Mypy: Got 'Need type annotation' error when add type limitation to TypeVar

[yupeng0921]

Below is my code:

  1 #!/usr/bin/env python
  2 
  3 from typing import TypeVar, Generic
  4 
  5 # T = TypeVar('T')
  6 T = TypeVar('T', str, int)
  7 
  8 class MyClass(Generic[T]):
  9 
 10     def __init__(self, value: T)-> None:
 11         self.value = value

When I run mypy against this code, I got below error:
test.py:11: error: Need type annotation for 'value'
But If I change the line 6 to line 5, mypy won't report any error.
Is it a bug or I misunderstand anything?

related packages version:

$ python --version
Python 3.5.2
$ pip freeze
mypy==0.580
typed-ast==1.1.0

[ilevkivskyi]

This is a special case. Here in fact the inferred type for self.value is ambiguous, for example both self.value: T = value and self.value: Union[int, str] = value would work. Therefore mypy asks you what do you actually mean here.

[yupeng0921]

thanks for your explain, the python 3.5 doesn't support variable annotation, so maybe I should just ignore this error.

[ilevkivskyi]

In Python 3.5 you can write self.value = value # type: T mypy treats such comment as an equivalent of a variable annotation.