On Oct 2, 2009, at 1:54 AM, Ole Streicher wrote:
I am trying to use a weak reference to a bound method:
class MyClass(object):
def myfunc(self):
pass
o = MyClass()
print o.myfunc
<bound method MyClass.myfunc of <__main__.MyClass object at
0xc675d0>>
import weakref
r = weakref.ref(o.myfunc)
print r()
None
This is what I do not understand. The object "o" is still alive, and
therefore the bound method "o.myfunc" shall exists.
Like Peter said, bound methods are created on demand when they are
obtained from the instance, not when the instance is created.
Why does the weak reference claim that it is removed? And how can I
hold
the reference to the method until the object is removed?
You could combine unbound methods with a weakref to the object:
r = weakref.ref(o)
MyClass.myfunc(r())
You could also create a wrapper object that holds a weak reference to
the instance and creates a bound method on demand:
class WeakMethod(object):
def __init__(self, bound_method):
self.im_func = bound_method.im_func
self.im_self = weakref.ref(bound_method.im_self)
self.im_class = bound_method.im_class
def __call__(self):
obj = self.im_self()
if obj is None: return None
return types.MethodType(self.im_func, obj, self.im_class)
# could alternately act like a callableproxy
-Miles
--
http://mail.python.org/mailman/listinfo/python-list
