This seems pretty reasonable to me, and could be a good starter task for someone looking to get their hands dirty.

Of the two proposed syntaxes, I'd vastly prefer the second one (# type: (...) -> ReturnType), because the first would require special casing in the parser (and there's no point in doing that when the second syntax is fine).

@gvanrossum would this require a change to PEP 484?

(I'd actually love to jump on this task myself, once the powers that be give it the OK!)

Yes, it would require a PEP change. But go ahead and make a PR.

--Guido (mobile)
On Feb 22, 2016 5:28 PM, "Max Wittek" [email protected] wrote:

(I'd actually love to jump on this task myself, once the powers that be
give it the OK!)

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Here's a good place to start: https://github.com/python/mypy/blob/master/mypy/parse.py#L404

Note that in Python 3 this is already possible by omitting argument type annotations. For example:

def f(a, b) -> int:
    ...

This proposal brings Python 2 syntax closer to Python 3, which is good. Mixing annotated and unannotated arguments in a single function won't be supported for Python 2, but I'd argue that it's a marginal need.

Agreed. Also, aren't unannotated arguments treated equivalently to arguments annotated with Any? So putting Anys in Python 2 annotations is the same as leaving them unannotated in Python 3 (from a type checking perspective).

Right. I was just responding to Jukka's point about mixing annotated and unannotated arguments in a single function.

I cross-filed this for PyCharm: https://youtrack.jetbrains.com/issue/PY-18598

And if python/typing#186 gets accepted, this would make the syntax even closer to the Python 3 syntax in terms of supported features. I assume that this would be okay:

def f(x,  # type: int
      y):
    # type: (...) -> str
    # Note that only x has an annotation, y has an implicit Any type
    ...

Yes.

--Guido (mobile)
On Mar 2, 2016 10:42 AM, "Jukka Lehtosalo" [email protected] wrote:

And if python/typing#186 python/typing#186
gets accepted, this would make the syntax even closer to the Python 3
syntax in terms of supported features. I assume that this would be okay:

def f(x, # type: int
y):
# type: (...) -> str
# Note that only x has an annotation, y has an implicit Any type
...

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