Setting Up Automatic Linting and Type Checking (Python, GHA)

CI/CD
,

I work with open-source & private Python projects on GitHub on a daily basis.
I use Github Actions to run my tests, linting, static type checking, and other CI/CD tasks.

In this short guide I wanted to share my go-to tools and configurations for setting up my projects.
Here, I will mostly focus on setting up linting with ruff and static type checking with mypy.

The main goal is to be able to run both ruff and mypy on every pull request, and every push to the main branch.
Additionally we would want to be able to run these tools locally, with the same configuration so that we get consistent results locally & remote.

Step 1 - Install dependencies

I personally love using pipenv, so in that case create/open a Pipfile in the root of your project and copy the following contents:

1
2
3
4
5
6
7
8
[[source]]
url = "https://pypi.python.org/simple"
verify_ssl = true
name = "pypi"

[dev-packages]
ruff = "*"
mypy = "*"

This basically specifies that our project has two dev dependencies of latest ruff & mypy.

In order to install these dependencies, simply run pipenv install --dev.

Step 2 - Configure the tools

As one of our goals was to have consistent results between remote & local executions, I like having a configuration file for all of the tools, which means I like having a pyproject.toml.

Create/open your pyproject.toml file in the root of your project and copy the following contents:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
[tool.mypy]
strict = true

[tool.ruff]
# Enable pycodestyle (`E`) and Pyflakes (`F`) codes by default.
select = ["E", "F"]
ignore = []

# Allow autofix for all enabled rules (when `--fix`) is provided.
fixable = ["A", "B", "C", "D", "E", "F", "G", "I", "N", "Q", "S", "T", "W", "ANN", "ARG", "BLE", "COM", "DJ", "DTZ", "EM", "ERA", "EXE", "FBT", "ICN", "INP", "ISC", "NPY", "PD", "PGH", "PIE", "PL", "PT", "PTH", "PYI", "RET", "RSE", "RUF", "SIM", "SLF", "TCH", "TID", "TRY", "UP", "YTT"]
unfixable = []

# Exclude a variety of commonly ignored directories.
exclude = [
    ".bzr",
    ".direnv",
    ".eggs",
    ".git",
    ".hg",
    ".mypy_cache",
    ".nox",
    ".pants.d",
    ".pytype",
    ".ruff_cache",
    ".svn",
    ".tox",
    ".venv",
    "__pypackages__",
    "_build",
    "buck-out",
    "build",
    "dist",
    "node_modules",
    "venv"]

line-length = 120

To read more about the configurations options, refer to the respective docs:

Step 3 - Setting up a remote workflow with GHA

After step 2, you should be able to run both ruff & mypy locally.
Now you will set an automatic workflow on GitHub, which will run ruff & mypy whenever a PR is opened and/or there was a push to the main branch.

Create a file linting_and_type_check.yaml under .github/workflows and copy the following contents:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
name: lint_and_type_check
on:
  push:
    branches:
      - main
  pull_request:
jobs:
  ruff:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: chartboost/ruff-action@v1

  mypy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2

      - name: Set up Python
        uses: actions/setup-python@v2
        with:
          python-version: 3.8

      - name: Install pipenv
        run: pip install pipenv

      - name: Install dependencies
        run: pipenv install --dev

      - name: Run mypy
        run: pipenv run mypy .

If the above syntax is a bit mysterious, you can go through the syntax docs.

As soon as you will push the above file, you will see the actions being triggered.
Verify that both ruff and mypy executed successfully, and that they have consistent results with your local executions.

On GitHub, it should look like the following

Feel free to tweak this process with your own favorite tools, and if you have any questions you can reach out to me on twitter.