1# Access WeakSet through the weakref module.
2# This code is separated-out because it is needed
3# by abc.py to load everything else at startup.
4
5from _weakref import ref
6from types import GenericAlias
7
8__all__ = ['WeakSet']
9
10
11class _IterationGuard:
12    # This context manager registers itself in the current iterators of the
13    # weak container, such as to delay all removals until the context manager
14    # exits.
15    # This technique should be relatively thread-safe (since sets are).
16
17    def __init__(self, weakcontainer):
18        # Don't create cycles
19        self.weakcontainer = ref(weakcontainer)
20
21    def __enter__(self):
22        w = self.weakcontainer()
23        if w is not None:
24            w._iterating.add(self)
25        return self
26
27    def __exit__(self, e, t, b):
28        w = self.weakcontainer()
29        if w is not None:
30            s = w._iterating
31            s.remove(self)
32            if not s:
33                w._commit_removals()
34
35
36class WeakSet:
37    def __init__(self, data=None):
38        self.data = set()
39        def _remove(item, selfref=ref(self)):
40            self = selfref()
41            if self is not None:
42                if self._iterating:
43                    self._pending_removals.append(item)
44                else:
45                    self.data.discard(item)
46        self._remove = _remove
47        # A list of keys to be removed
48        self._pending_removals = []
49        self._iterating = set()
50        if data is not None:
51            self.update(data)
52
53    def _commit_removals(self):
54        pop = self._pending_removals.pop
55        discard = self.data.discard
56        while True:
57            try:
58                item = pop()
59            except IndexError:
60                return
61            discard(item)
62
63    def __iter__(self):
64        with _IterationGuard(self):
65            for itemref in self.data:
66                item = itemref()
67                if item is not None:
68                    # Caveat: the iterator will keep a strong reference to
69                    # `item` until it is resumed or closed.
70                    yield item
71
72    def __len__(self):
73        return len(self.data) - len(self._pending_removals)
74
75    def __contains__(self, item):
76        try:
77            wr = ref(item)
78        except TypeError:
79            return False
80        return wr in self.data
81
82    def __reduce__(self):
83        return (self.__class__, (list(self),),
84                getattr(self, '__dict__', None))
85
86    def add(self, item):
87        if self._pending_removals:
88            self._commit_removals()
89        self.data.add(ref(item, self._remove))
90
91    def clear(self):
92        if self._pending_removals:
93            self._commit_removals()
94        self.data.clear()
95
96    def copy(self):
97        return self.__class__(self)
98
99    def pop(self):
100        if self._pending_removals:
101            self._commit_removals()
102        while True:
103            try:
104                itemref = self.data.pop()
105            except KeyError:
106                raise KeyError('pop from empty WeakSet') from None
107            item = itemref()
108            if item is not None:
109                return item
110
111    def remove(self, item):
112        if self._pending_removals:
113            self._commit_removals()
114        self.data.remove(ref(item))
115
116    def discard(self, item):
117        if self._pending_removals:
118            self._commit_removals()
119        self.data.discard(ref(item))
120
121    def update(self, other):
122        if self._pending_removals:
123            self._commit_removals()
124        for element in other:
125            self.add(element)
126
127    def __ior__(self, other):
128        self.update(other)
129        return self
130
131    def difference(self, other):
132        newset = self.copy()
133        newset.difference_update(other)
134        return newset
135    __sub__ = difference
136
137    def difference_update(self, other):
138        self.__isub__(other)
139    def __isub__(self, other):
140        if self._pending_removals:
141            self._commit_removals()
142        if self is other:
143            self.data.clear()
144        else:
145            self.data.difference_update(ref(item) for item in other)
146        return self
147
148    def intersection(self, other):
149        return self.__class__(item for item in other if item in self)
150    __and__ = intersection
151
152    def intersection_update(self, other):
153        self.__iand__(other)
154    def __iand__(self, other):
155        if self._pending_removals:
156            self._commit_removals()
157        self.data.intersection_update(ref(item) for item in other)
158        return self
159
160    def issubset(self, other):
161        return self.data.issubset(ref(item) for item in other)
162    __le__ = issubset
163
164    def __lt__(self, other):
165        return self.data < set(map(ref, other))
166
167    def issuperset(self, other):
168        return self.data.issuperset(ref(item) for item in other)
169    __ge__ = issuperset
170
171    def __gt__(self, other):
172        return self.data > set(map(ref, other))
173
174    def __eq__(self, other):
175        if not isinstance(other, self.__class__):
176            return NotImplemented
177        return self.data == set(map(ref, other))
178
179    def symmetric_difference(self, other):
180        newset = self.copy()
181        newset.symmetric_difference_update(other)
182        return newset
183    __xor__ = symmetric_difference
184
185    def symmetric_difference_update(self, other):
186        self.__ixor__(other)
187    def __ixor__(self, other):
188        if self._pending_removals:
189            self._commit_removals()
190        if self is other:
191            self.data.clear()
192        else:
193            self.data.symmetric_difference_update(ref(item, self._remove) for item in other)
194        return self
195
196    def union(self, other):
197        return self.__class__(e for s in (self, other) for e in s)
198    __or__ = union
199
200    def isdisjoint(self, other):
201        return len(self.intersection(other)) == 0
202
203    def __repr__(self):
204        return repr(self.data)
205
206    __class_getitem__ = classmethod(GenericAlias)
207