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from collections.abc import MutableMapping
class _DefaultSize:
__slots__ = ()
def __getitem__(self, _):
return 1
def __setitem__(self, _, value):
assert value == 1
def pop(self, _):
return 1
class Cache(MutableMapping):
"""Mutable mapping to serve as a simple cache or cache base class."""
__marker = object()
__size = _DefaultSize()
def __init__(self, maxsize, getsizeof=None):
if getsizeof:
self.getsizeof = getsizeof
if self.getsizeof is not Cache.getsizeof:
self.__size = dict()
self.__data = dict()
self.__currsize = 0
self.__maxsize = maxsize
def __repr__(self):
return "%s(%r, maxsize=%r, currsize=%r)" % (
self.__class__.__name__,
list(self.__data.items()),
self.__maxsize,
self.__currsize,
)
def __getitem__(self, key):
try:
return self.__data[key]
except KeyError:
return self.__missing__(key)
def __setitem__(self, key, value):
maxsize = self.__maxsize
size = self.getsizeof(value)
if size > maxsize:
raise ValueError("value too large")
if key not in self.__data or self.__size[key] < size:
while self.__currsize + size > maxsize:
self.popitem()
if key in self.__data:
diffsize = size - self.__size[key]
else:
diffsize = size
self.__data[key] = value
self.__size[key] = size
self.__currsize += diffsize
def __delitem__(self, key):
size = self.__size.pop(key)
del self.__data[key]
self.__currsize -= size
def __contains__(self, key):
return key in self.__data
def __missing__(self, key):
raise KeyError(key)
def __iter__(self):
return iter(self.__data)
def __len__(self):
return len(self.__data)
def get(self, key, default=None):
if key in self:
return self[key]
else:
return default
def pop(self, key, default=__marker):
if key in self:
value = self[key]
del self[key]
elif default is self.__marker:
raise KeyError(key)
else:
value = default
return value
def setdefault(self, key, default=None):
if key in self:
value = self[key]
else:
self[key] = value = default
return value
@property
def maxsize(self):
"""The maximum size of the cache."""
return self.__maxsize
@property
def currsize(self):
"""The current size of the cache."""
return self.__currsize
@staticmethod
def getsizeof(value):
"""Return the size of a cache element's value."""
return 1
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