        
        elif (
            len(callPath) == 2 and
            callPath[1] == 'message'
        ):
            name = callPath[0]
            for elem in reversed(self.__nodeStack[:-1]):
                if isinstance(elem, ast.ExceptHandler) and elem.name == name:
                    self.violations.append((node, "M505"))
                    break
    
    def visit_Assign(self, node):
        """
        Public method to handle assignments.
        
        @param node reference to the node to be processed
        @type ast.Assign
        """
        if isinstance(self.__nodeStack[-2], ast.ClassDef):
            # By using 'hasattr' below we're ignoring starred arguments, slices
            # and tuples for simplicity.
            assignTargets = {t.id for t in node.targets if hasattr(t, 'id')}
            if '__metaclass__' in assignTargets:
                self.violations.append((node, "M524"))
        
        elif len(node.targets) == 1:
            target = node.targets[0]
            if (
                isinstance(target, ast.Attribute) and
                isinstance(target.value, ast.Name)
            ):
                if (target.value.id, target.attr) == ('os', 'environ'):
                    self.violations.append((node, "M506"))
        
        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.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.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, "M503"))
        
        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
        """
        if sys.version_info >= (3, 6):
            for value in node.values:
                if isinstance(value, ast.FormattedValue):
                    return
            
            self.violations.append((node, "M508"))
    
    def __checkForM502(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, "M502"))
    
    def __checkForM507(self, node):
        """
        Private method to check for unused loop variables.
        
        @param node reference to the node to be processed
        @type ast.For
        """
        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))


class NameFinder(ast.NodeVisitor):
    """
    Class to extract a name out of a tree of nodes.
    """
    def __init__(self):
        """
        Constructor
        """
        super(NameFinder, self).__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
        """
        if isinstance(node, list):
            for elem in node:
                super(NameFinder, self).visit(elem)
        else:
            super(NameFinder, self).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 ReturnVisitor(ast.NodeVisitor):
    """
    Class implementing a node visitor to check return statements.
    """
    Assigns = 'assigns'
    Refs = 'refs'
    Returns = 'returns'
    
    def __init__(self):
        """
        Constructor
        """
        super(ReturnVisitor, self).__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 modelled after flake8_datetimez checker.
    """
    def __init__(self):
        """
        Constructor
        """
        super(DateTimeVisitor, self).__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'):
                    isCase1 = False
                elif 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 modelled after flake8-2020 checker.
    """
    def __init__(self):
        """
        Constructor
        """
        super(SysVersionVisitor, self).__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
        ):
            match = True
        elif (
            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