Python Dependency Manager Companion

# Declaring dependencies It is best practice to declare dependencies in a static file instead of modifying environments with ad-hoc installations. Once dependencies are defined, they can be [locked](./compile.md) to create a consistent, reproducible environment. ## Using `pyproject.toml` The `pyproject.toml` file is the Python standard for defining configuration for a project. To define project dependencies in a `pyproject.toml` file: ```toml title="pyproject.toml" [project] dependencies = [ "httpx", "ruff>=0.3.0" ] ``` To define optional dependencies in a `pyproject.toml` file: ```toml title="pyproject.toml" [project.optional-dependencies] cli = [ "rich", "click", ] ``` Each of the keys defines an "extra", which can be installed using the `--extra` and `--all-extras` flags or `package[<extra>]` syntax. See the documentation on [installing packages](./packages.md#installing-packages-from-files) for more details. See the official [`pyproject.toml` guide](https://packaging.python.org/en/latest/guides/writing-pyproject-toml/) for more details on getting started with a `pyproject.toml`. ## Using `requirements.in` It is also common to use a lightweight `requirements.txt` format to declare the dependencies for the project. Each requirement is defined on its own line. Commonly, this file is called `requirements.in` to distinguish it from `requirements.txt` which is used for the locked dependencies. To define dependencies in a `requirements.in` file: ```python title="requirements.in" httpx ruff>=0.3.0 ``` Optional dependencies groups are not supported in this format.