Artalus / pre-commit-mypy

Wrapper for my.py to be used in pre-commit hooks

Wrapper for mypy type checker to be used in pre-commit. Supposed to be a proper workaround not needing --ignore-missing-imports - at the cost of an additional config file.

How to use

Add the hook to your .pre-commit-config.yaml:

repos:
- repo: https://github.com/Artalus/pre-commit-mypy
  rev: v0.1
  hooks:
  - id: mypy

Create file .pre-commit-mypy.yaml, specifying paths to the mypy executable you want to use, or python executable you want it to work with through --python-executable flag:

# .pre-commit-mypy.yaml
mypy: D:\git\pre-commit-mypy\test\venv\Scripts\mypy.exe
# you can specify either one of these paths, and even both
python: D:\git\pre-commit-mypy\test\venv\Scripts\python.exe

On Windows, the path will be something like d:/git/myproject/venv/Scripts/mypy.exe. On Linux - /home/user/git/myproject/venv/bin/mypy

Finally, add .pre-commit-mypy.yaml to your .gitignore - the path is local to your machine, and will differ for your colleagues and CI machines.

Done. Now pre-commit install, break something, and try to commit it:

$ pre-commit run --all-files
mypy.....................................................................Failed
- hook id: mypy
- exit code: 1

PCMW :  Will run:
PCMW :  Command: ['D:\\git\\pre-commit-mypy\\test\\venv\\Scripts\\mypy.exe', 'test.py']
PCMW :  CWD: D:\git\pre-commit-mypy\test


test.py:11: error: Incompatible return value type (got "int", expected "Result[int, MyError]")  [return-value]
Found 1 error in 1 file (checked 1 source file)

mypy: or python: ?

mypy path provided in config has more priority than python.

• If you specify only mypy, then the hook will essentially run simply path/to/mypy.exe changed_file.py.
• If you specify only python, the hook will resolve to path/to/python.exe -m mypy changed_file.py.
• If you specify both, the hook will use python path as an argument for mypy: path/to/mypy.exe --python-executable path/to/python.exe changed_file.py. This might be beneficial if you have weird setup where mypy executable is set up separately from the environment you use it with.

Why use this?

Using pre-commit + mypy + VS Code (and probably any other IDE as well) has 2 quirks:

1. pre-commit tends to install its hooks in a separate virtualenv. Thus, mypy installed from the official mirrors-mypy hook repo will not know anything about packages and their types used in your project's environment. You need the hook to either launch your venv-specific mypy executable, or to specify path to your python in your venv via --python-executable parameter. Neither of these workarounds are really portable between OSes and developers.

2. VS Code specifically runs git commands without any notion of virtualenvs at all. So even if you use repo: local, entry: mypy hook in your .pre-commit-config.yaml as a workaround, pre-commit launched from Code will not know where this mypy comes from in an arbitrary case.

The wrapper will read a user-provided path to their local mypy from a git-ignored config file and will use it to check the files indicated by pre-commit executable. If no config is provided, the wrapper will fallback to mypy executable present in PATH, if any.