Hi Peter, I did not know the object did not keep track of its bound methods. What advantage is there in creating a new bound method object each time its referenced? It seems kind of expensive.
Regards, Vincent -----Original Message----- From: Peter Otten [mailto:__pete...@web.de] Sent: vrijdag 30 juli 2010 15:06 To: python-list@python.org Subject: Re: The untimely dimise of a weak-reference Vincent van Beveren wrote: > Hi everyone, > > I was working with weak references in Python, and noticed that it was > impossible to create a weak-reference of bound methods. Here is a little > python 3.0 program to prove my point: > > import weakref > > print("Creating object...") > class A(object): > > def b(self): > print("I am still here") > > a = A() > > def d(r): > print("Aaah! Weakref lost ref") > > print("Creating weak reference") > > r = weakref.ref(a.b, d) The instance doesn't keep a reference of its bound method. Rather the bound method keeps a reference of its instance. Every time you say a.b you get a different bound method. What do you think should keep it alive? > print("Oh, wait, its already gone!") > print("Ref == None, cause of untimely demise: %s" % r()) > print("Object is still alive: %s" % a) > print("Function is still exists: %s" % a.b) > print("See:") > a.b() > > I also tried this in Python 2.5 and 2.6 (with minor modifications to the > syntax of course), and it yielded the exact same behavior. Why is this, > and is there anything I can do about it? I wish to reference these bound > functions, but I do not want to keep them in memory once the object they > belong to is no longer referenced. I fear you have to manage the methods' lifetime explicitly. Peter -- http://mail.python.org/mailman/listinfo/python-list
