MyPy not inferring type from assert statement. about mypy HOT 5 OPEN

The following code is easier to understand for both mypy and humans:

if my_options is None:
    return MyClass(options=None)
else:
    assert isinstance(my_options.options, CustomOptions)
    return MyClass(options=my_options.options)

from mypy.

You're expecting mypy to track relationships between variables (my_options and my_options.options in your case), which it does not.

You can see another example discussed here:
https://mypy.readthedocs.io/en/stable/type_narrowing.html#limitations

p.s. @AlexWaygood maybe we need topic-entanglement :)

from mypy.

Could you provide a minimal, self-contained example? Your code sample references symbols that are not defined, which makes it difficult to diagnose what's happening here.

from mypy.

Here is a MRE, deduced from the example: https://mypy-play.net/?mypy=latest&python=3.12&gist=d7be1b77e92d1b2128b2b3492dfa3321

But you might be expecting to much from a type checker, maybe by simplifying a bit the logic you might get what you're trying to achieve

from mypy.

Thanks @Viicos , the MRE you provided perfectly describes my case. @erictraut FYI.

@Viicos what do you recommend to simplify the logic? I aimed to rely on the assert for its by-design runtime check instead of using a cast().

from mypy.