Poetry: Manage Python dependencies and packages

Introduction

In our recent fastapi project, we used poetry as a dependency management tool and we're very happy about it. Although the Poetry site is very well documented, I wanted to log my thoughts about it.

What is Poetry

Poetry is a tool for dependency management and packaging in Python. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you. It also provides a way to create and manage a virtual environment to run a program. Poetry can be used as a replacement for conda to manage packages and virtual environments.

How to install and use it

Details installation instruction are here.

Once installed, create a new project using the following command:

poetry new poetry-demo

once done it will spit out the following structure:

poetry-demo
├── pyproject.toml
├── README.rst
├── poetry_demo
│   └── __init__.py
└── tests
    ├── __init__.py
    └── test_poetry_demo.py

A Couple of gotchas:

1. Poetry can't fully manage Python versions on its own using the version specified in the pyproject.toml. If on the host machine, there are a couple of versions of python have been installed, it will use the default python version to create the virtual environment. The Workaround is to use pyenv or some other tool to manage multiple python versions, or you can use poetry env use path/to/python to create a virtual environment.

2. Poetry is slow (not its fault), so if your project has complex dependencies, the first install will be pretty slow so don't get frustrated.

How to run a python program

Let us install the dependencies by running the following command:

poetry install

This command will also create a virtual environment for you which is great. Now let's add a hellopoetry.py in the root directory and add the following code:

print("Hello Poetry")

Now execute this script using the following command:

 poetry run python hellopoetry.py

and voila!! you have run a basic python script using poetry.

How to add packages

Add the requests package in to project by using this command:

 poetry add requests

Although we do have not a specified version in the above command, Poetry has done a great job finding the correct version for it. Thanks to its fast dependency resolver!!!

Remove the package from the project by using this command:

 poetry add requests

Add a specific version to the project by using this command:

 poetry add  requests=^2.28.0

Add a specific version to the project by modifying pyproject.toml:

 //Add dependencies manually and then run the following command
 poetry update

Summary

If you are starting a new project, Poetry is definitely a choice to manage packages and dependencies