A story about trying to introduce Linter in the middle of a Python (Flask) project

topic

--The backend (Flask) code of the project you are participating in has had a hard time (still ongoing) because Linter and formatter have not been introduced.

Hope

――Do you want to lint & format with Githook? ?? ?? ?? ?? ??

problem

--The code written at the beginning of the project ignores pep8 gun and introduces lint, an error occurs. ――I want to apply autofix at once, but the difference is too large to review. ――I want to refactor the whole amount, but there is no man-hours, and the test code does not seem to be enough

compromise

--Lint & format is applied to the newly created code. --The existing code remains as it is --Review the test code of the existing code and implement it additionally so that it can be refactored at any time. --Lint is applied with hook. The format is decided by the human being (a measure of bitterness). --Existing is forced to commit with git commit --no-verify

Development method

If new

1. Coding
2. Lint runs at commit
3. Apply formater black hogehoge.py
4. If you have to fix it by hand, fix it until the error disappears and commit (lintflake8 hogehoge.py by specifying the file)
5. Push to pull request review

If you want to get existing code

1. Coding
2. Lint runs at commit
3. If there is an error, check the error in the additional part with black hogehoge.py --diff and fix it by hand. (Lintflake8 hogehoge.py by file specification)
4. When committing, skip the hook with git commit --no-verify
5. Push to pull request review

Linter settings

linter uses flake8.

1. pip install flake8
2. Create a configuration file (create .flake8 in the project root)

.flake8

[flake8]
ignore = E203, E266, E501, W503, F403, F401
max-line-length = 79
max-complexity = 18
select = B,C,E,F,W,T4,B9

* Change the flake8 settings as appropriate.

--Honestly, max-line-length <80 is too few in modern times ――E203, W503, W504 are required for igonore because of the relationship with black. Other than that, as appropriate -Look here

formatter settings

formatter uses black

1. pip install black
2. Create a configuration file (create pyproject.toml in the project root)

pyproject.toml

[tool.black]
line-length = 79
include = '\.pyi?$'
exclude = '''
/(
    \.git
)
'''

Match with flake8

――I'm surprised when I sometimes get an error even though I use formatr.

githook settings

Use pre-commit to set the hook.

1. pip install pre-commit
2. Create configuration file (install .pre-commit-config.yaml in the project root)

repos:
- repo: https://github.com/pre-commit/pre-commit-hooks
rev: v2.4.0
hooks:
- id: flake8

Summary

――Because of the introduction period of the tool, manual work is included. Change little by little --Lint and formater should be entered first. The minimum rules (pep8) should be included ――Change the rules when you find it difficult to write --If the test code is correct, there is no problem with the existing ones.