Support Python 3.4 Enum

[JukkaL]

This requires some special casing in the type checker.

[pbdeuchler]

Apologies if you don't want these sorts of comments, but if possible I'd love to +1 this feature... I use enums extensively and # type: ignore is making me a sad panda

[spkersten]

@pbdeuchler I can't speak for Jukka, but I like hearing that people want to use mypy.

In PR #715 I've added some very rudimentary support for Enum's. It will not check much, but should at least remove the need for the ignore annotation. Check it out if you wish, to see if it makes mypy work better on your enums.

[JukkaL]

It's always great to get feedback on which features would be useful for mypy users.

@spkersten And thanks for helping with this!

[pbdeuchler]

@spkersten looks awesome, does it have support for functionally created Enums?

[spkersten]

@pbdeuchler what are functionally created Enums? Do you have a (minimal) example?

[pbdeuchler]

A common use case for me is parsing some sort of input and creating an enum on the fly with user defined options... for example:

Color = Enum('Color', 'red orange yellow green blue indigo violet ' + ' '.join(user_input_array))

[refi64]

@pbdeuchler I don't think that's really possible without running the program.

[refi64]

@pbdeuchler I'm slightly curious how you're actually using that at runtime, though. getattr?

[berdario]

I'd really like this to work :/

The functional api is not only useful to create Enums at runtime, but it's also the simpler api that allows you to define one without having to specify superfluous values, e.g compare:

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

against

 Color = Enum('Color', 'red green blue')

At the moment, even specifying # type: ignore will yield down errors down the line when actually using the enum (forcing to litter all the code with Anys)

[JukkaL]

The form Enum('Color', 'red green blue') with all literal arguments wouldn't be very hard to support, though it's probably not going to be implemented in the next few releases at least, since there is a workaround (even if it's pretty verbose) -- unless somebody wishes to contribute an implementation :-)

[gvanrossum]

Personally I think that if you believe in static typing you should be using the full form

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

[graingert]

@gvanrossum true, I think mypy should report an error saying to write out the Enum in full.

[berdario]

Uhm, I don't quite agree:

I find Enum useful as a poor man's sum type, to detect errors earlier than by simply using string/integer constants and document all the allowed values. From this point of view there's nothing to be gained by specifying the values, because the values themselves will never be used.

It's another matter if the idea is to use it as an Enumerative to actually map something to integers (or other values).

Anyhow, reporting an error to let users know that mypy actually supports other syntaxes for Enum is surely welcome.