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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
__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:
                    yield item
    def __len__(self):
        return sum(x() is not None for x in self.data)
    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()
        if isinstance(other, self.__class__):
            self.data.update(other.data)
        else:
            for element in other:
                self.add(element)
    def __ior__(self, other):
        self.update(other)
        return self
    # Helper functions for simple delegating methods.
    def _apply(self, other, method):
        if not isinstance(other, self.__class__):
            other = self.__class__(other)
        newdata = method(other.data)
        newset = self.__class__()
        newset.data = newdata
        return newset
    def difference(self, other):
        return self._apply(other, self.data.difference)
    __sub__ = difference
    def difference_update(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)
    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._apply(other, self.data.intersection)
    __and__ = intersection
    def intersection_update(self, other):
        if self._pending_removals:
            self._commit_removals()
        self.data.intersection_update(ref(item) for item in 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)
    __lt__ = issubset
    def __le__(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)
    __gt__ = issuperset
    def __ge__(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 symmetric_difference(self, other):
        return self._apply(other, self.data.symmetric_difference)
    __xor__ = symmetric_difference
    def symmetric_difference_update(self, other):
        if self._pending_removals:
            self._commit_removals()
        if self is other:
            self.data.clear()
        else:
            self.data.symmetric_difference_update(ref(item) for item in 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) for item in other)
        return self
    def union(self, other):
        return self._apply(other, self.data.union)
    __or__ = union
    def isdisjoint(self, other):
        return len(self.intersection(other)) == 0
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