weakrefs and bound methods

[Mathias Panzenboeck]

Marc 'BlackJack' Rintsch wrote:
> On Sun, 07 Oct 2007 16:51:33 +0200, Mathias Panzenboeck wrote:
> 
>> import weakref
>>
>> class Wrapper(object):
>> 	def __init__(self,x):
>> 		self.x = weakref.ref(x)
>>
>> 	def __call__(self,*args,**kwargs):
>> 		x = self.x()
>> 		if x is None:
>> 			print "lost reference"
>> 		else:
>> 			return x(*args,**kwargs)
>>
>> class Foo(object):
>> 	def __init__(self):
>> 		self._methods = set()
>> 		self._methods.add(Wrapper(self._foo))
>>
>> 	def _foo(self):
>> 		print "_foo"
>>
>> 	def callMethods(self):
>> 		for method in self._methods:
>> 			method()
>>
>> 	def __del__(self):
>> 		print "del Foo"
>>
>> class Bar(object):
>> 	def __init__(self):
>> 		self._methods = set()
>> 		self._methods.add(self._foo)
>>
>> 	def _foo(self):
>> 		print "_foo"
>>
>> 	def callMethods(self):
>> 		for method in self._methods:
>> 			method()
>>
>> 	def __del__(self):
>> 		print "del Bar"
>>
>>
>>
>> Now look what happens when I do this:
>>
>>>>> f=Foo()
>>>>> f.callMethods()
>> lost reference
>>>>> del f
>> del Foo
>>>>> b=Bar()
>>>>> b.callMethods()
>> _foo
>>>>> del b
>>>>>
>> Foo looses the reference to its method but Bar on the other hand has a refloop and
>> never gets deleted.
> 
> ``del b`` just deletes the name `b`.  It does not delete the object. 
> There's still the name `_` bound to it in the interactive interpreter. 
> `_` stays bound to the last non-`None` result in the interpreter.
> 

Why is it then that f (instance of Foo) really gets deleted? (__del__ is called)

> Drop all those `__del__()` methods as they prevent the garbage collector
> from collecting "cycles".
> 
> Ciao,
> 	Marc 'BlackJack' Rintsch

I only inserted them so I can see if the objects are really freed. How can I see that
without a __del__ method?


Thanks so far,
panzi