Both `WeakKeyDictionary` and `WeakValueDictionary` have opaque `__repr__` methods:

>>> x = weakref.WeakKeyDictionary({object: 2, type: 4,})
>>> x
<WeakKeyDictionary at 0x32e6198>
>>> dict(x)
{<class 'type'>: 4, <class 'object'>: 2}

This makes it annoying to view them at a glance. Is there a reason for it? (I don't know, maybe because they're weakref? Though I'm not sure how that would affect this decision.)

If there isn't a reason, then maybe there should be a nice `__repr__` that lets you see the objects inside?