As is known, people make mistakes. And always, less or more often… And programming is not an exception. Then, the logical question is how can I protect my code from myself?

The simplest way is a static code analysis. Why? Because of this only requires integration of a tool with a project. Nothing more.

So, what the Python’s world is offering us?

pylint

“Pylint is a tool that checks for errors in Python code, tries to enforce a coding standard and looks for code smells. It can also look for certain type errors, it can recommend suggestions about how particular blocks can be refactored and can offer you details about the code’s complexity.” - https://pylint.readthedocs.io/en/latest/intro.html

The default coding style used by pylint is close to PEP 008.

Installation

pip install pylint

Configuration

Add your .pylintrc configuration file to customize which errors or conventions are important to you. To do that, you could simply run

pylint --generate-rcfile > .pylintrc

Visit a demo project to get an example.

Usage

Simply run a command by using pylint path_to_module_or_package template and you will see:

• all violations you have
• general score for your project like Your code has been rated at 3.96/10

The closer to 10 score is, the better code you have.

For instance, the following command runs checking of the project’s files excluding tests and vevn folders:

pylint $(find . -iname "*.py" -not -path "./tests/*" -not -path "./venv/*")

flake8

“flake8 is a command-line utility for enforcing style consistency across Python projects. By default it includes lint checks provided by the PyFlakes project, PEP-0008 inspired style checks provided by the PyCodeStyle project, and McCabe complexity checking provided by the McCabe project.” - http://flake8.pycqa.org/en/latest/manpage.html

Installation

pip install flake8

Notice! It is very important to install Flake8 on the correct version of Python for your needs. If you want Flake8 to properly parse new language features in Python 3.5 (for example), you need it to be installed on 3.5 for Flake8 to understand those features. In many ways, Flake8 is tied to the version of Python on which it runs.

Configuration

Add your .flake8 configuration file to customize which errors are important to you. To find out more visit http://flake8.pycqa.org/en/latest/user/configuration.html.

Visit a demo project to get an example.

Usage

Simply run a command by using flake8 --statistic path_to_module_or_package and the output will be like

my_pacakge/module1.py:23:25: E126 continuation line over-indented for hanging indent
......
my_pacakge/module12.py:45:26: E126 continuation line over-indented for hanging indent
2     E126 continuation line over-indented for hanging indent
2     E128 continuation line under-indented for visual indent
2     E251 unexpected spaces around keyword / parameter equals
4     E265 block comment should start with '# '
1     F821 undefined name '__class__'

pydocstyle

“pydocstyle is a static analysis tool for checking compliance with Python docstring conventions.” - http://www.pydocstyle.org/en/latest/. It supports most of PEP 257 out of the box.

Installation

pip install pydocstyle

Configuration

Add your .pydocstyle configuration file to customize which options are important to you.

Visit a demo project to get an example.

Usage

Simply run a command like pydocstyle demo_python_at and the output will be like

my_pacakge/module1.py:23 in public method `start`:
        D401: First line should be in imperative mood ('Start', not 'Starts')
my_pacakge/module12.py:33 in public method `stop`:
        D401: First line should be in imperative mood ('Stop', not 'Stops')

Conclusion

These tools will significantly reduce a count of the errors in Python’s code. If you would like to get more insight, just experiment or ask a question in the comments.