Experimental Bazel Python Rules

Status: This is ALPHA software.

Rules

• pip_import
• py_library
• py_binary
• py_test

Overview

This repository provides Python rules for Bazel. Currently, support for
rules that are available from Bazel core are simple aliases to that bundled
functionality. On top of that, this repository provides support for installing
dependencies typically managed via pip.

Setup

Add the following to your WORKSPACE file to add the external repositories:

git_repository(
    name = "io_bazel_rules_python",
    remote = "https://github.com/bazelbuild/rules_python.git",
    # NOT VALID!  Replace this with a Git commit SHA.
    commit = "{HEAD}",
)

# Only needed for PIP support:
load("@io_bazel_rules_python//python:pip.bzl", "pip_repositories")

pip_repositories()

Then in your BUILD files load the python rules with:

load(
  "@io_bazel_rules_python//python:python.bzl",
  "py_binary", "py_library", "py_test",
)

py_binary(
  name = "main",
  ...
)

Importing pip dependencies

These rules are designed to have developers continue using requirements.txt
to express their dependencies in a Python idiomatic manner. These dependencies
are imported into the Bazel dependency graph via a two-phased process in
WORKSPACE:

load("@io_bazel_rules_python//python:pip.bzl", "pip_import")

# This rule translates the specified requirements.txt into
# @my_deps//:requirements.bzl, which itself exposes a pip_install method.
pip_import(
   name = "my_deps",
   requirements = "//path/to:requirements.txt",
)

# Load the pip_install symbol for my_deps, and create the dependencies'
# repositories.
load("@my_deps//:requirements.bzl", "pip_install")
pip_install()

Consuming pip dependencies

Once a set of dependencies has been imported via pip_import and pip_install
we can start consuming them in our py_{binary,library,test} rules. In support
of this, the generated requirements.bzl also contains a requirement method,
which can be used directly in deps=[] to reference an imported py_library.

load("@my_deps//:requirements.bzl", "requirement")

py_library(
    name = "mylib",
    srcs = ["mylib.py"],
    deps = [
        ":myotherlib",
	# This takes the name as specified in requirements.txt
	requirement("importeddep"),
    ]
)

Canonical whl_library naming

It is notable that whl_library rules imported via pip_import are canonically
named, following the pattern: pypi__{distribution}_{version}. Characters in
these components that are illegal in Bazel label names (e.g. -, .) are
replaced with _.

This canonical naming helps avoid redundant work to import the same library
multiple times. It is expected that this naming will remain stable, so folks
should be able to reliably depend directly on e.g. @pypi__futures_3_1_1//:pkg
for dependencies, however, it is recommended that folks stick with the
requirement pattern in case the need arises for us to make changes to this
format in the future.

"Extras"
will have a target of the extra name (in place of pkg above).

Updating docs/

All of the content (except BUILD) under docs/ is generated. To update the
documentation simply run this in the root of the repository:

./update_docs.sh

Updating tools/

All of the content (except BUILD) under tools/ is generated. To update the
documentation simply run this in the root of the repository:

./update_tools.sh