Cem Karan wrote: > > On Feb 21, 2015, at 12:27 PM, Steven D'Aprano > <steve+comp.lang.pyt...@pearwood.info> wrote:
>> The simplest possible identity-based scheme would be something like this: >> >> >> # don't hate me for using a global variable >> CALLBACKS = [] >> >> def register(func): >> if func not in CALLBACKS: >> CALLBACKS.append(func) >> >> def unregister(func): >> try: >> CALLBACKS.remove(func) >> except ValueError: >> pass Oops! That's not identity-based, that's *equality* based. Both the `in` operator and the list `remove` method implicitly perform equality checks, not identity checks. Which means that they will work with methods, since method equality compares against the underlying function, which is the same: py> class Spam(object): ... def method(self): ... pass ... py> s = Spam() py> a = s.method py> b = s.method py> a is b False py> a == b True py> a.__func__ is b.__func__ True So, when I say this: >> That's probably a bit too simple, since it won't behave as expected with >> bound methods. The problem is that bound methods are generated on the >> fly, so this won't work: I was mistaken. > Are you sure about that? I just tested out the following code, and it > appears to work correctly: You are correct. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
