This lesson is being piloted (Beta version)

Packaging Code for Release


Teaching: 0 min
Exercises: 90 min
  • How do we prepare our code for sharing as a Python package?

  • How do we release our project for other people to install?

  • Describe the steps necessary for sharing Python code as installable packages.

  • Use Poetry to prepare an installable package.

  • Explain the differences between runtime and development dependencies.

  • Upload an installable Python package to a package index.

Where do Packages Come From?

All the dependencies we’ve installed previously with pip were written by someone else and uploaded to a Package Index / Repository.

In this session we’ll introduce two different methods for building an installable package from our code. The first, using a tool called Poetry, is the simpler of the two methods, so we’ll walk through the complete packaging process and end up with a package uploaded to the PyPI test site. The second method, using, is the more traditional method and gives us full control, but is more complicated - we won’t cover this fully, but it might be something you want to invesigate further in future.

Packaging our Code with Poetry

Installing Poetry

Before we start this section, let’s make sure again that we don’t have any virtual environments currently activated. If we don’t currently have a virtual environment activated this will give us an error message or tell us to use source deactivate - that’s fine.


The recommended install method for Poetry is similar to the method we used for pyenv. This time it’s a Python script we need to download and run:

curl -sSL | python3 -

If this fails, it’s possible we need to install an extra dependency and try again:

sudo apt install virtualenv
curl -sSL | python3 -

Once Poetry has installed itself, we need to make sure our shell can find it - the install process should give you a line to be added at the bottom of your shell config file. If you’re on Ubuntu, the file we need to add it to is ~/.bashrc and the line should be similar to the one below. If you’re on MacOS, the file will probably be ~/.zshrc and the line to add will be slightly different.

export PATH="$HOME/.local/bin:$PATH"

Once we’ve finished installing, the simplest thing to do here is to just close our terminal and open another one. Then the changes that Poetry makes should have been applied automatically for us.

To test, we can ask where Poetry is installed:

which poetry

If you don’t get this output, then we can try activating it manually and checking again. This would need to be done each time we open a new terminal and want to use Poetry. The file to source might be different depending on your system.

source $HOME/.poetry/env
which poetry

Poetry can also handle virtual environments for us, so in order to behave similarly to how we used them previously, let’s change the Poetry config to put them in the same directory as our project:

poetry config true

Setting up our Poetry Config

Poetry uses a pyproject.toml file to describe the build system and requirements of the package. This file format was described in PEP 518 to solve problems with bootstrapping (the processing we do to prepare to process something) packages using the older convention files and to support a wider range of build tools.

Python Enhancement Proposals

PEP here stands for Python Enhancement Proposals. PEPs are design documents for the Python community, typically specifications or conventions for how to do something in Python, a description of a new feature in Python, etc.

One of the most frequently refered to PEPs is PEP8 which acts as the Python community style guide. This document gives suggestions for how to format our Python code to ensure that it’s easily readable by other developers.

First let’s make sure we’re in the right place:

cd se-day4/code/poetry_project

Because we’re going to use Poetry to manage our dependencies and virtual environment for us, we should deactivate and remove our previous virtual environment to make sure it’s clean and also make sure we’re not using the Python 3.11 version we looked at last session. Remember that when we do deactivate we might get an error or warning if we weren’t already in a virtual environment - this is fine.

rm -rf venv .python-version

Now we’re ready to begin.

To create a pyproject.toml file for our code, we can use poetry init. This will guide us through the most important settings - for each prompt, we either enter our data or accept the default. For the package name, make sure this has some unique identifier in it so it doesn’t match the package name of anyone else - I’ve used my name here, you could use your name, or some random text. This is because, if we want to upload it to the test version of PyPI at the end, it will need to be globally unique. Note that, usually when we’re naming a Python installable package, we use hyphens to separate words.

When we get to the questions about defining our dependencies, we’ll answer no, so we can do this separately later.

poetry init
This command will guide you through creating your pyproject.toml config.

Package name [example]:  inflammation-jgraham
Version [0.1.0]: 0.1.0
Description []:  Example project for using Poetry to build packages
Author [None, n to skip]: James Graham <>
License []:  MIT
Compatible Python versions [^3.8]: ^3.8

Would you like to define your main dependencies interactively? (yes/no) [yes] no
Would you like to define your development dependencies interactively? (yes/no) [yes] no
Generated file

name = "inflammation-jgraham"
version = "0.1.0"
description = "Analyse patient inflammation data"
authors = ["James Graham <>"]
license = "MIT"

python = "^3.8"


requires = ["poetry-core>=1.0.0"]
build-backend = "poetry.core.masonry.api"

Do you confirm generation? (yes/no) [yes] yes

Project Dependencies

Previously, we looked at using a requirements.txt file to define the dependencies of our software. Here, Poetry takes inspiration from package managers in other languages, particularly NPM (Node Package Manager), often used in JavaScript.

Tools like Poetry and NPM understand that there are two different types of dependency: runtime dependencies and development dependencies. Runtime dependencies are those dependencies that need to be installed for our code to run, like NumPy. Development dependencies are dependencies which are an essential part of your development process for a project, but are not required to run it. Common examples of developments dependencies are linters and test frameworks, like Pylint or Pytest.

When we add a dependency using Poetry, Poetry will add it to the list of dependencies in the pyproject.toml file, add a reference to it in a new poetry.lock file, and automatically install the package into our virtual environment. If we don’t yet have a virtual environment, Poetry will create it for us - using the name .venv, so it appears hidden unless we do ls -a. The pyproject.toml file has two separate lists, allowing us to distinguish between runtime and development dependencies.

poetry add matplotlib numpy~=1.20.0
poetry add --dev pylint
poetry install

These two sets of dependencies will be used in different circumstances. When we build our installable package and upload it to a package index, Poetry will only include references to our runtime dependencies. This is because someone installing our software through a tool like pip is using it, but probably doesn’t intend to contribute to the development of our software.

