从python中的weakref代理获取常规引用

Question

Is there a way to get a proper reference for an object for which I get a weakref proxy?

I've gone through the weakref module's documentation and coulnd't get an answer there, or through poking a weakproxy object manually.

Answer 1

Although there's nothing exposed directly on the proxy object itself, it is possible to obtain a reference by abusing the __self__ attribute of bound methods:

obj_ref = proxy.__repr__.__self__

Using __repr__ here is just a random choice, although if you want a generic method it'd be better to use a method that all objects should have.

Answer 2

You can get the referent from a weakref object by calling it:

obj = ref()

From the weakref docs :

Weak reference objects have no attributes or methods, but do allow the referent to be obtained, if it still exists, by calling it. If the referent no longer exists, calling the reference object returns None .

This doesn't work for proxy objects though, and I don't see a way to get to a weak reference object or a reference to the actual object from a weakref proxy.

Answer 3

I don't know what you mean by a proper reference, but according to: https://pymotw.com/2/weakref/ ,

you can just use the proxy as if you would use the original object.

import weakref

class ExpensiveObject(object):
    def __init__(self, name):
        self.name = name
    def __del__(self):
        print '(Deleting %s)' % self

obj = ExpensiveObject('My Object')
r = weakref.ref(obj)
p = weakref.proxy(obj)

print 'via obj:', obj.name
print 'via ref:', r().name
print 'via proxy:', p.name
del obj
print 'via proxy:', p.name

This contrasts to using weakref.ref, where you have to call, ie use the ()-operator on, the weak reference to get to the original object.