- 2019-07-26: The canonical name of this repo has been changed from
@io_bazel_rules_python
to just@rules_python
, in accordance with convention. Please update your WORKSPACE file and labels that reference this repo accordingly.
This repository is the home of the core Python rules -- py_library
,
py_binary
, py_test
, and related symbols that provide the basis for Python
support in Bazel. It also contains packaging rules for integrating with PyPI
(pip
). Documentation lives in the
docs/
directory and in the
Bazel Build Encyclopedia.
Currently the core rules are bundled with Bazel itself, and the symbols in this
repository are simple aliases. However, in the future the rules will be
migrated to Starlark and debundled from Bazel. Therefore, the future-proof way
to depend on Python rules is via this repository. SeeMigrating from the Bundled Rules
below.
The core rules are stable. Their implementation in Bazel is subject to Bazel's backward compatibility policy. Once they are fully migrated to rules_python, they may evolve at a different rate, but this repository will still follow semantic versioning.
The packaging rules (pip_import
, etc.) are less stable. We may make breaking
changes as they evolve. There are no guarantees for rules underneath the
experimental/
directory.
To import rules_python in your project, you first need to add it to your
WORKSPACE
file. If you are using the Bazel
Federation, you will want to
copy the boilerplate in the rules_python release's notes, under the "WORKSPACE
setup" heading. This will look something like the following:
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
name = "rules_python",
# NOT VALID: Replace with actual version and SHA.
url = "https://github.com/bazelbuild/rules_python/releases/download/<RELEASE>/rules_python-<RELEASE>.tar.gz",
sha256 = "<SHA>",
)
load("@rules_python//python:repositories.bzl", "py_repositories")
py_repositories()
# Only needed if using the packaging rules.
load("@rules_python//python:pip.bzl", "pip_repositories")
pip_repositories()
Otherwise, you may import rules_python in a standalone way by copying the following:
load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
git_repository(
name = "rules_python",
remote = "https://github.com/bazelbuild/rules_python.git",
# NOT VALID: Replace with actual Git commit SHA.
commit = "{HEAD}",
)
load("@rules_python//python:repositories.bzl", "py_repositories")
py_repositories()
# Only needed if using the packaging rules.
load("@rules_python//python:pip.bzl", "pip_repositories")
pip_repositories()
Either way, you can then load the core rules in your BUILD
files with:
load("@rules_python//python:defs.bzl", "py_binary")
py_binary(
name = "main",
...
)
The packaging 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("@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()
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"),
]
)
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).
The core rules are currently available in Bazel as built-in symbols, but this
form is deprecated. Instead, you should depend on rules_python in your
WORKSPACE file and load the Python rules from @rules_python//python:defs.bzl
.
A buildifier
fix is available to automatically migrate BUILD and .bzl files to add the
appropriate load()
statements and rewrite uses of native.py_*
.
# Also consider using the -r flag to modify an entire workspace.
buildifier --lint=fix --warnings=native-py <files>
Currently the WORKSPACE file needs to be updated manually as per Getting started above.
Note that Starlark-defined bundled symbols underneath
@bazel_tools//tools/python
are also deprecated. These are not yet rewritten
by buildifier.
The content underneath docs/
is generated. To update the documentation,
simply run this in the root of the repository:
./update_docs.sh
The piptool.par
and whltool.par
files underneath tools/
are compiled
versions of the Python scripts under the packaging/
directory. We need to
check in built artifacts because they are executed during WORKSPACE
evaluation, before Bazel itself is able to build anything from source.
The .par files need to be regenerated whenever their sources are updated. This can be done by running
# You can pass --nodocker if Docker is not available on your system.
./update_tools.sh
from the repository root. However, since these files contain compiled code, we do not accept commits that modify them from untrusted sources.1 If you submit a pull request that modifies the sources and we accept the changes, we will regenerate these files for you before merging.
1 See "Reflections on Trusting Trust".