linting.md

Code formatting and linting

Introduction

Code formatting guidelines set a standard for the layout of your code, for stylistic elements such as use of line breaks and whitespace. Format doesn't have any impact on how the code works, but using a consistent style makes your code more readable, and makes it more likely to be reused.

Linting tools check your code for errors such as a missing bracket or line indent. This can save time and frustration because you can catch errors in advance of running the code.

As a project grows and goes through various stages of development it becomes important to maintain code quality. Using a consistent format and linting your code ensures that it is consistent, readable, and easy to debug and maintain.

Set up Python tools

There are a variety of Python tools available to use with your Kedro projects. This guide shows you how to use ruff.

ruff is a fast linter and formatter that replaces flake8, pylint, pyupgrade, isort, black and more.

• It helps to make your code compliant to PEP 8.
• It reformats code and sorts imports alphabetically and automatically separating them into sections by type.

Install the tools

Install ruff by adding the following lines to your project's requirements.txt file:

ruff # Used for linting, formatting and sorting module imports

To install all the project-specific dependencies, including the linting tools, navigate to the root directory of the project and run:

pip install -r requirements.txt

Alternatively, you can individually install the linting tools using the following shell commands:

pip install ruff

Configure ruff

ruff read configurations from pyproject.toml within your project root. You can enable different rule sets within the [tool.ruff] section. For example, the rule set F is equivalent to Pyflakes.

To start with ruff, we recommend adding this section to enable a few basic rules sets.

[tool.ruff]
select = [
    "F",  # Pyflakes
    "E",  # Pycodestyle
    "W",  # Pycodestyle
    "UP",  # pyupgrade
    "I",  # isort
    "PL", # Pylint
]

It is a good practice to [split your line when it is too long](https://beta.ruff.rs/docs/rules/line-too-long/), so it can be read easily even in a small screen. `ruff` treats this slightly different from `black`, when using together we recommend to disable this rule, i.e. `E501` to avoid conflicts.

Run the tools

Use the following commands to run lint checks:

ruff format --check <project_root>
ruff check <project_root>

You can also have ruff format automatically format your code by omitting the --check flag.

Automated formatting and linting with pre-commit hooks

You can automate the process of formatting and linting with pre-commit hooks. These hooks are run before committing your code to your repositories to automatically point out formatting issues, making code reviews easier and less time-consuming.

Install pre-commit

You can install pre-commit along with other dependencies by including it in the requirements.txt file of your Kedro project by adding the following line:

pre-commit

You can also install pre-commit using the following command:

pip install pre-commit

Add pre-commit configuration file

Create a file named .pre-commit-config.yaml in your Kedro project root directory. You can add entries for the hooks you want to run before each commit. Below is a sample YAML file with entries for ruff:

repos:
  - repo: https://github.com/astral-sh/ruff-pre-commit
    # Ruff version.
    rev: '' # Replace with latest version, for example 'v0.1.8'
    hooks:
      - id: ruff
        args: [--fix]
      - id: ruff-format

See GitHub for the latest configuration for ruff's pre-commit.

Install git hook scripts

Run the following command to complete installation:

pre-commit install

This enables pre-commit hooks to run automatically every time you execute git commit.