# 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:
 # 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):
 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))

 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)