flake8-kotoha

KoToHa: Kaizen Type Hint

Install

uvx (Recommended)

The easiest way to run flake8 (without manually installation).

$ uvx --with flake8-kotoha flake8 .

Other options

pipx

$ pipx install --preinstall flake8-kotoha flake8
$ flake8 -h
...
Installed plugins: flake8-kotoha: 0.1.0, ...

venv + pip

$ python -m venv .venv --upgrade-deps
$ .venv/bin/python -m pip install flake8-kotoha
$ .venv/bin/flake8 -h
...
Installed plugins: flake8-kotoha: 0.1.0, ...

uv

$ uv tool install flake8 --with flake8-kotoha
$ flake8 -h
...
Installed plugins: flake8-kotoha: 0.1.0, ...

Usage

def plus_one(numbers: list[int]) -> list[int]:
    return [n + 1 for n in numbers]

$ flake8 example.py
example.py:1:14: KTH101 Type hint with abstract type `collections.abc.Iterable` or `collections.abc.Sequence`, instead of concrete type `list`

Error codes

Type hints in function parameters

Use abstract types instead of concrete ones

Rationale

https://docs.python.org/ja/3/library/typing.html#typing.List

Note that to annotate arguments, it is preferred to use an abstract collection type such as Sequence or Iterable rather than to use list or typing.List.

https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html#standard-duck-types

Use Iterable for generic iterables (anything usable in "for"), and Sequence where a sequence (supporting "len" and "__getitem__") is required

https://typing.readthedocs.io/en/latest/reference/best_practices.html#arguments-and-return-types

For arguments, prefer protocols and abstract types (Mapping, Sequence, Iterable, etc.).