When I tried using `isinstance` with a type (e.g. `bool`) as the 1st argument and a parameterized generic in a tuple (e.g. '(`bool`, `list[bool]`)') as the 2nd argument, it raised a `TypeError`, 'isinstance() argument 2 cannot be a parameterized generic'. But when I did the same thing in `issubclass`, it returned a boolean and did not raise any `TypeError`s. Using `isinstance` with an object as the 1st argument and the same tuple 2nd argument also returned a boolean, and did not raise any `TypeError`s. Is this expected behaviour, or should this be fixed? This was tested in Python 3.10.0rc1 in a 64-bit system.

@Paul, Steve, Tim and Zach, I've removed y'all from nosy as this isn't a Windows issue (but a typing/builtin types one). If you feel that I shouldn't have done that: my apologies and please do tell me.

To summarize what OP said:

>>> isinstance(bool, (bool, list[bool]))
TypeError: isinstance() argument 2 cannot be a parameterized generic

>>> issubclass(bool, (bool, list[bool]))
True

@OP, this seems like a bug. issubclass should raise according to PEP 585. In this case it's short-circuiting so it doesn't check the 2nd arg. Swapping the arguments around gives the expected TypeError.

>>> issubclass(bool, (list[bool], bool))
TypeError: issubclass() argument 2 cannot be a parameterized generic

At the same time, I'm hesitant to run a check through everything in the types tuple first. That would hurt issubclass performance (I'm not sure by how much). What do you think, Guido and Serhiy?

It is not specific to typing.

>>> isinstance(1, (int, 1))
True
>>> isinstance(1, (1, int))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: isinstance() arg 2 must be a type or tuple of types
>>> issubclass(int, (int, 1))
True
>>> issubclass(int, (1, int))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: issubclass() arg 2 must be a class or tuple of classes

isinstance() and issubclass() with tuples always stopped on first positive match. I don't think there is need to change this.

Thank you for the examples Serhiy. I agree.

Agreed. Thanks, Serhiy.