664 lines
21 KiB
Python
664 lines
21 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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_remove_dead_weakref)
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from _weakrefset import WeakSet, _IterationGuard
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import _collections_abc # Import after _weakref to avoid circular import.
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import sys
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import itertools
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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", "WeakMethod", "finalize"]
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class WeakMethod(ref):
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"""
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A custom `weakref.ref` subclass which simulates a weak reference to
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a bound method, working around the lifetime problem of bound methods.
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"""
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__slots__ = "_func_ref", "_meth_type", "_alive", "__weakref__"
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def __new__(cls, meth, callback=None):
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try:
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obj = meth.__self__
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func = meth.__func__
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except AttributeError:
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raise TypeError("argument should be a bound method, not {}"
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.format(type(meth))) from None
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def _cb(arg):
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# The self-weakref trick is needed to avoid creating a reference
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# cycle.
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self = self_wr()
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if self._alive:
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self._alive = False
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if callback is not None:
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callback(self)
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self = ref.__new__(cls, obj, _cb)
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self._func_ref = ref(func, _cb)
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self._meth_type = type(meth)
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self._alive = True
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self_wr = ref(self)
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return self
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def __call__(self):
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obj = super().__call__()
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func = self._func_ref()
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if obj is None or func is None:
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return None
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return self._meth_type(func, obj)
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def __eq__(self, other):
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if isinstance(other, WeakMethod):
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if not self._alive or not other._alive:
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return self is other
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return ref.__eq__(self, other) and self._func_ref == other._func_ref
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return False
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def __ne__(self, other):
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if isinstance(other, WeakMethod):
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if not self._alive or not other._alive:
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return self is not other
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return ref.__ne__(self, other) or self._func_ref != other._func_ref
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return True
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__hash__ = ref.__hash__
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class WeakValueDictionary(_collections_abc.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__(*args, **kw):
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if not args:
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raise TypeError("descriptor '__init__' of 'WeakValueDictionary' "
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"object needs an argument")
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self, *args = args
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if len(args) > 1:
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raise TypeError('expected at most 1 arguments, got %d' % len(args))
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def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref):
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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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# Atomic removal is necessary since this function
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# can be called asynchronously by the GC
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_atomic_removal(d, 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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key = l.pop()
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_remove_dead_weakref(d, key)
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def __getitem__(self, key):
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if self._pending_removals:
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self._commit_removals()
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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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if self._pending_removals:
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self._commit_removals()
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return len(self.data)
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def __contains__(self, key):
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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[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 "<%s at %#x>" % (self.__class__.__name__, 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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if self._pending_removals:
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self._commit_removals()
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new = WeakValueDictionary()
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with _IterationGuard(self):
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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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if self._pending_removals:
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self._commit_removals()
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new = self.__class__()
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with _IterationGuard(self):
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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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if self._pending_removals:
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self._commit_removals()
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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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if self._pending_removals:
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self._commit_removals()
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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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if self._pending_removals:
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self._commit_removals()
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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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if self._pending_removals:
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self._commit_removals()
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with _IterationGuard(self):
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yield from self.data.values()
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def values(self):
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if self._pending_removals:
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self._commit_removals()
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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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o = None
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if o is None:
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if args:
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return args[0]
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else:
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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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o = self.data[key]()
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except KeyError:
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o = None
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if o is None:
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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 o
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def update(*args, **kwargs):
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if not args:
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raise TypeError("descriptor 'update' of 'WeakValueDictionary' "
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"object needs an argument")
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self, *args = args
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if len(args) > 1:
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raise TypeError('expected at most 1 arguments, got %d' % len(args))
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dict = args[0] if args else None
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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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if self._pending_removals:
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self._commit_removals()
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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_abc.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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self._dirty_len = False
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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 _scrub_removals(self):
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d = self.data
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self._pending_removals = [k for k in self._pending_removals if k in d]
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self._dirty_len = False
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def __delitem__(self, key):
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self._dirty_len = True
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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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if self._dirty_len and self._pending_removals:
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# self._pending_removals may still contain keys which were
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# explicitly removed, we have to scrub them (see issue #21173).
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self._scrub_removals()
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return len(self.data) - len(self._pending_removals)
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def __repr__(self):
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return "<%s at %#x>" % (self.__class__.__name__, 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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with _IterationGuard(self):
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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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with _IterationGuard(self):
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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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|
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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.
|
|
|
|
The references are not guaranteed to be 'live' at the time
|
|
they are used, so the result of calling the references needs
|
|
to be checked before being used. This can be used to avoid
|
|
creating references that will cause the garbage collector to
|
|
keep the keys around longer than needed.
|
|
|
|
"""
|
|
return list(self.data)
|
|
|
|
def popitem(self):
|
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self._dirty_len = True
|
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while True:
|
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key, value = self.data.popitem()
|
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o = key()
|
|
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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self._dirty_len = True
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return self.data.pop(ref(key), *args)
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|
|
|
def setdefault(self, key, default=None):
|
|
return self.data.setdefault(ref(key, self._remove),default)
|
|
|
|
def update(self, dict=None, **kwargs):
|
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d = self.data
|
|
if dict is not None:
|
|
if not hasattr(dict, "items"):
|
|
dict = type({})(dict)
|
|
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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|
|
|
|
|
class finalize:
|
|
"""Class for finalization of weakrefable objects
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|
|
|
finalize(obj, func, *args, **kwargs) returns a callable finalizer
|
|
object which will be called when obj is garbage collected. The
|
|
first time the finalizer is called it evaluates func(*arg, **kwargs)
|
|
and returns the result. After this the finalizer is dead, and
|
|
calling it just returns None.
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|
|
|
When the program exits any remaining finalizers for which the
|
|
atexit attribute is true will be run in reverse order of creation.
|
|
By default atexit is true.
