386 lines
11 KiB
Python
386 lines
11 KiB
Python
"""Weak reference support for Python.
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This module is an implementation of PEP 205:
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http://www.python.org/dev/peps/pep-0205/
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"""
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# Naming convention: Variables named "wr" are weak reference objects;
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# they are called this instead of "ref" to avoid name collisions with
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# the module-global ref() function imported from _weakref.
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from _weakref import (
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getweakrefcount,
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getweakrefs,
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ref,
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proxy,
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CallableProxyType,
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ProxyType,
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ReferenceType)
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from _weakrefset import WeakSet, _IterationGuard
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import collections # Import after _weakref to avoid circular import.
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ProxyTypes = (ProxyType, CallableProxyType)
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__all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",
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"WeakKeyDictionary", "ReferenceType", "ProxyType",
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"CallableProxyType", "ProxyTypes", "WeakValueDictionary",
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"WeakSet"]
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class WeakValueDictionary(collections.MutableMapping):
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"""Mapping class that references values weakly.
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Entries in the dictionary will be discarded when no strong
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reference to the value exists anymore
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"""
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# We inherit the constructor without worrying about the input
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# dictionary; since it uses our .update() method, we get the right
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# checks (if the other dictionary is a WeakValueDictionary,
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# objects are unwrapped on the way out, and we always wrap on the
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# way in).
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def __init__(self, *args, **kw):
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def remove(wr, selfref=ref(self)):
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self = selfref()
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if self is not None:
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if self._iterating:
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self._pending_removals.append(wr.key)
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else:
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del self.data[wr.key]
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self._remove = remove
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# A list of keys to be removed
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self._pending_removals = []
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self._iterating = set()
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self.data = d = {}
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self.update(*args, **kw)
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def _commit_removals(self):
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l = self._pending_removals
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d = self.data
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# We shouldn't encounter any KeyError, because this method should
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# always be called *before* mutating the dict.
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while l:
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del d[l.pop()]
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def __getitem__(self, key):
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o = self.data[key]()
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if o is None:
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raise KeyError(key)
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else:
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return o
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def __delitem__(self, key):
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if self._pending_removals:
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self._commit_removals()
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del self.data[key]
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def __len__(self):
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return sum(wr() is not None for wr in self.data.values())
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def __contains__(self, key):
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try:
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o = self.data[key]()
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except KeyError:
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return False
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return o is not None
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def __repr__(self):
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return "<WeakValueDictionary at %s>" % id(self)
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def __setitem__(self, key, value):
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if self._pending_removals:
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self._commit_removals()
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self.data[key] = KeyedRef(value, self._remove, key)
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def copy(self):
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new = WeakValueDictionary()
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for key, wr in self.data.items():
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o = wr()
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if o is not None:
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new[key] = o
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return new
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__copy__ = copy
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def __deepcopy__(self, memo):
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from copy import deepcopy
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new = self.__class__()
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for key, wr in self.data.items():
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o = wr()
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if o is not None:
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new[deepcopy(key, memo)] = o
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return new
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def get(self, key, default=None):
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try:
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wr = self.data[key]
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except KeyError:
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return default
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else:
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o = wr()
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if o is None:
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# This should only happen
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return default
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else:
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return o
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def items(self):
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with _IterationGuard(self):
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for k, wr in self.data.items():
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v = wr()
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if v is not None:
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yield k, v
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def keys(self):
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with _IterationGuard(self):
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for k, wr in self.data.items():
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if wr() is not None:
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yield k
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__iter__ = keys
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def itervaluerefs(self):
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"""Return an iterator that yields the weak references to the values.
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The references are not guaranteed to be 'live' at the time
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they are used, so the result of calling the references needs
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to be checked before being used. This can be used to avoid
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creating references that will cause the garbage collector to
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keep the values around longer than needed.
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"""
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with _IterationGuard(self):
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for wr in self.data.values():
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yield wr
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def values(self):
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with _IterationGuard(self):
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for wr in self.data.values():
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obj = wr()
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if obj is not None:
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yield obj
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def popitem(self):
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if self._pending_removals:
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self._commit_removals()
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while True:
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key, wr = self.data.popitem()
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o = wr()
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if o is not None:
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return key, o
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def pop(self, key, *args):
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if self._pending_removals:
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self._commit_removals()
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try:
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o = self.data.pop(key)()
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except KeyError:
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if args:
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return args[0]
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raise
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if o is None:
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raise KeyError(key)
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else:
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return o
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def setdefault(self, key, default=None):
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try:
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wr = self.data[key]
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except KeyError:
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if self._pending_removals:
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self._commit_removals()
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self.data[key] = KeyedRef(default, self._remove, key)
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return default
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else:
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return wr()
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def update(self, dict=None, **kwargs):
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if self._pending_removals:
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self._commit_removals()
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d = self.data
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if dict is not None:
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if not hasattr(dict, "items"):
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dict = type({})(dict)
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for key, o in dict.items():
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d[key] = KeyedRef(o, self._remove, key)
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if len(kwargs):
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self.update(kwargs)
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def valuerefs(self):
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"""Return a list of weak references to the values.
