1.
Thomas Aglassinger
https://roskakori.at
Helpful pre-commit
hooks for Python and
Django

2.
What is pre-commit?
●
A framework to manage git pre-commit hooks.
●
To perform quality check on code before accepting a
commit.
●
Many handy hooks available through it.
●
Helps you catch many (often minor issues) before they make
it into the repository.

3.
How to get pre-commit
●
Visit https://pre-commit.com/
●
Various methods to install:
– Plain Python: pip install pre-commit
– Anaconda: conda install -c conda-forge pre-commit
– Ubuntu: sudo apt-get install pre-commit
– MacOS: brew install pre-commit

4.
Configuration
●
Add a file “.pre-commit-config”
●
Add the github repositories and hooks you want to run before each commit.
●
Example:
●
Run “pre-commit install”
●
Hooks are checked on
“git commit ...” and commit in IDE
●
Manually run hooks using
“pre-commit run --all-files”
exclude: "^.idea"
repos:
- repo: git://github.com/pre-commit/pre-commit-hooks
rev: v3.2.0
hooks:
- id: trailing-whitespace
- id: end-of-file-fixer
- id: mixed-line-ending
args: ["--fix=auto"]

5.
Configuration
●
Add a file “.pre-commit-config”
●
Add the github repositories and hooks you want to run
before each commit.
●
Example: exclude: "^.idea"
repos:
- repo: git://github.com/pre-commit/pre-commit-hooks
rev: v3.2.0
hooks:
- id: trailing-whitespace
- id: end-of-file-fixer
- id: mixed-line-ending
args: ["--fix=auto"]
Regex for files and
folders not to check
Source code repository
and version of hooks
to use
Hooks to use
Parameters for a
specific hook

6.
Standard hooks – Text files
●
- repo: git://github.com/pre-commit/pre-commit-hooks
rev: v3.2.0
●
trailing-whitespace: remove white space at end of line in
text files
●
mixed-line-ending: detect or fix mixed line endings (e.g
developers on Windows and Unix working on same code)
●
end-of-file-fixer: Ensures that text files end with a newline
character.

7.
Example hooks

8.
Standard hooks – Unwanted files
●
check-byte-order-marker: rejects text files starting with
UTF-8 BOM (as created by various Microsoft tools like
Notepad, causing many Unix tools to fail)
●
check-added-large-files: rejects large files; possibly specify
what is large: args: ["--maxkb=768"]
●
Check-merge-conflict: refuse to commit before all merge
conflicts are resolved

9.
Standard hooks - Python
●
check-ast: check Python syntax
●
requirements-txt-fixer: sorts entries in requirements.txt
●
debug-statements: refuse to commit calls to breakpoints()
and imports of debugger

10.
Standard hooks – Syntax checks
●
check-json
●
check-toml
●
check-xml
●
check-yaml

11.
Pretty print Python
●
Using black (opinionated): https://github.com/psf/black
●
Configure using pyproject.toml
- repo: https://github.com/ambv/black
rev: stable
hooks:
- id: black
[tool.black]
line-length = 120
include = '.pyi?$'
exclude = '''
/(
.eggs
| .git
| venv
| build
| dist
)/
'''

12.
Sort imports consistently
●
Using isort:
https://github.com/timothycrosley/isort
●
Configure using setup.cfg
●
Can be tricky to work with black
→ see example to the right
- repo: https://github.com/timothycrosley/isort
rev: 5.4.2
hooks:
- id: isort
[tool:isort]
# Use project line length.
line_length = 120
# Packages from own projetc
default_section = THIRDPARTY
known_first_party = mytool, niftysite
# Use same style as black.
force_grid_wrap=0
include_trailing_comma = True
multi_line_output=3
use_parentheses=True
# Skip virtual environments.
skip_glob = venv

13.
Flake8 – Semantic Python check
●
Find unused imports, shadowed variables, string formatting,
unreachable code, …
●
Configure using setup.cfg
- repo: https://gitlab.com/pycqa/flake8
rev: 3.8.3
hooks:
- id: flake8
[flake8]
max-line-length = 120
ignore = E203, W503
exclude =
.git
build
dist
venv
docs/conf.py

14.
Prettier – Pretty print various formats
for web development
●
Supports JavaScript, CSS, Markdown, HTML, GraphQL, YAML
and others by means of plugins
●
Does not work with Django HTML templates → exclude using
“.prettierignore” (uses same format as .gitignore)
- repo: https://github.com/prettier/prettier
rev: 2.0.5
hooks:
- id: prettier
**/coverage.xml
**/templates/**/*.html

15.
Summary
●
Pre-commit is easy to install and configure.
●
Solves minor minor issues arising when multiple developers
work on the same code.
●
Plenty of available hooks.