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# Access WeakSet through the weakref module.

# This code is separated-out because it is needed

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

from _weakref import ref

from types import GenericAlias

__all__ = ['WeakSet']

class _IterationGuard:

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

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

# exits.

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

def __init__(self, weakcontainer):

# Don't create cycles

self.weakcontainer = ref(weakcontainer)

def __enter__(self):

w = self.weakcontainer()

if w is not None:

w._iterating.add(self)

return self

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

w = self.weakcontainer()

if w is not None:

s = w._iterating

s.remove(self)

if not s:

w._commit_removals()

class WeakSet:

def __init__(self, data=None):

self.data = set()

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

self = selfref()

if self is not None:

if self._iterating:

self._pending_removals.append(item)

else:

self.data.discard(item)

self._remove = _remove

# A list of keys to be removed

self._pending_removals = []

self._iterating = set()

if data is not None:

self.update(data)

def _commit_removals(self):

pop = self._pending_removals.pop

discard = self.data.discard

while True:

try:

item = pop()

except IndexError:

return

discard(item)

def __iter__(self):

with _IterationGuard(self):

for itemref in self.data:

item = itemref()

if item is not None:

# Caveat: the iterator will keep a strong reference to

# `item` until it is resumed or closed.

yield item

def __len__(self):

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

def __contains__(self, item):

try:

wr = ref(item)

except TypeError:

return False

return wr in self.data

def __reduce__(self):

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

def add(self, item):

if self._pending_removals:

self._commit_removals()

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

def clear(self):

if self._pending_removals:

self._commit_removals()

self.data.clear()

def copy(self):

return self.__class__(self)

def pop(self):

if self._pending_removals:

self._commit_removals()

while True:

try:

itemref = self.data.pop()

except KeyError:

raise KeyError('pop from empty WeakSet') from None

item = itemref()

if item is not None:

return item

def remove(self, item):

if self._pending_removals:

self._commit_removals()

self.data.remove(ref(item))

def discard(self, item):

if self._pending_removals:

self._commit_removals()

self.data.discard(ref(item))

def update(self, other):

if self._pending_removals:

self._commit_removals()

for element in other:

self.add(element)

def __ior__(self, other):

self.update(other)

return self

def difference(self, other):

newset = self.copy()

newset.difference_update(other)

return newset

__sub__ = difference

def difference_update(self, other):

self.__isub__(other)

def __isub__(self, other):

if self._pending_removals:

self._commit_removals()

if self is other:

self.data.clear()

else:

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

return self

def intersection(self, other):

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

__and__ = intersection

def intersection_update(self, other):

self.__iand__(other)

def __iand__(self, other):

if self._pending_removals:

self._commit_removals()

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

return self

def issubset(self, other):

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

__le__ = issubset

def __lt__(self, other):

return self.data < set(map(ref, other))

def issuperset(self, other):

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

__ge__ = issuperset

def __gt__(self, other):

return self.data > set(map(ref, other))

def __eq__(self, other):

if not isinstance(other, self.__class__):

return NotImplemented

return self.data == set(map(ref, other))

def symmetric_difference(self, other):

newset = self.copy()

newset.symmetric_difference_update(other)

return newset

__xor__ = symmetric_difference

def symmetric_difference_update(self, other):

self.__ixor__(other)

def __ixor__(self, other):

if self._pending_removals:

self._commit_removals()

if self is other:

self.data.clear()

else:

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

return self

def union(self, other):

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

__or__ = union

def isdisjoint(self, other):

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

def __repr__(self):

return repr(self.data)

__class_getitem__ = classmethod(GenericAlias)

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