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The references are not guaranteed to be 'live' at the time
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they are used, so the result of calling the references needs
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to be checked before being used. This can be used to avoid
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creating references that will cause the garbage collector to
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keep the values around longer than needed.
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"""
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return list(self.data.values())
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class KeyedRef(ref):
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"""Specialized reference that includes a key corresponding to the value.
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This is used in the WeakValueDictionary to avoid having to create
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a function object for each key stored in the mapping. A shared
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callback object can use the 'key' attribute of a KeyedRef instead
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of getting a reference to the key from an enclosing scope.
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"""
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__slots__ = "key",
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def __new__(type, ob, callback, key):
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self = ref.__new__(type, ob, callback)
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self.key = key
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return self
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def __init__(self, ob, callback, key):
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super().__init__(ob, callback)
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class WeakKeyDictionary(collections.MutableMapping):
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""" Mapping class that references keys weakly.
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Entries in the dictionary will be discarded when there is no
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longer a strong reference to the key. This can be used to
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associate additional data with an object owned by other parts of
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an application without adding attributes to those objects. This
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can be especially useful with objects that override attribute
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accesses.
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"""
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def __init__(self, dict=None):
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self.data = {}
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def remove(k, selfref=ref(self)):
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self = selfref()
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if self is not None:
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if self._iterating:
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self._pending_removals.append(k)
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else:
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del self.data[k]
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self._remove = remove
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# A list of dead weakrefs (keys to be removed)
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self._pending_removals = []
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self._iterating = set()
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if dict is not None:
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self.update(dict)
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def _commit_removals(self):
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# NOTE: We don't need to call this method before mutating the dict,
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# because a dead weakref never compares equal to a live weakref,
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# even if they happened to refer to equal objects.
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# However, it means keys may already have been removed.
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l = self._pending_removals
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d = self.data
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while l:
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try:
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del d[l.pop()]
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except KeyError:
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pass
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def __delitem__(self, key):
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del self.data[ref(key)]
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def __getitem__(self, key):
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return self.data[ref(key)]
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def __len__(self):
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return len(self.data)
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def __repr__(self):
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return "<WeakKeyDictionary at %s>" % id(self)
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def __setitem__(self, key, value):
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self.data[ref(key, self._remove)] = value
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def copy(self):
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new = WeakKeyDictionary()
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for key, value in self.data.items():
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o = key()
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if o is not None:
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new[o] = value
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return new
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__copy__ = copy
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def __deepcopy__(self, memo):
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from copy import deepcopy
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new = self.__class__()
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for key, value in self.data.items():
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o = key()
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if o is not None:
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new[o] = deepcopy(value, memo)
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return new
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def get(self, key, default=None):
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return self.data.get(ref(key),default)
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def __contains__(self, key):
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try:
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wr = ref(key)
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except TypeError:
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return False
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return wr in self.data
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def items(self):
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with _IterationGuard(self):
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for wr, value in self.data.items():
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key = wr()
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if key is not None:
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yield key, value
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def keys(self):
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with _IterationGuard(self):
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for wr in self.data:
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obj = wr()
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if obj is not None:
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yield obj
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__iter__ = keys
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def values(self):
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with _IterationGuard(self):
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for wr, value in self.data.items():
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if wr() is not None:
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yield value
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def keyrefs(self):
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"""Return a list of weak references to the keys.
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The references are not guaranteed to be 'live' at the time
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they are used, so the result of calling the references needs
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to be checked before being used. This can be used to avoid
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creating references that will cause the garbage collector to
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keep the keys around longer than needed.
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"""
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return list(self.data)
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def popitem(self):
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while True:
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key, value = self.data.popitem()
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o = key()
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if o is not None:
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return o, value
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def pop(self, key, *args):
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return self.data.pop(ref(key), *args)
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def setdefault(self, key, default=None):
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return self.data.setdefault(ref(key, self._remove),default)
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def update(self, dict=None, **kwargs):
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d = self.data
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if dict is not None:
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if not hasattr(dict, "items"):
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dict = type({})(dict)
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for key, value in dict.items():
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d[ref(key, self._remove)] = value
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if len(kwargs):
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self.update(kwargs)
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