Using mypy's generic self with python2 type comments

Question

I have a case where I would like to use a generic self for typing with mypy. However I need to maintain python 2.7 compatibility, so I'm using the type comment syntax.

from typing import TypeVar

T = TypeVar('T', bound='Shape')

class Shape:
    def set_scale(self: T, scale: float) -> T:
        self.scale = scale
        return self

How do I translate this code to a type comment? Type comments omit the 'self' type, so the T definition gets lost:

    def set_scale(self, scale):
        # type: (float) -> T

Answer 1

You don't have to exclude self ; you simply have the option to do so:

When using the short form (eg # type: (str, int) -> None) every argument must be accounted for, except the first argument of instance and class methods ( those are usually omitted, but it's allowed to include them ).

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From PEP-484, third note at the end of Suggested Syntax for Python 2.7 and straddling code

So you can write

def set_scale(self, scale):
    # type: (T, float) -> T

It's the job of the consumer of such a comment to count parameters and determine if self was omitted or not.