# Access WeakSet through the weakref module.

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# This code is separated-out because it is needed

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# by abc.py to load everything else at startup.

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from _weakref import ref

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__all__ = ['WeakSet']

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class _IterationGuard:

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# This context manager registers itself in the current iterators of the

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# weak container, such as to delay all removals until the context manager

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# exits.

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# This technique should be relatively thread-safe (since sets are).

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def __init__(self, weakcontainer):

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# Don't create cycles

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self.weakcontainer = ref(weakcontainer)

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def __enter__(self):

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w = self.weakcontainer()

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if w is not None:

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w._iterating.add(self)

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return self

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def __exit__(self, e, t, b):

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w = self.weakcontainer()

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if w is not None:

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s = w._iterating

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s.remove(self)

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if not s:

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w._commit_removals()

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class WeakSet:

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def __init__(self, data=None):

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self.data = set()

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def _remove(item, selfref=ref(self)):

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self = selfref()

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if self is not None:

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if self._iterating:

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self._pending_removals.append(item)

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else:

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self.data.discard(item)

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self._remove = _remove

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# A list of keys to be removed

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self._pending_removals = []

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self._iterating = set()

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if data is not None:

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self.update(data)

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def _commit_removals(self):

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l = self._pending_removals

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discard = self.data.discard

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while l:

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discard(l.pop())

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def __iter__(self):

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with _IterationGuard(self):

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for itemref in self.data:

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item = itemref()

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if item is not None:

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# Caveat: the iterator will keep a strong reference to

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# `item` until it is resumed or closed.

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yield item

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def __len__(self):

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return len(self.data) - len(self._pending_removals)

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def __contains__(self, item):

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try:

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wr = ref(item)

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except TypeError:

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return False

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return wr in self.data

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def __reduce__(self):

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return (self.__class__, (list(self),),

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getattr(self, '__dict__', None))

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def add(self, item):

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if self._pending_removals:

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self._commit_removals()

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self.data.add(ref(item, self._remove))

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def clear(self):

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if self._pending_removals:

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self._commit_removals()

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self.data.clear()

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def copy(self):

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return self.__class__(self)

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def pop(self):

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if self._pending_removals:

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self._commit_removals()

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while True:

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try:

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itemref = self.data.pop()

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except KeyError:

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raise KeyError('pop from empty WeakSet')

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item = itemref()

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if item is not None:

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return item

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def remove(self, item):

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if self._pending_removals:

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self._commit_removals()

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self.data.remove(ref(item))

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def discard(self, item):

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if self._pending_removals:

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self._commit_removals()

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self.data.discard(ref(item))

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def update(self, other):

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if self._pending_removals:

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self._commit_removals()

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for element in other:

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self.add(element)

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def __ior__(self, other):

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self.update(other)

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return self

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def difference(self, other):

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newset = self.copy()

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newset.difference_update(other)

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return newset

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__sub__ = difference

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def difference_update(self, other):

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self.__isub__(other)

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def __isub__(self, other):

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if self._pending_removals:

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self._commit_removals()

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if self is other:

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self.data.clear()

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else:

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self.data.difference_update(ref(item) for item in other)

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return self

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def intersection(self, other):

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return self.__class__(item for item in other if item in self)

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__and__ = intersection

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def intersection_update(self, other):

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self.__iand__(other)

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def __iand__(self, other):

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if self._pending_removals:

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self._commit_removals()

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self.data.intersection_update(ref(item) for item in other)

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return self

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def issubset(self, other):

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return self.data.issubset(ref(item) for item in other)

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__le__ = issubset

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def __lt__(self, other):

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return self.data < set(ref(item) for item in other)

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def issuperset(self, other):

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return self.data.issuperset(ref(item) for item in other)

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__ge__ = issuperset

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def __gt__(self, other):

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return self.data > set(ref(item) for item in other)

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def __eq__(self, other):

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if not isinstance(other, self.__class__):

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return NotImplemented

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return self.data == set(ref(item) for item in other)

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def symmetric_difference(self, other):

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newset = self.copy()

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newset.symmetric_difference_update(other)

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return newset

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__xor__ = symmetric_difference

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def symmetric_difference_update(self, other):

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self.__ixor__(other)

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def __ixor__(self, other):

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if self._pending_removals:

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self._commit_removals()

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if self is other:

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self.data.clear()

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else:

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self.data.symmetric_difference_update(ref(item, self._remove) for item in other)

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return self

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def union(self, other):

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return self.__class__(e for s in (self, other) for e in s)

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__or__ = union

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def isdisjoint(self, other):

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return len(self.intersection(other)) == 0

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