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import collections
from .cache import Cache
class FIFOCache(Cache):
"""First In First Out (FIFO) cache implementation."""
def __init__(self, maxsize, getsizeof=None):
Cache.__init__(self, maxsize, getsizeof)
self.__order = collections.OrderedDict()
def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
cache_setitem(self, key, value)
try:
self.__order.move_to_end(key)
except KeyError:
self.__order[key] = None
def __delitem__(self, key, cache_delitem=Cache.__delitem__):
cache_delitem(self, key)
del self.__order[key]
def popitem(self):
"""Remove and return the `(key, value)` pair first inserted."""
try:
key = next(iter(self.__order))
except StopIteration:
raise KeyError("%s is empty" % type(self).__name__) from None
else:
return (key, self.pop(key))
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