Pre-commit hooks are scripts that run automatically before a commit is made. In my post Adding pre-commit Hooks to Python Repo, I explained how to configure pre-commit hooks in your repo and address the issues identified by them.
After understanding how to setup these hooks, the next question is what hooks should I use and why? Here are five common reasons to use pre-commit hooks for Python and some example plugins that you can use for each reason.
Check for Syntax Errors
If your code contains syntax errors, it will not be able to run. It is important to fix all syntax errors before you try to run your program. Syntax errors can be caused by a variety of things, such as missing parentheses or mismatched indentation. Checking your code for syntax errors can help you identify and fix mistakes that could otherwise cause your program to behave unexpectedly or to crash.
A pre-commit hook can check your Python code for syntax errors, ensuring that the code you’re committing will run properly. Pylint is a comprehensive linter that checks your code for a wide range of issues, including syntax errors, style violations, and semantic problems. It can be configured to run as a pre-commit hook.
Enforce Code Formatting Standards
Enforcing code formatting standards can help to ensure that your code is easy to read and understand, which can make it easier for other developers to work with your code and contribute to your project. It can also help to prevent certain types of errors and make it easier to identify and fix other types of errors.
In addition, having consistent formatting across your codebase can make it easier to identify differences between versions of your code when using version control systems such as Git. This can be especially useful when working on a team, as it can help to ensure that everyone is following the same coding standards.
Overall, enforcing code formatting standards can help to improve the quality, readability, and maintainability of your code, which can save time and reduce frustration for you and other developers working on your project.
You can use a pre-commit hook to enforce a particular code formatting style, such as PEP 8, by running a linter like flake8 or black.
Check For Test Coverage
Checking for test coverage can help you to identify areas of your code that are not being tested by your unit tests. This can be important for a few reasons:
- It can help you to ensure that your code is working correctly and is free of errors. By writing unit tests that cover a wide range of scenarios and edge cases, you can increase your confidence that your code is functioning as intended.
- It can help you to identify areas of your code that may be at risk of breaking if you make changes. If you make changes to a part of your code that is not covered by unit tests, you may not realize that you have introduced an error until you try to run the code.
- It can help you to identify areas of your code that are hard to test. If you find that you are having difficulty writing unit tests for a particular part of your code, this may be an indication that the code is overly complex or difficult to understand.
Overall, checking for test coverage can help you to improve the quality and reliability of your code, and can save you time and frustration in the long run
A pre-commit hook such as pytest can run your unit tests and check that they have sufficient coverage, ensuring that your code is tested before it is committed.
Check For Security Issues
Checking your code for security issues is important because it can help protect your application and its users from malicious attacks. Some common types of security vulnerabilities include SQL injection, cross-site scripting (XSS), and cross-site request forgery (CSRF). If an attacker is able to exploit one of these vulnerabilities in your application, they could potentially gain access to sensitive data, compromise the security of your application, or even take control of your entire system. By proactively identifying and fixing security issues in your code, you can help prevent these types of attacks and ensure that your application is secure.
A tool like Bandit can be used in pre-commit hooks to check your code for common security vulnerabilities.
Run Type Checking
There are several reasons why you should run type checking in your Python code:
- Improved reliability: Type checking helps ensure that your code is using the correct types of data and variables. This helps reduce the likelihood of errors or bugs in your code.
- Easier debugging: When you run type checking, you can more easily identify any type-related issues in your code. This makes debugging your code easier and more efficient.
- Enhanced readability: Type checking helps make your code more readable and easier to understand. This is especially important if you are working on a team or if you plan to share your code with others.
- Enhanced performance: Type checking can also help improve the performance of your code. For example, if you are using a list or other data structure that is not optimal for the task you are trying to accomplish, type checking can help you identify this issue and correct it.
Overall, running type checking in your Python code can help improve the reliability, readability, and performance of your code.
A pre-commit hook can run a static type checker like mypy to ensure that your code adheres to your type hints and to catch type-related errors before they make it into your codebase.