Lint

http://www.pylint.org

pip install pylint

• Checking line-code's length,

• Checking if variable names are well-formed according to your coding standard

• Checking if imported modules are used

Usage:

pylint script.py

To decipher warnings and other messages:

• http://pylint-messages.wikidot.com/all-codes

Also it is possible to force pylint to ignore some rule checks:

• In comments in your code before code to ignore:

# pylint: disable=C0321

Create/use pylint config file with all needed settings:

$PYTHON_PATH/lib/site-packages/pylint/standard.rc
pylint --generate-rcfile > standard.rc
disable=W0511, C0321 >> standard.rc
pylint --rcfile=<path>/standard.rc```

Another good linters/checkers are:
* [flake8](https://flake8.pycqa.org) - alternative PEP8 checker
* [ruff](https://github.com/charliermarsh/ruff) - an extremely fast Python linter, written in Rust
* [bandit](https://bandit.readthedocs.io) - security checker
* [mypy](https://mypy.readthedocs.io) - static type checker

## Flake8

> Much better than "default" pylint - the code style is more modern, the comments are more usable

Installation:

```sh
pip install flake8

CLI

Two most useful command examples:

1. Stop the build if there are Python syntax errors or undefined names.

flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics

2. Exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide.

flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics

The arguments can be moved to a config as well.

Config

Flake8 supports storing its configuration in the following places:

Your top-level user directory. In your project in one of setup.cfg, tox.ini, or .flake8. Example:

setup.cfg
  [flake8]
  ignore = E266,E402,E241

or

setup.cfg
  [flake8]
  ignore = D203
  exclude =
    .git,
    __pycache__,
    docs/source/conf.py,
    old,
    build,
    dist
  max-complexity = 10

Error status codes

The symbol associated with a specific check. For example, pycodestyle implements checks that look for whitespace around binary operators and will either return an error code of W503 or W504.

Using Flake8 gives error codes from Flake8 and the lower level PyCode project.

• Flake8 docs

  • Error codes

  • Flake8 errors start with F - F4XX, F5XX, F6XX, F8XX and F901.

• PyCode style

  • Error codes - linked from the Flake8 docs

  • E errors - EXXX.

  • W warnings - WXXX. It looks like these are mostly taken care of by using an IDE to format the code and not using any deprecated code patterns.

    • 100 indentation

    • 200 whitespace

    • 300 blank lines

    • 400 imports

    • 500 line length

    • 600 deprecation

    • 700 statements

    • 900 syntax error

Examples:

F404 	future import(s) name after other statements

E266 	too many leading ‘#’ for block comment
E402 	module level import not at top of file
E241 (*) 	multiple spaces after ‘,’

W606 	‘async’ and ‘await’ are reserved keywords starting with Python 3.7

Ruff

• ⚡️ 10-100x faster than existing linters

• 🐍 Installable via pip

• 🤝 Python 3.11 compatibility

• 📦 Built-in caching, to avoid re-analyzing unchanged files

• 🔧 Autofix support, for automatic error correction (e.g., automatically remove unused imports)

• 📏 Over 500 built-in rules

• ⚖️ Near-parity with the built-in Flake8 rule set

• 🔌 Native re-implementations of dozens of Flake8 plugins, like flake8-bugbear

• ⌨️ First-party editor integrations for VS Code and more

Installation:

pip install ruff

Usage

CLI commands examples:

ruff check .                        # Lint all files in the current directory (and any subdirectories)
ruff check path/to/code/            # Lint all files in `/path/to/code` (and any subdirectories)
ruff check path/to/code/*.py        # Lint all `.py` files in `/path/to/code`
ruff check path/to/code/to/file.py  # Lint `file.py`

Config

Configuration can be done via pyproject.toml, ruff.toml, or .ruff.toml:

[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", "..."]
unfixable = []

VS Code extension

• Extension on VS Visual Studio Marketplace

• GitHub link

Once installed in Visual Studio Code, ruff will automatically execute when you open or edit a Python file.

Interesting commands among others:

• "Fix all": automatically fix all auto-fixable violations

• "Organize Imports": isort-compatible import sorting