"""
weakref_backports is a partial backport of the weakref module for python
versions below 3.4.
Copyright (C) 2013 Python Software Foundation, see license.python.txt for
details.
The following changes were made to the original sources during backporting:
* Added `self` to `super` calls.
* Removed `from None` when raising exceptions.
"""
from weakref import ref
[docs]class WeakMethod(ref):
"""
A custom `weakref.ref` subclass which simulates a weak reference to
a bound method, working around the lifetime problem of bound methods.
"""
__slots__ = "_func_ref", "_meth_type", "_alive", "__weakref__"
def __new__(cls, meth, callback=None):
try:
obj = meth.__self__
func = meth.__func__
except AttributeError:
raise TypeError("argument should be a bound method, not {}"
.format(type(meth)))
def _cb(arg):
# The self-weakref trick is needed to avoid creating a reference
# cycle.
self = self_wr()
if self._alive:
self._alive = False
if callback is not None:
callback(self)
self = ref.__new__(cls, obj, _cb)
self._func_ref = ref(func, _cb)
self._meth_type = type(meth)
self._alive = True
self_wr = ref(self)
return self
def __call__(self):
obj = super(WeakMethod, self).__call__()
func = self._func_ref()
if obj is None or func is None:
return None
return self._meth_type(func, obj)
def __eq__(self, other):
if isinstance(other, WeakMethod):
if not self._alive or not other._alive:
return self is other
return ref.__eq__(self, other) and self._func_ref == other._func_ref
return False
def __ne__(self, other):
if isinstance(other, WeakMethod):
if not self._alive or not other._alive:
return self is not other
return ref.__ne__(self, other) or self._func_ref != other._func_ref
return True
__hash__ = ref.__hash__