Skip to content

None inferred as variable type from UninhabitedType #4104

Closed
Closed
None inferred as variable type from UninhabitedType#4104
Labels
bugmypy got something wrongpriority-1-normaltopic-type-variables

Description

@JukkaL
JukkaL
opened on Oct 12, 2017

The inferred type for x is unexpected (especially when using --strict-optional):

from typing import TypeVar

T = TypeVar('T')

def f() -> T: pass

x = f()
reveal_type(x)  # None

It would be better to require an annotation for x.

Activity

  1. JukkaL
    added
    bugmypy got something wrong
    priority-1-normal
    topic-type-variables
    on Oct 12, 2017

  2. gvanrossum commented on Oct 12, 2017

    @gvanrossum
    gvanrossum
    on Oct 12, 2017
    Member

    Why is the definition of f() not considered an error?

  3. ilevkivskyi commented on Oct 13, 2017

    @ilevkivskyi
    ilevkivskyi
    on Oct 13, 2017
    Member

    @gvanrossum

    Why is the definition of f() not considered an error?

    Because it is not unsafe. As discussed in #2885 we can't prohibit all possible useless annotations. Moreover now we have #4066, so that I think the way forward is to prohibit empty bodies (so that one can't make a body for such annotations).

  4. gvanrossum commented on Oct 13, 2017

    @gvanrossum
    gvanrossum
    on Oct 13, 2017
    Member

    It may not be unsafe, but I'm pretty sure that whenever you see that, the user misunderstands what type variables are on a fundamental level (e.g. they confuse them with type aliases).

  5. JukkaL
    closed this as completedin #4112on Oct 13, 2017
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

No one assigned

    Labels

    bugmypy got something wrongpriority-1-normaltopic-type-variables

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions