# 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

__all__ = ['WeakSet']


class _IterationGuard(object):
# 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(object):
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):
l = self._pending_removals
discard = self.data.discard
while l:
discard(l.pop())

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),),
getattr(self, '__dict__', None))

__hash__ = None

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')
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(ref(item) for item in 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(ref(item) for item in other)

def __eq__(self, other):
if not isinstance(other, self.__class__):
return NotImplemented
return self.data == set(ref(item) for item in other)

def __ne__(self, other):
opposite = self.__eq__(other)
if opposite is NotImplemented:
return NotImplemented
return not opposite

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