/ #packaging #tox 

2 Critical Python packaging tools

At last week’s Python Frederick meetup, I gave a talk on Python packaging. My aim was to cover how packaging works and how to build a basic package. Over the course of the talk, we used a couple of tools that I think are critical for releasing a Python package to PyPI. I’ll describe these tools and why I think they are critical.


tox is a fantastic tool for testing packaging. With the tox command, a developer can build a package, install it into a virtual environment for a specific Python version, and run the package through its test suite.

The short version of running tox looks like:

$ tox -e py36

This command will run a package’s test suite against Python 3.6. I love it when commands are that elegant. To make that possible, the developer must tell tox how to run the test suite. This configuration is done in a tox.ini file. A minimal file could look like:

envlist = py36

commands = python -m unittest discover \
    -s {envsitepackagesdir}/whirlygig

In this example, you would change whirlygig to the name of your project. This is enough information to inform tox about how to run your test suite.

I find that using tox saves me from hard to catch packaging bugs (did you know those exist?) and is generally awesome for testing against multiple versions of Python.


twine is a critical tool in a packager’s toolbelt for one reason: it let’s you upload to PyPI over HTTPS. In contrast, python setup.py upload uses insecure HTTP for many versions of Python.

Even though it seems silly, you need a separate package to upload securely over HTTPS. I presume there are good reasons for that requirement that I’m unaware of.

python setup.py sdist bdist_wheel creates a dist directory with the packages to upload. You can perform your upload with:

$ twine upload dist/*


The Python ecosystem has excellent documentation about packaging at the Python Packaging User Guide. This post was meant to be a gentle introduction to a couple of very valuable tools when you want to work with packages.

(Yes, I know a “package” is technically called a “distribution” in proper Python lingo, but I used the term as it is more broadly accepted among many programming languages.)


Matt Layman

Matt Layman is a software engineer from Frederick, MD. He is an open source software maintainer and advocate for the Python programming language.

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