mypy Type error for a class with an imported metaclass

[seanp2]

Please provide more information to help us understand the issue:

• Are you reporting a bug, or opening a feature request? bug
• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.
  Here is an example class I am working with.

@enum.unique
class MyEnumClass(Enum, metaclass=MyEnumMetaClass):
    OUT_OF_STOCK = "Out of Stock"
    LOW_STOCK = "Low Stock"
    IN_STOCK = "In Stock"
    EXCESS = "Excess"

I am making a change where I am importing the MyEnumMetaClass class from a PIP package now, whereas before it was located within the same project as this class.

• What is the actual behavior/output?
  With MyEnumMetaClass imported, whenever I create a MyEnumClass instance, mypy gives me the following error:
  error: The type "Type[MyEnumClass]" is not generic and not indexable
• What is the behavior/output you expect?
  I expect mypy to succeed here, given that the code is the same, it is just imported from a package now.

[ilevkivskyi]

I think this is a bug, mypy is likely confused by the custom metaclass and doesn't apply the usual enum special-casing. Likely this is easy to fix. The relevant code is in semanal.py (look where is_enum flag on TypeInfo is set).

[gvanrossum]

I am making a change where I am importing the MyEnumMetaClass class from a PIP package now, whereas before it was located within the same project as this class.

This may be key. Is there a stub for that pip package? Or does it have a py.typed marker per PEP 561? If neither is the case, mypy doesn't read the types from the package and assumes the metaclass is Any.

[ilevkivskyi]

If neither is the case, mypy doesn't read the types from the package and assumes the metaclass is Any.

If the Enum base in the example is the stdlib Enum I think we should apply enum special-casing even if the metaclass is Any.

[Kaushal-Dhungel]

hey @ilevkivskyi . Seems like this issue is still open. Can I take it??

[ilevkivskyi]

@Kaushal-Dhungel sure, go head.

[Soumokanti123]

@Kaushal-Dhungel sure, go head.

Hi sir, Can I take it to solve the problem?

[Hyperion101010]

Hi there I am Shivam, I know Python to an intermediate level,
I am interested to solve this issue, will you assign me?

[JukkaL]

@Hyperion101010 Done!

[saru-d2]

Hi, just curious if the issue is being solved/ has been solved, if not I'd love to give it a shot!

[SwagatSBhuyan]

I'd like to tackle this issue.
@seanp2 if you'd be kind enough to maybe make me reproduce this error, that'd be great! And I also have a few more doubts so if anyone could get back to me that'd be really helpful, as I am new to contributing.
@ilevkivskyi @JukkaL @gvanrossum
Thanks!

[Netaliyev]

Hi there, I have been trying to contribute to mypy for weeks, but I am intermediate in the Python. I was trying to understand the code in the semanal.py, but it is hard to understand where the problem is. Can you give me tips where should I look so I can try to solve this issue?

[quinnah]

Hi there - I'd like to try my hand at this issue. @ilevkivskyi @JukkaL could I claim this issue?

[ilevkivskyi]

@quinnah Yes, sure, you can give it a try.

[quinnah]

Hey @ilevkivskyi, sorry I don't think I'll have time to work on this :/

[ilevkivskyi]

OK, NP