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Boost Your Python Code Quality with PyLint: Top Tips and Tricks

Introduction

Here, I will discuss what exactly is PyLint?, and when to use PyLint. I will also provide some tips and tricks to enhance the code quality.

Code Quality

Code quality encompasses readability, maintainability, efficiency, and reliability in software development. Well-written, organized code is easy to understand, modify, and scale. High code quality reduces bugs, speeds up development, and enhances overall software performance, ensuring reliability, maintainability, and user satisfaction through robust, error-free solutions.

A Quality code should have the following

  • It does not do what it is supposed to do
  • It does contain defects and problems
  • It is difficult to read, maintain, or extend

PEP8

PEP 8 is the official style guide for Python code, outlining conventions for formatting, naming, and organizing code to enhance readability and consistency. It promotes best practices such as using consistent indentation, naming conventions, and spacing. Adhering to PEP 8 ensures clean, maintainable, and Pythonic code. For a detailed guide, visit the: PEP8 Style Guide

PyLint

Python PyLint is a static code analysis tool that evaluates Python code for errors, style issues, and potential vulnerabilities. It enforces coding standards, identifies common programming mistakes, and promotes best practices. PyLint enhances code quality, readability, and maintainability by providing automated feedback and suggestions for improvement.

To install PyLint, you can use Python's package manager, pip. Open your command-line interface and run the following command:

python -m pip install pylint //or python3

This command will download and install the latest version of PyLint from the Python Package Index (PyPI) along with any dependencies it requires.

Features of Python PyLint

  • Static Code Analysis: PyLint performs static analysis of Python code to identify errors, potential bugs, and style violations.
  • Coding Standard Enforcement: It enforces adherence to coding standards such as PEP 8, enhancing code consistency.
  • Customizable Rules: Users can customize PyLint's ruleset to fit project-specific requirements.
  • Integration with IDEs: PyLint seamlessly integrates with popular integrated development environments (IDEs) like VS Code and PyCharm.
  • Automated Feedback: It provides automated feedback on code quality issues, helping developers improve their coding practices.
  • Continuous Integration Support: PyLint can be integrated into continuous integration pipelines to enforce code quality standards.
  • Extensibility: Developers can extend PyLint's functionality through plugins to address specific project needs.

Drawbacks of Python PyLint

While PyLint offers comprehensive code analysis capabilities, it does have some limitations. One drawback is its potential to generate false positives, flagging code constructs that are not necessarily errors or issues. This can sometimes lead to frustration for developers, who may spend time investigating and addressing non-existent problems. Additionally, configuring PyLint's ruleset to align with project-specific requirements can be time-consuming and complex, especially for larger codebases. Despite these drawbacks, PyLint remains a valuable tool for improving Python code quality when used judiciously and in conjunction with other quality assurance practices.

PyLint checks for

  • Basic errors like syntax errors
  • Class nodes
  • Potential misdesign
  • Exceptions
  • Formatting issues
  • Import statements
  • Logging module
  • Code which can be refactored
  • Encoding issues
  • Similar or duplicate code
  • Spelling in comments and docstrings
  • String literals
  • Bugs in the code using type inference
  • Variables

To get a list of all checks, please visit PyLint features

Using PyLint

Once you are done installing PyLint into your environment, you need to run the following command to allow PyLint to analyze your code

python -m pylint <filename>.py

Here in the above command, you can specify a list of Python files or you can use the following command to parse all the files from a specific directory.

python -m pylint <directoryname>

if you wish to parse more than 1 directory, you can do so by specifying one after another in the same command.

How to run process multiple files in parallel with PyLint?

To parse multiple files in parallel use "-j" followed by the number of threads or pylint subprocesses you want to run

python -m pylint -j 4 mymodule1.py mymodule2.py mymodule3.py mymodule4.py

Four parallel PyLint subprocesses are spawned to check each provided module simultaneously. Detected issues by checkers are not displayed instantly but are shown after the completion of checking a module.

PyLint Message Type

  • [I]nformational messages that Pylint emits (do not contribute to your analysis score)
  • [R]efactor for a "good practice" metric violation
  • [C]onvention for coding standard violation
  • [W]arning for stylistic problems, or minor programming issues
  • [E]rror for important programming issues (i.e. most probably a bug)
  • [F]atal for errors which prevented further processing

Manipulating PyLint Output Format

PyLint output can be formatted as we like. For example, consider a case where we want to save the output to a JSON file, for that we can use the following

--output-format=json:somefile.json,colorized
  • By default, output goes to stdout; redirect it to a file with `--output=<filename>`.
  • Change the output format with `--output-format=<value>`: options include text, JSON, parseable, colorized, and msvs (for Visual Studio).
  • Combine multiple formats using comma separation and redirect to a file using a colon.

Custom message format

You can customize the exact way information is displayed using the --msg-template=<format string> option. For example:

pylint --msg-template='{msg_id}:{line:3d},{column}: {obj}: {msg}'

Following is a list of all possible custom message formats

abspath Absolute Path to the File
line Line Number
column Column Number
end line Line Number of the End of the Node
end column Column Number of the End of the Node
module Module Name
object Object Within the Module (if any)
message Text of the Message
message ID The Message Code (e.g., I0011)
symbol Symbolic Name of the Message (e.g., locally-disabled)
c One-letter indication of the Message Category
category Full Name of the Message Category


How to disable certain errors to be detected by PyLint

Many times, as a developer we have to write code, which does not follow PEP8. In that case, we need to forcefully bypass those checks.

1. To bypass all violations on a single line

a, b = ... # pylint: disable=unbalanced-tuple-unpacking

2. To bypass all violations of the following line

# pylint: disable-next=unbalanced-tuple-unpacking
a, b = ...

3. To bypass all violations in a single scope

def test():
    # Disable all the no-member violations in this function
    # pylint: disable=no-member
    ...

4. To bypass all violations in a block.

def meth5(self):
    # pylint: disable=no-member
    # no error
    print(self.bla)
    if self.blop:
        # pylint: enable=no-member
        # enable all no-members for this block
        print(self.blip)
    else:
        # This is affected by the scope disable
        print(self.blip)
    # pylint: enable=no-member
    print(self.blip)
    if self.blop:
        # pylint: disable=no-member
        # disable all no-members for this block
        print(self.blip)
    else:
        # This emits a violation
        print(self.blip)

Note. As PyLint improves and reduces false positives, accumulated disables that have become unnecessary can clutter the code. To address this, you can enable the "useless-suppression" warning, which helps identify and remove such unnecessary disables, streamlining the codebase.

Conclusion

Harnessing the power of PyLint can significantly elevate the quality of your Python code. By implementing the top tips and tricks outlined in this article, developers can streamline their workflow, reduce errors, and enhance overall code maintainability. Embracing PyLint is not just about improving code quality; it's about fostering a culture of excellence and efficiency in software development. Take these insights, apply them to your projects, and watch as your Python code reaches new heights of clarity, reliability, and effectiveness.


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