Mypy: Don't require `-> None` on `__init__`

[Daenyth]

There's no code where __init__ should return anything except None, so requiring -> None on it is just useless boilerplate.

I think it should be permitted to omit it, and that it should be inferred, as with self parameters not requiring annotation.

[ilevkivskyi]

This was already considered, see this section of PEP 484:

(Note that the return type of __init__ ought to be annotated with -> None. The reason for this is subtle. If __init__ assumed a return annotation of -> None, would that mean that an argument-less, un-annotated __init__ method should still be type-checked? Rather than leaving this ambiguous or introducing an exception to the exception, we simply say that __init__ ought to have a return annotation; the default behavior is thus the same as for other methods.)

[Daenyth]

That's reasonable. I guess I can adjust my IDE snippet to just include it

[ijstokes]

For others who end up here, it looks like this point is still open for debate in #604 (and perhaps this should be marked as a Duplicate that issue).

This quote from Guido is worth considering: https://github.com/python/mypy/issues/604#issuecomment-83887491

Hm. I think it'd suck if we'd have to develop the habit of adding explicit
"-> None" to all init methods just to make mypy happy.

I'm with him on that.

[gmolau]

Is there any way to disable this particular warning?

[gvanrossum]

@gmolau

Is there any way to disable this particular warning?

What warning? You no longer need to put a return type on __init__(), unless it has no arguments other than self.

[gmolau]

@gvanrossum Ah sorry, I was on an old mypy version. Thanks for your help!