Python: customize setup actions

Introduction

Sometimes you want to do strange things not planned by software designer, and happily, Python is the best language for introspection. In this post, we are going to extend functionalities of the setup.py file that you may have created to deploy your Python application.

Time to fly!

Let’s create a simple setup.py to start:

from setuptools import setup, find_packages

setup(
    name="test",
    version="1",
    packages=find_packages(),
    author="realitix",
    author_email="mail",
    description="test",
    cmdclass={}
)

Like you can see, I have added a cmdclass property to my setup function. When you type a setup command like python setup.py clean, the distutils module (used by setuptools) will search for the corresponding key in cmdclass property, which is cmdclass['clean'] in our case. The value corresponding to this key must be a class callable by distutils.

If this key doesn’t exist in the cmdclass dictionnary, like install for example, distutils will search through its embedded commands to find the good one.

If you follow me from the start, you should be saying:

OK, I just have to find the command and extend it.

You are right!

Through the path of hidden commands…

Ok I tell you the secret, to find theses commands, just find distutils path:

python -c "import distutils; import os; print(os.path.dirname(distutils.__file__))"

Then go in <distutils_path>/commands and there you are.

Let’s get back to the point

Now that you understand how it works, we can easily extend the setup commands. Let’s extend the clean command.

from distutils.command.clean import clean
from setuptools import setup, find_packages


class MyClean(clean):
    def run(self):
        # Execute the classic clean command
        super().run()

        # Just add a print for the example
        print("exemple")

setup(
    name="test",
    version="1",
    packages=find_packages(),
    author="realitix",
    author_email="mail",
    description="test",
    cmdclass={'clean': MyClean}
)

And… it works like a charm!

To go further

Do you enjoy the integrated distutils command ? Yes for sure ! But what if you could create your custom command ? It’s not a surprise but yes you can do it !

from distutils.cmd import Command

class MyCommand(Command):
    description = "Description of the command"
    user_options = []

    # This method must be implemented
    def initialize_options(self):
        pass

    # This method must be implemented
    def finalize_options(self):
        pass

    def run(self):
        print("My command runs!")