Pablo Galindo Salgado <[email protected]> added the comment:
In my view, proxies should behave almost exactly as the underliying object, so
using them is as ergonomic as possible. For instance, when using them as a way
to avoid cycles, is quite annoying if you have a hashable object in a
dictionary and they fail to tell you that is there:
>>> class A:
... ...
...
>>> a = A()
>>> d = {a: None}
>>> weakref.proxy(a) in d
True
but doing this in 3.8 is impossible:
>>> import weakref
>>> class A:
... ...
...
>>> a = A()
>>> d = {a: None}
>>> weakref.proxy(a) in d
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'weakproxy'
Which defies a lot of use cases of this. Notice that if the object is not
hashable because the author of the class wants to prevent against that it will
work as expected:
>>> class A:
... __hash__ = None
...
>>> a = A()
>>> hash(weakref.proxy(a))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'A'
This also gives a better error message because it explains that A is not
hashable.
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<https://bugs.python.org/issue44523>
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