isinstance doesn't work on type aliases that use a union

[DetachHead]

Foo = int | str

foo: object

isinstance(foo, Foo) # error
isinstance(foo, int | str) # no error

https://mypy-play.net/?mypy=master&python=3.10&gist=da37bef9ace54d59c18631a0a9f5bef2

[sobolevn]

I've also added explicit TypeAlias to this example, it also raises an error:

from typing import TypeAlias

A = int | str
B: TypeAlias = int | str

foo: object

isinstance(foo, A)  # error
isinstance(foo, B)  # error 
isinstance(foo, int | str)  # no error, but should be?

Output:

out/ex.py:8: error: Parameterized generics cannot be used with class or instance checks
out/ex.py:8: error: Argument 2 to "isinstance" has incompatible type "object"; expected "Union[type, UnionType, Tuple[Union[type, UnionType, Tuple[Any, ...]], ...]]"
out/ex.py:9: error: Parameterized generics cannot be used with class or instance checks
out/ex.py:9: error: Argument 2 to "isinstance" has incompatible type "object"; expected "Union[type, UnionType, Tuple[Union[type, UnionType, Tuple[Any, ...]], ...]]"

[sobolevn]

In runtime isinstance(1, int | str) works just fine:

>>> isinstance(1, int | str)
True
>>> isinstance(b'', int | str)
False

So, I guess the problem is that isinstance(foo, A) raises. In my opinion B should not be used as a value, when having explicit TypeAlias declaration.

[esoma]

Half of this is fixed in #11650

error: Parameterized generics cannot be used with class or instance checks will still occur if that is merged. It's something I looked into early on, but didn't want to complicate that PR further.

[sobolevn]

@esoma awesome! Thank you! 👍

[dgutson]

Half of this is fixed in #11650

error: Parameterized generics cannot be used with class or instance checks will still occur if that is merged. It's something I looked into early on, but didn't want to complicate that PR further.

@esoma so what's next? This is indeed still happening.
CC @qequ

[esoma]

@dgutson That PR didn't receive much attention and I don't use mypy anymore so I haven't pursued it any further.

[Gunni]

This is still broken.

error: Parameterized generics cannot be used with class or instance checks [misc]

error: Argument 2 to "isinstance" has incompatible type ""; expected "_ClassInfo" [arg-type]

import ipaddress as i
from typing import TypeAlias, TypeVar

IPAddress: TypeAlias = i.IPv4Address | i.IPv6Address
IPInterface: TypeAlias = i.IPv4Interface | i.IPv6Interface

_T = TypeVar('_T', bound=IPInterface | IPAddress)

def get_sort_key(ip: _T) -> tuple[int, IPAddress]:
	# https://github.com/python/mypy/issues/11673
	ipaddr = ip.ip if isinstance(ip, IPInterface) else ip
	return i.get_mixed_type_key(ipaddr)


def sort_ips(addresses: set[_T]) -> list[_T]:
	return sorted(addresses, key=get_sort_key)

[DetachHead]

@esoma out of curiosity, which type checker did you switch to?

[sobolevn]

The main problem is that we don't pass uses_pep604_syntax information anywhere in the code.
So, it is impossible to separate Union[str, int] from int | str later in the code, where this error happens.

[esoma]

@DetachHead
I probably should have said I generally don't use the python typing system anymore -- don't want to derail this issue with details. When I do I still use mypy.