:::{default-domain} bzl
:::

# Lock

:::{note}
Currently `rules_python` only supports `requirements.txt` format.
:::

## requirements.txt

### pip compile

Generally, when working on a Python project, you'll have some dependencies that themselves have
other dependencies. You might also specify dependency bounds instead of specific versions.
So you'll need to generate a full list of all transitive dependencies and pinned versions
for every dependency.

Typically, you'd have your project dependencies specified in `pyproject.toml` or `requirements.in`
and generate the full pinned list of dependencies in `requirements_lock.txt`, which you can
manage with {obj}`compile_pip_requirements`:

```starlark
load("@rules_python//python:pip.bzl", "compile_pip_requirements")

compile_pip_requirements(
    name = "requirements",
    src = "requirements.in",
    requirements_txt = "requirements_lock.txt",
)
```

This rule generates two targets:
- `bazel run [name].update` will regenerate the `requirements_txt` file
- `bazel test [name]_test` will test that the `requirements_txt` file is up to date

Once you generate this fully specified list of requirements, you can install the requirements ([bzlmod](./download)/[WORKSPACE](./download-workspace)).

:::{warning}
If you're specifying dependencies in `pyproject.toml`, make sure to include the `[build-system]` configuration, with pinned dependencies. `compile_pip_requirements` will use the build system specified to read your project's metadata, and you might see non-hermetic behavior if you don't pin the build system.

Not specifying `[build-system]` at all will result in using a default `[build-system]` configuration, which uses unpinned versions ([ref](https://peps.python.org/pep-0518/#build-system-table)).
:::

### uv pip compile (bzlmod only)

We also have experimental setup for the `uv pip compile` way of generating lock files.
This is well tested with the public PyPI index, but you may hit some rough edges with private
mirrors.

For more documentation see {obj}`lock` documentation.