flake8-typing-only-imports

Plugin is still a work in progress

Tells you which imports to put inside type-checking blocks.

Codes

Rationale

TYO100 guards against import cycles . TYO101 applies the same logic, for venv or stdlib imports.

Remaining error codes are there to help manage forward references, either by telling your to use string literals where needed, or by enabling postponed evaluation of annotations. The error code series TYO2XX and TYO3XX should therefore be considered mutually exclusive, as they represent two different ways of managing forward references.

See this excellent stackoverflow answer for a quick explanation of forward references.

Installation

pip install flake8-typing-only-imports

Suggested use

Only enable TYO101 if you're after micro performance gains on start-up.

TYO2XX and TYO3XX are reserved for error codes to help manage forward references. It does not make sense to enable both series, and they should be considered mutually exclusive.

If you're adding this to your project, we would recommend something like this:

select = TYO100, TYO200, TYO200  # or TYO300 and TYO301

ignore = TYO101, TYO300, TYO301  # or TYO200 and TYO201

Examples

Bad code

models/a.py

from models.b import B

class A(Model):
    def foo(self, b: B): ...

models/b.py

from models.a import A

class B(Model):
    def bar(self, a: A): ...

Which will first result in these errors

>> a.py: TYO101: Move third-party import 'models.b.B' into a type-checking block
>> b.py: TYO101: Move third-party import 'models.a.A' into a type-checking block

and consequently trigger these errors if imports are purely moved into type-checking block, without proper forward reference handling

>> a.py: TYO300: Annotation 'B' needs to be made into a string literal
>> b.py: TYO300: Annotation 'A' needs to be made into a string literal

Good code

models/a.py

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from models.b import B

class A(Model):
    def foo(self, b: 'B'): ...

models/b.py

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from models.a import A

class B(Model):
    def bar(self, a: 'A'): ...

As a pre-commit hook

You can run this flake8 plugin as a pre-commit hook:

- repo: https://gitlab.com/pycqa/flake8
  rev: 3.7.8
  hooks:
    - id: flake8
      additional_dependencies: [ flake8-typing-only-imports ]

Supporting the project

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Contributions are always welcome 👏