--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/E5Utilities/E5Cache.py Tue Oct 03 19:37:44 2017 +0200
@@ -0,0 +1,172 @@
+# -*- coding: utf-8 -*-
+
+# Copyright (c) 2017 Detlev Offenbach <detlev@die-offenbachs.de>
+#
+
+"""
+Module implementing classes used for caching objects.
+"""
+
+from __future__ import unicode_literals
+
+
+class E5Cache(object):
+ """
+ Class implementing a LRU cache of a specific size.
+
+ If the maximum number of entries is exceeded, the least recently used item
+ is removed from the cache. A cache hit moves the entry to the front of the
+ cache.
+ """
+ def __init__(self, size=100):
+ """
+ Constructor
+
+ @param size maximum number of entries that may be stored in the cache
+ @type int
+ """
+ assert size >= 0
+
+ self.__size = size
+
+ # internal objects
+ self.__keyList = []
+ self.__store = {}
+ self.__hits = 0
+ self.__misses = 0
+ self.__maxsize = 0
+
+ def __moveLast(self, key):
+ """
+ Private method to move a cached item to the MRU position.
+
+ @param key key of the item to be retrieved
+ @type any hashable type that can be used as a dict key
+ """
+ self.__keyList.remove(key)
+ self.__keyList.append(key)
+
+ def __adjustToSize(self):
+ """
+ Private method to adjust the cache to its size.
+ """
+ while len(self.__keyList) > self.__size:
+ key = self.__keyList.pop(0)
+ del self.__store[key]
+
+ def getSize(self):
+ """
+ Public method to get the size of the cache.
+
+ @return maximum number of entries of the cache
+ @rtype int
+ """
+ return self.__size
+
+ def setSize(self, newSize):
+ """
+ Public method to change the size of the cache.
+
+ @param newSize maximum number of entries that may be stored in the
+ cache
+ @type int
+ """
+ assert newSize >= 0
+
+ self.__size = newSize
+ self.__adjustToSize()
+
+ def get(self, key):
+ """
+ Public method to get an entry from the cache given its key.
+
+ If the key is present in the cache, it is moved to the MRU position.
+
+ @param key key of the item to be retrieved
+ @type any hashable type that can be used as a dict key
+ @return cached item for the given key or None, if the key is not
+ present
+ @rtype object or None
+ """
+ if key in self.__store:
+ self.__hits += 1
+ self.__moveLast(key)
+ return self.__store[key]
+ else:
+ self.__misses += 1
+ return None
+
+ def add(self, key, item):
+ """
+ Public method to add an item to the cache.
+
+ If the key is already in use, the cached item is replaced by the new
+ one given and is moved to the MRU position
+
+ @param key key of the item to be retrieved
+ @type any hashable type that can be used as a dict key
+ @param item item to be cached under the given key
+ @type object
+ """
+ if key in self.__store:
+ self.__moveLast(key)
+ else:
+ self.__keyList.append(key)
+ self.__store[key] = item
+
+ self.__adjustToSize()
+
+ self.__maxsize = max(self.__maxsize, len(self.__keyList))
+
+ def remove(self, key):
+ """
+ Public method to remove an item from the cache.
+
+ @param key key of the item to be retrieved
+ @type any hashable type that can be used as a dict key
+ """
+ if key in self.__store:
+ del self.__store[key]
+ self.__keyList.remove(key)
+
+ def clear(self):
+ """
+ Public method to clear the cache.
+ """
+ self.__keyList = []
+ self.__store = {}
+
+ def reset(self):
+ """
+ Public method to reset the cache.
+
+ This is like clear() but sets the various counters to their initial
+ value as well.
+ """
+ self.clear()
+ self.__hits = 0
+ self.__misses = 0
+ self.__maxsize = 0
+
+ def length(self):
+ """
+ Public method to get the current length of the cache.
+
+ @return current length of the cache
+ @rtype int
+ """
+ return len(self.__keyList)
+
+ def info(self):
+ """
+ Public method to get some information about the cache.
+
+ @return dictionary containing the cache info
+ @rtype dict (with keys "hits", "misses", "maxsize", "currsize")
+ """
+ return {
+ "hits": self.__hits,
+ "misses": self.__misses,
+ "maxsize": self.__maxsize,
+ "currsize": self.length(),
+ }