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|
"""
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|
|
|
# Finalizer objects don't have any state of their own. They are
|
|
# just used as keys to lookup _Info objects in the registry. This
|
|
# ensures that they cannot be part of a ref-cycle.
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|
|
|
__slots__ = ()
|
|
_registry = {}
|
|
_shutdown = False
|
|
_index_iter = itertools.count()
|
|
_dirty = False
|
|
_registered_with_atexit = False
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|
|
|
class _Info:
|
|
__slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index")
|
|
|
|
def __init__(*args, **kwargs):
|
|
if len(args) >= 3:
|
|
self, obj, func, *args = args
|
|
elif not args:
|
|
raise TypeError("descriptor '__init__' of 'finalize' object "
|
|
"needs an argument")
|
|
else:
|
|
if 'func' not in kwargs:
|
|
raise TypeError('finalize expected at least 2 positional '
|
|
'arguments, got %d' % (len(args)-1))
|
|
func = kwargs.pop('func')
|
|
if len(args) >= 2:
|
|
self, obj, *args = args
|
|
import warnings
|
|
warnings.warn("Passing 'func' as keyword argument is deprecated",
|
|
DeprecationWarning, stacklevel=2)
|
|
else:
|
|
if 'obj' not in kwargs:
|
|
raise TypeError('finalize expected at least 2 positional '
|
|
'arguments, got %d' % (len(args)-1))
|
|
obj = kwargs.pop('obj')
|
|
self, *args = args
|
|
import warnings
|
|
warnings.warn("Passing 'obj' as keyword argument is deprecated",
|
|
DeprecationWarning, stacklevel=2)
|
|
args = tuple(args)
|
|
|
|
if not self._registered_with_atexit:
|
|
# We may register the exit function more than once because
|
|
# of a thread race, but that is harmless
|
|
import atexit
|
|
atexit.register(self._exitfunc)
|
|
finalize._registered_with_atexit = True
|
|
info = self._Info()
|
|
info.weakref = ref(obj, self)
|
|
info.func = func
|
|
info.args = args
|
|
info.kwargs = kwargs or None
|
|
info.atexit = True
|
|
info.index = next(self._index_iter)
|
|
self._registry[self] = info
|
|
finalize._dirty = True
|
|
__init__.__text_signature__ = '($self, obj, func, /, *args, **kwargs)'
|
|
|
|
def __call__(self, _=None):
|
|
"""If alive then mark as dead and return func(*args, **kwargs);
|
|
otherwise return None"""
|
|
info = self._registry.pop(self, None)
|
|
if info and not self._shutdown:
|
|
return info.func(*info.args, **(info.kwargs or {}))
|
|
|
|
def detach(self):
|
|
"""If alive then mark as dead and return (obj, func, args, kwargs);
|
|
otherwise return None"""
|
|
info = self._registry.get(self)
|
|
obj = info and info.weakref()
|
|
if obj is not None and self._registry.pop(self, None):
|
|
return (obj, info.func, info.args, info.kwargs or {})
|
|
|
|
def peek(self):
|
|
"""If alive then return (obj, func, args, kwargs);
|
|
otherwise return None"""
|
|
info = self._registry.get(self)
|
|
obj = info and info.weakref()
|
|
if obj is not None:
|
|
return (obj, info.func, info.args, info.kwargs or {})
|
|
|
|
@property
|
|
def alive(self):
|
|
"""Whether finalizer is alive"""
|
|
return self in self._registry
|
|
|
|
@property
|
|
def atexit(self):
|
|
"""Whether finalizer should be called at exit"""
|
|
info = self._registry.get(self)
|
|
return bool(info) and info.atexit
|
|
|
|
@atexit.setter
|
|
def atexit(self, value):
|
|
info = self._registry.get(self)
|
|
if info:
|
|
info.atexit = bool(value)
|
|
|
|
def __repr__(self):
|
|
info = self._registry.get(self)
|
|
obj = info and info.weakref()
|
|
if obj is None:
|
|
return '<%s object at %#x; dead>' % (type(self).__name__, id(self))
|
|
else:
|
|
return '<%s object at %#x; for %r at %#x>' % \
|
|
(type(self).__name__, id(self), type(obj).__name__, id(obj))
|
|
|
|
@classmethod
|
|
def _select_for_exit(cls):
|
|
# Return live finalizers marked for exit, oldest first
|
|
L = [(f,i) for (f,i) in cls._registry.items() if i.atexit]
|
|
L.sort(key=lambda item:item[1].index)
|
|
return [f for (f,i) in L]
|
|
|
|
@classmethod
|
|
def _exitfunc(cls):
|
|
# At shutdown invoke finalizers for which atexit is true.
|
|
# This is called once all other non-daemonic threads have been
|
|
# joined.
|
|
reenable_gc = False
|
|
try:
|
|
if cls._registry:
|
|
import gc
|
|
if gc.isenabled():
|
|
reenable_gc = True
|
|
gc.disable()
|
|
pending = None
|
|
while True:
|
|
if pending is None or finalize._dirty:
|
|
pending = cls._select_for_exit()
|
|
finalize._dirty = False
|
|
if not pending:
|
|
break
|
|
f = pending.pop()
|
|
try:
|
|
# gc is disabled, so (assuming no daemonic
|
|
# threads) the following is the only line in
|
|
# this function which might trigger creation
|
|
# of a new finalizer
|
|
f()
|
|
except Exception:
|
|
sys.excepthook(*sys.exc_info())
|
|
assert f not in cls._registry
|
|
finally:
|
|
# prevent any more finalizers from executing during shutdown
|
|
finalize._shutdown = True
|
|
if reenable_gc:
|
|
gc.enable()
|