flake8-typing-only-imports

flake8 plugin which flags imports which are exclusively used for type hinting.

Installation

pip install flake8-typing-only-imports

Codes

Rationale

A common trade-off for annotating large code bases is you will end up with a large number of extra imports. In some cases, this can lead to import circularity problems.

One (good) solution, as proposed in PEP484 is to use forward references and type checking blocks, like this:

from typing import TYPE_CHECKING


if TYPE_CHECKING:
    from app.models import foo


def bar() -> 'foo':
    ...

At the same time, this is often easier said than done, because in larger code bases you can be dealing with hundreds of lines of imports for thousands of lines of code.

This plugin eliminates that problem by flagging imports which can be put inside a type-checking block.

As a pre-commit hook

See pre-commit for instructions

Sample .pre-commit-config.yaml:

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

Release process

1. Bump version in setup.cfg.
2. Add a commit "Release vX.Y.Z".
3. Make sure checks still pass.
4. Draft a new release with a tag name "X.Y.Z" and describe changes which involved in the release.
5. Publish the release.

Flake8 Type Hinting Only Imports

This is flake8 hook flags all your imports that are being exclusively used for type hinting.

Running the hook on

import a

from b import c


def example(d: c):
    return a.transform(d)

Will produce this

> ../file.py:3:1: TYO100: Import 'c' only used for type annotation

Motivation

• Circular imports
• Efficiency
• How are imports handled at compile time
• More type hinting -> exaggerated problem