2 # This code is separated-out because it is needed
15     # This technique should be relatively thread-safe (since sets are).
31             s.remove(self)
39         def _remove(item, selfref=ref(self)):  argument
43                     self._pending_removals.append(item)
45                     self.data.discard(item)
58                 item = pop()
61             discard(item)
66                 item = itemref()
67                 if item is not None:
69                     # `item` until it is resumed or closed.
70                     yield item
73         return len(self.data) - len(self._pending_removals)
75     def __contains__(self, item):  argument
77             wr = ref(item)
85     def add(self, item):  argument
88         self.data.add(ref(item, self._remove))
106             item = itemref()
107             if item is not None:
108                 return item
110     def remove(self, item):  argument
113         self.data.remove(ref(item))
115     def discard(self, item):  argument
118         self.data.discard(ref(item))
144             self.data.difference_update(ref(item) for item in other)
148         return self.__class__(item for item in other if item in self)
156         self.data.intersection_update(ref(item) for item in other)
160         return self.data.issubset(ref(item) for item in other)
167         return self.data.issuperset(ref(item) for item in other)
192             self.data.symmetric_difference_update(ref(item, self._remove) for item in other)