flake8-kotoha

KoToHa: Kaizen Type Hint

Install

pipx

$ pipx install flake8
$ pipx inject flake8 flake8-kotoha
$ 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

error code	description
KTH101	Use Iterable or Sequence instead of list
KTH102	Use Iterable or Sequence instead of tuple
KTH103	Use Iterable instead of set
KTH104	Use Iterable instead of dict

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.).