pyflakes: Undefined name error for unimported type hints written as string

PEP484 explicitly allows unimported types to be specified as a string. pyflakes 2.0.0 tries to parse these strings and is unable to find the correct typedefs and reports an unexpected error.

def hello(a: "Unknown") -> str:
    return str(a)

generates the pyflakes error

foo.py:1: undefined name 'Unknown'

About this issue

Original URL
State: closed
Created 6 years ago
Reactions: 9
Comments: 16 (11 by maintainers)

Commits related to this issue

non-typing annotations are no longer officially supported see: https://github.com/PyCQA/pyflakes/issues/340#issuecomment-536770053 — committed to openkinome/kinoml by jaimergp 4 years ago
Remove type annotation that gives issues with flake8 (https://github.com/PyCQA/pyflakes/issues/340) — committed to ESMValGroup/ESMValTool by stefsmeets 4 years ago

Most upvoted comments

Annotations do not have to be used for type hints though. They were introduced in PEP 3107.

These annotation consumers can do anything they want with a function’s annotations. For example, one library might use string-based annotations to provide improved help messages, like so:

Pyflakes should not require them to be type hints.

PetterS on Dec 30, 2018

is anything done to fix this?

I currently use typing however cannot import the annotated type as it will give a circular import creating a whole new range of bugs. That might be a symbol of some bad software design on my end (not sure) but it’s problematic to add NOQA to multiple function definitions in my django application

C0DK on Jul 15, 2019

what about the usual “import for type annotations” approach:

if False:  # if typing.TYPE_CHECKING if you don't care about 3.5.0 / 3.5.1
    import accounts.models

def get_upcoming_deposits(self, user: "accounts.models.User"): ...

asottile on Jul 22, 2019

Can you use the mypy only import?

if False:  # or typing.TYPE_CHECKING  if python3.5.3+
    from ...

Though circular imports are often an indication of a design problem

asottile on Jul 15, 2019