Python __iter__ 和 __getattr__ 行为

Question

Trying to build something and found this odd behavior. I'm trying to build a class that I can call dict on

class Test1:
    def __iter__(self):
        return iter([(a, a) for a in range(10)])

obj = Test1()
dict(obj)  # returns {0: 0, 1: 1, 2: 2 ...}

now in my use case the object has a __getattr__ overload, which is where the problem comes in so

class Test2:
    def __iter__(self):
        return iter([(a, a) for a in range(10)])

    def __getattr__(self, attr):
        raise Exception(f"why are you calling me {attr}")

obj = Test2()
dict(obj)  # Exception: why are you calling me keys

The dict function is calling somewhere self.keys but obviously Test1().keys throws an AttributeError so it's being handed there somehow. How do I get __iter__ and __getattr__ to play nicely together. Or is there a better way of doing this?

Edit:

I guess raising an AttributeError works

class Test2:
    def __iter__(self):
        return iter([(a, a) for a in range(10)])

    def __getattr__(self, attr):
        raise AttributeError(f"why are you calling me {attr}")

obj = Test2()
dict(obj). # No Exception

Answer 1

You don't actually have to PROVIDE .keys (clearly, or your first example would have failed). You just need to provide the right exception. This works:

class Test2:
    def __iter__(self):
        return iter([(a, a) for a in range(10)])

    def __getattr__(self, attr):
        if attr == 'keys':
            raise AttributeError(f"{type(self).__name__!r} object has no attribute {attr!r}")
        raise Exception(f"why are you calling me {attr}")

obj = Test2()
dict(obj)  # Exception: why are you calling me keys