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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 | # weak.py
#
# Copyright (C) 2004 Daniel Burrows <dburrows@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
# This file contains code to work around a leak in the Python weak
# reference abstraction.
import weakref
def WeakCallableRef(f, callback=lambda *args:None):
"""This works around a Python bug: bound methods are instantiated
as tuple-like objects that point to the object, so a weak
reference to a bound method dies instantly.
A WeakCallableRef holds a weak reference to both an object and its
method, and \"dies\" at exactly the same time as the object. The
routine callback is invoked when the object dies."""
class WeakWrapper:
"""This wraps the transient method object."""
def __init__(self, obj, method):
self.obj=weakref.ref(obj, self.__kill)
self.method=method
def __kill(self, deadman):
self.method=lambda *args:None
callback(self)
def __call__(self, *args):
obj=self.obj()
if obj == None:
return None
else:
return lambda *args:apply(self.method, (obj,)+args)
# Is it a method?
try:
f.im_self
except AttributeError:
# No, so the bug doesn't apply; use a standard weak reference.
return weakref.ref(f, callback)
# Ok, return a true wrapper.
return WeakWrapper(f.im_self, f.im_func)
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