python - weakref.proxy 和 weakref.ref 之间的区别？

Question

来自 documentation :

Weakref.proxy returns a proxy to object which uses a weak reference. But if I run the following code:

obj = SomeObj()
obj  # <__main__.ExpensiveObject at 0xbfc5390>
p = weakref.proxy(obj)
r = weakref.ref(obj)

r() # <__main__.ExpensiveObject at 0xbfc5390>
# the weakreference gives me the same object as expected
p  # <__main__.ExpensiveObject at 0xc456098>
# the proxy refers to a different object, why is that?

任何帮助将不胜感激!谢谢!

Answer 1

您正在使用 IPython，它有自己的 pretty-print 工具。 default pretty-printer更喜欢通过 __class__ 而不是 type 来检查对象的类:

def _default_pprint(obj, p, cycle):
    """
    The default print function.  Used if an object does not provide one and
    it's none of the builtin objects.
    """
    klass = _safe_getattr(obj, '__class__', None) or type(obj)
    if _safe_getattr(klass, '__repr__', None) is not object.__repr__:
        # A user-provided repr. Find newlines and replace them with p.break_()
        _repr_pprint(obj, p, cycle)
        return
    p.begin_group(1, '<')
    p.pretty(klass)
    ...

但是 weakref.proxy 对象通过 __class__ 隐藏了它们的类，因此 pretty-print 认为代理确实是 ExpensiveObject 的一个实例.它看不到代理的 __repr__，并将类打印为 ExpensiveObject 而不是 weakproxy。