Dependency Management with Poetry

Poetry is an essential tool for Python developers as it revolutionizes dependency management, packaging, and project development. It simplifies the process of managing project dependencies by providing a declarative and intuitive approach. With Poetry:

• Developers can easily define and track their project's dependencies, ensuring consistent and reproducible development environments across different machines. Additionally.
• Poetry simplifies packaging by automating the creation of distributable packages, making it easier to share and distribute projects with others.
• It also facilitates the creation of virtual environments, isolating project dependencies and avoiding conflicts. But, please better use specific virtual environment tools to create virtual-environments (pyenv, venv module, conda...)

Poetry's comprehensive features, combined with its user-friendly interface, streamline the development workflow and enhance the overall efficiency and maintainability of Python projects.

Why Poetry if we have plain requirements.txt

While requirements.txt is a simple declaration of needed dependencies with Poetry you can pretty much trust that whatever combination it finds will work. It also allows you to install the local project as a python module using pip (but this is a more advanced topic).

More About Poetry

You can find more info about Poetry in the official documentation.

1. Installing Poetry

Once we have our development environment up and running, we can start creating our project. We will use Poetry to manage our project's dependencies and packaging. Poetry provides a simple and intuitive interface for managing dependencies, packaging, and virtual environments. It also offers a comprehensive set of features, such as dependency resolution, dependency isolation, and dependency locking. Poetry's user-friendly interface and powerful features make it an indispensable tool for Python developers.

How to install poetry?

Open a terminal and use onw of the following.

Using pipUsing the official installer

pip install poetry==<version> # (1)

1. ℹ️ Remember to use a specific version (like 1.4.2, 1.5.0 or 1.6.1) by replacing <version> with the desired version.

curl -sSL https://install.python-poetry.org | python3 - --version <version> # (1)

1. ℹ️ Remember to use a specific version (like 1.4.2, 1.5.0 or 1.6.1) by replacing <version> with the desired version.

Avoid creating a virtualenv using Poetry

As we have seen before, by default Poetry creates a virtual environment for each project, but this is normally handled by other tools like pyenv or conda. So, if you are using Poetry. In order to avoid Poetry creating a virtual environment, you can use the virtualenvs.create config:

poetry config virtualenvs.create false

2. Creating a new project

To create a new project, we can use the new command:

poetry new <project_name>

The default poetry project structure

The poetry new <project_name> command will create a new project with the following structure:

<project_name>
├── pyproject.toml
├── README.md
├── <project_name>
│   └── __init__.py
└── tests
    └── __init__.py

The default pyproject.toml file

The pyproject.toml file contains the project's metadata and dependencies and it will look like this:

[tool.poetry]
name = "<project_name>"
version = "0.1.0"
description = ""
authors = ["<author_name> <author_email>"]
readme = "README.md"
packages = [{include = "<project_name>"}]

[tool.poetry.dependencies]
python = "^<python_version>" # (1)

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

1. The ^ symbol in poetry indicates version is pinned to the major version. Remember: versions are given as MAJOR.MINOR.PATCH. So, if we had, for example ^3.11 as the python version, it means that this project is compatible with any 3.x python version (being x equal or greater than 11) but never 4.x versions.

3.2. Adding dependencies

To add a dependency, we can use the add command:

poetry add <dependency>

How to add a main dependency: requests

This will add the dependency to the pyproject.toml file and install it in the virtual environment. For example, to add the requests library, we can use the following command:

poetry add requests

This will add the following lines to the pyproject.toml file:

[tool.poetry.dependencies]
python = "^3.9"
requests = "^2.25.1"

Adding dependencies just for development

If we want to add a dependency just for development, we can use the --group dev flag. This will add the dependency to the pyproject.toml file under the [tool.poetry.group.dev.dependencies] section.

poetry add <dependency> --group dev

"How to add a development dependency: pytest

For example, to add the pytest library, we can use the following command:

poetry add pytest --group dev

This will add the following lines to the pyproject.toml file:

[tool.poetry.dependencies]
python = "^3.11"

[tool.poetry.group.dev.dependencies]
pytest = "^6.2.2"

3.3. Removing dependencies

To remove a dependency, we can use the remove command:

poetry remove <dependency>