Compatibility issues between base and C-accelerated pyyaml types

[masklinn]

pyyaml does not implicitly swap out the C-accelerated types for the base ones because there are observable differences between the two (yaml/pyyaml#436).

However for packages only expected relatively simple inputs, a common pattern is to try and use the libYAML types if available and fallback:

try:
    from yaml import CLoader as Loader
except ImportError:
    from yaml import Loader

However running this through mypy yields:

error: Incompatible import of "Loader" (imported name has type "Type[Loader]", local name has type "Type[CLoader]")

While this is technically correct, it's not exactly convenient. Is there a local workaround aside from type: ignore, or a way to fix this in the stubs?

Tested with:

• CPython 10.4
• mypy 0.950
• types_PyYAML 6.0.7

[JelleZijlstra]

I don't think we can fix this in typeshed. I believe there are already some mypy issues about this pattern.

[AlexWaygood]

I don't think we can fix this in typeshed. I believe there are already some mypy issues about this pattern.

• mypy bug with try/except conditional imports mypy#1153 for one

[Akuli]

Is there a local workaround aside from type: ignore

Yes, but it's much uglier than # type: ignore:

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from yaml import Loader
else:
    try:
        from yaml import CLoader as Loader
    except ImportError:
        from yaml import Loader