Linting¶

Introduction¶

Linting tools are used to improve the quality of your code by checking for errors and making sure it meets a stylistic standard before it is run. As a project grows and goes through various stages of development, it becomes important to maintain the code quality. Linting makes your code more readable, easy to debug and maintain, and stylistically consistent.

Set up linting tools¶

There are a variety of linting tools available to use with your Kedro projects. This guide shows you how to use black, flake8, and isort to lint your Kedro projects.

black is a PEP 8 compliant opinionated Python code formatter. black can check for styling inconsistencies and reformat your files in place. You can read more in the black documentation.
flake8 is a wrapper around pep8, pyflakes, and mccabe which can flag programming errors and coding style inconsistencies with respect to PEP 8, and check the cyclomatic complexity of your code base. You can read more in the flake8 documentation.
isort is a Python library used to sort imports alphabetically and automatically separate them into sections by type. You can read more in the isort documentation.

Install linting tools¶

You can install black, flake8, and isort by adding the following lines to your project’s src/requirements.txt file:

black # Used for formatting code
flake8 # Used for linting code
isort # Used for linting code

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

pip install -r src/requirements.txt

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

pip install black
pip install flake8
pip install isort

Run linting tools¶

Use the following commands to run lint checks:

black --check <project_root>
flake8 <project_root>
isort --profile black --check <project_root>

You can also have black and isort automatically format your code by omitting the --check flag. Since isort and black both format your imports, adding --profile black to the isort run helps avoid potential conflicts.

Automating linting with `pre-commit` hooks¶

You can automate linting by using 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 src/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 black,flake8, and isort:

repos:
  - repo: https://github.com/pycqa/isort
    rev: 5.10.1
    hooks:
      - id: isort
        name: isort (python)
        args: ["--profile", "black"]

  - repo: https://github.com/pycqa/flake8
    rev: ''  # pick a git hash / tag to point to
    hooks:
      - id: flake8

  - repo: https://github.com/psf/black
    rev: 22.8.0
    hooks:
      - id: black
        language_version: python3.9

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.