Support indexing and iterating Enum type objects

[JukkaL]

Assume this definition of Color:

from enum import Enum
class Color(Enum):
    red = 1
    green = 2
    blue = 3

Now this should be valid, but mypy complains about it:

Color['red']

The error message indicates that mypy thinks that the programmer is trying to construct a generic type, which is not the case here:

$ mypy t.py
t.py:8: error: Name 'red' is not defined

[johnthagen]

@JukkaL Another related Enum issue is that Mypy currently doesn't understand that Enum's can be iterated on.

import enum


@enum.unique
class Color(enum.Enum):
    red = 1
    green = 2
    blue = 3

for color in Color:
    print(color)

When run:

Color.red
Color.green
Color.blue

When mypy 0.4.4 is run on the file:

a.py:10: error: Iterable expected
a.py:10: error: "Color" has no attribute "__iter__"

[gvanrossum]

See also #2305.

[choucavalier]

Is someone working on this?

[gvanrossum]

Is someone working on this?

Not yet.

[JukkaL]

Increasing priority since this seems to be among the most common issues mypy users encounter.

[ilevkivskyi]

I just have tried Color['red'] and it works. The second snippet:

for color in Color:
    print(color)

still fails however.

[JukkaL]

Yes, I just noticed that myself.

[gvanrossum]

Iterating is now fix by python/typeshed#1136.

[choucavalier]

Thanks @gvanrossum! 😄

[jboning]

I'm not sure this is completely fixed: Color['red'] works, but val = Color['red'] results in the old error.

Adding an explicit annotation (val : Color = Color['red']) fixes the error and is an easy workaround, so whatever remains here is probably a lower priority to fix.

[JelleZijlstra]

From the discussion on Gitter, it seems that val = Color['red'] is interpreted as constructing a type alias.

[gvanrossum]

Could you file a new issue?

[jboning]

Forked off another issue at #3137