Metadata for Python packging

Overview

Questions

• What is pyproject.toml?

Objectives

• To understand the structure of pyproject.toml

Introduction

---

In the previos lesson, we touched upon pixi.toml briefly. In this lesson, we will learn about pyproject.toml. pyproject.toml is the most common format for Python projects. Please not, for a project maintained using pixi, either of the 2 i.e. pyproject.toml or pixi.toml are fine. You just need to take care of some specific syntaxes.

To add pyproject.toml file, we give the following command :

BASH

pixi init --format pyproject

OUTPUT

✔ Created .../greet_me/pyproject.toml

Whats inside pyproject.toml

---

• Manifest metadata

TOML

[project]
name = "greet_me"
version = "0.1.0"
description = "greet_me Pixi-managed package"
authors = [{ name = "Priyanka", email = "" }]
readme = "README.md"
license = { text = "MIT" }
requires-python = ">=3.11"
dependencies = []

The [build-system] table in a pyproject.toml file tells packaging tools like pip what software is needed to build your Python project. It specifies the build backend that will be used to create distributable packages, like wheels (.whl) or source distributions (.sdist).

This section was introduced by PEP 518 and is essential for modern Python packaging. The [build-system] table has two main keys:

1. requires: This is a list of strings specifying the packages needed to build your project. These packages will be downloaded and installed into a temporary, isolated environment before the build process begins. You must include the build backend itself here.
2. build-backend: This is a string that points to the specific Python object (the “backend”) that packaging tools will use to execute the build. It’s the entry point for creating your project’s packages.

TOML

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

• Editable project install

This means that the package is installed in editable mode, so you can make changes to the package and see the changes reflected in the environment, without having to re-install the environment. The greet_me package itself is added as an editable dependency.

TOML

[tool.pixi.pypi-dependencies]
greet_me = { path = ".", editable = true }

• Dependency handling For dependency management, following lines are necessary in your pyproject.toml file. requires_python tag is used to specify the version of Python.

  [tool.pixi.workspace]: This section controls where packages come from and what platforms Pixi should resolve for. It is also used to define project-wide settings.

  [tool.pixi.pypi-dependencies] : This section is used to delare the dependencies of our project that will be installed via Pip or similar tools from Python Package Index. In short they are libraries necessary for our project and will be installed via pip.

TOML

[project]
name = "greet_me"
requires-python = ">=3.11"

[tool.pixi.workspace]
channels = ["conda-forge"]
platforms = ["linux-64", "win-64"]

[tool.pixi.pypi-dependencies]
requests = ">=2.31.0,<3"

You can specify a range or multiple supported Python versions using the syntax below.

TOML

requires-python = ">=3.11, <3.12"

If you were using pixi.toml file, the equivalent syntax would be

TOML

[tool.pixi.workspace]
name = "greet_me"
channels = ["conda-forge"]
platforms = ["linux-64", "win-64"]

[tool.pixi.pypi-dependencies]
python = ">=3.11"

[tool.pixi.tasks]

• Tasks

Here you can specify various steps that you would want to run before making your package. It ususally lets you define and run custom cammands or scripts for your project.

TOML

[tool.pixi.tasks]
# This command will only be defined on Windows
greet  = { cmd = "echo 'Happy Python Packaging!'" }

Final pyproject.toml should look like this below, for reference.

TOML

[project]
authors = [{name = "Priyanka O"}]
dependencies = []
name = "po_greet_me"
requires-python = ">= 3.11"
version = "0.1.2"
description = "greet_me Pixi-managed package"

[build-system]
build-backend = "hatchling.build"
requires = ["hatchling"]

[tool.hatch.build.targets.wheel]
packages = ["my_package"]

[tool.pixi.workspace]
channels = ["conda-forge"]
platforms = ["linux-64"]

[tool.pixi.pypi-dependencies]
greet_me = { path = ".", editable = true }
requests = ">=2.32.5,<3"

[tool.pixi.tasks]
greet  = { cmd = "echo 'Happy Python Packaging!'" }

Key Points

• Need to have a pyproject.toml file
• Need to have [build-system] section with requires and build-backend specfied.
• Need to have [project] section with atleast name and version specified.
• Nice to have dependencies specified in [project] section.