In contrast, if someone downloads our code from GitHub, with our pyproject.toml and installs the project using that, they will get both our runtime and our development dependencies. If someone is downloading our source code, that suggests that they intend to contribute to the development of it, so they’ll need all of our development tools.

Have a look at the pyproject.toml file again to see what’s changed.

Packaging Our Code

Next, we need to make sure that our code is organised in the recommended Python code package structure. This is the package (yes, we use the same word to mean two different things…) structure that we encountered in the refactoring section - a directory containing an and our Python source code files.

We’ve provided an example of a semi-realistic Python application in the code directory for today. You’ll have to rename this package so that it matches the name you told Poetry about, but with underscores instead of hyphens. By convention installable package (the type we install with pip) names use hyphens, whereas code package (a directory of Python files) names use underscores. While we could choose to use underscores in an installable package name, we cannot use hyphens in a code package name, as Python will interpret them as a minus sign when we try to import them.

mv inflammation inflammation_jgraham

Once we’ve got our pyproject.toml configuration done and our code in the right structure, we can go ahead and build a distributable version of our software:

poetry build

This should produce two files for us in the dist directory. The one we care most about is the .whl or wheel file. This is the file that pip uses to distribute and install Python packages, so this is the file we’d need to share with other people who want to install our software.

Now if we gave this wheel file to someone else, they could install it using pip - you don’t need to run this command yourself, you’ve already installed it using poetry install above.

pip3 install dist/poetry_project*.whl

The star in the line above is a wildcard, that means Bash should use any filenames that match that pattern, with any number of characters in place for the star. We could also rely on Bash’s autocomplete functionality and type dist/poetry_project, then hit the Tab key.

Sharing Our Package With The World

The final step in distributing our code is to upload it to a package index. To help us test our packages, PyPI provides a test index at that we can use. Packages uploaded to the test index aren’t accessible to a normal pip install, so no one’s going to accidentally install our software yet.

Firstly, we need to create an account at Click the register link to the top right, and fill in your account details. Once you’ve created your account, click the link to request a verification email and then click the link in the email to verify your account.

Now, we need to tell Poetry about our account on the test PyPI server. Replace your_pypi_username with your actual username. When we enter the second of the following commands, Poetry will also ask us to enter our password:

poetry config repositories.testpypi
poetry config http-basic.testpypi your_pypi_username

Security Alert!

Since we’re publishing our code for other people to use, we need to take care to do this securely. If someone gets access to our PyPI account, they could potentially upload a malicious version of one of our packages. This has happened with several JavaScript packages in the past.

To improve our security, we should use an API key / token rather than a username and password.

For more information, see the PyPI FAQs.

Finally, we’re ready to go. To publish the our software that we’ve been working so hard on, there’s just one more command:

poetry publish -r testpypi

If we now go to and search for our package name, we should find our newly published software. If it’s not there yet, try again in a minute - it sometimes takes a couple of minutes to show up. We can even install this package ourselves using pip, but we need to tell pip to use the testing version of PyPI and make sure we’ve got rid of the previous installation. In this example, replace your_package_name with the name of your package from pyproject.toml

source .venv/bin/activate
pip3 uninstall your_package_name
pip3 install -i your_package_name

Note that there is a space between the URL and your package name in the line above.

After we’ve been working on our code for a while and want to publish an update, we just need to update the version number in the pyproject.toml file (using SemVer perhaps), then use Poetry to build and publish the new version. If we don’t increment the version number, people might end up using this version, even though they thought they were using the previous one. Any re-publishing of the package, no matter how small the changes, needs to come with a new version number.

poetry build
poetry publish -r testpypi

In addition to the commands we’ve already seen, Poetry contains a few more that can be useful for our development process. For the full list see the Poetry CLI documentation.

If you’ve made it this far, congratulations, you’ve successfully published and installed a Python package! Though it’s becoming increasingly common for academic software to be shared under an open source license, not many people go this extra step and make their code installable so easily. Remember that the easier we make it for people to use our code and get involved with the project, the easier it is for people to reproduce and build upon our work. Funders are also starting to put greater emphasis on sharing the outputs of our projects as this increases the impact of our work and the impact of their money.

Adding Some Detail

Using the Poetry documentation, investigate how we might go about adding more detail to our page on the package index website. We want people to be able to find our package and to be able to tell if it’s going to be useful to them. What extra information can we add to the pyproject.toml file to help with this?

What If We Need More Control?

Sometimes we need more control over the process of building our installable package than Poetry allows. In these cases, we have to use the method that existed before Poetry - a file. Because this is a Python file, we can use the full power of Python to describe how to setup our project.

One of the common cases where this is particularly useful is if our project has components in different languages. For example, to speed up some of the core parts we might write some of our functions in C, then call these from our Python code. Using a gives us the flexibility to handle building these components in different ways and bring them together at the end.

In the template repository for one of the SABS mini-projects, we have an example of a basic, general purpose file. You can find this file

Our Own (Optional)

Compare this example file to the Poetry pyproject.toml file we created previously. At the bottom, in the arguments to the setup function, we have many of the same pieces of metadata.

The Python Packaging User Guide provides documentation on the details of packaging a project using In this guide, they use Twine to upload the package to PyPI, instead of Poetry as we did previously.

Using the example file and this documentation, can you produce a file for our Poetry project?

Which configuration style do you prefer for projects like this one?

Key Points

  • Poetry allows us to produce an installable package and upload it to a package index.

  • Making our software installable with pip makes it easier for others to start using it.

  • For complete control over building a package, we can use a file.