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from datetime import timedelta
import weakref
from collections import OrderedDict
class _TzSingleton(type):
def __init__(cls, *args, **kwargs):
cls.__instance = None
super(_TzSingleton, cls).__init__(*args, **kwargs)
def __call__(cls):
if cls.__instance is None:
cls.__instance = super(_TzSingleton, cls).__call__()
return cls.__instance
class _TzFactory(type):
def instance(cls, *args, **kwargs):
"""Alternate constructor that returns a fresh instance"""
return type.__call__(cls, *args, **kwargs)
class _TzOffsetFactory(_TzFactory):
def __init__(cls, *args, **kwargs):
cls.__instances = weakref.WeakValueDictionary()
cls.__strong_cache = OrderedDict()
cls.__strong_cache_size = 8
def __call__(cls, name, offset):
if isinstance(offset, timedelta):
key = (name, offset.total_seconds())
else:
key = (name, offset)
instance = cls.__instances.get(key, None)
if instance is None:
instance = cls.__instances.setdefault(key,
cls.instance(name, offset))
cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)
# Remove an item if the strong cache is overpopulated
# TODO: Maybe this should be under a lock?
if len(cls.__strong_cache) > cls.__strong_cache_size:
cls.__strong_cache.popitem(last=False)
return instance
class _TzStrFactory(_TzFactory):
def __init__(cls, *args, **kwargs):
cls.__instances = weakref.WeakValueDictionary()
cls.__strong_cache = OrderedDict()
cls.__strong_cache_size = 8
def __call__(cls, s, posix_offset=False):
key = (s, posix_offset)
instance = cls.__instances.get(key, None)
if instance is None:
instance = cls.__instances.setdefault(key,
cls.instance(s, posix_offset))
cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)
# Remove an item if the strong cache is overpopulated
# TODO: Maybe this should be under a lock?
if len(cls.__strong_cache) > cls.__strong_cache_size:
cls.__strong_cache.popitem(last=False)
return instance
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