aspect_rules_py is a layer on top of rules_python, the standard Python ruleset hosted at
https://github.com/bazelbuild/rules_python.
The lower layer of rules_python is currently reused, dealing with the toolchain and dependencies.
However, this ruleset introduces a new implementation of py_library, py_binary, and py_test.
Our philosophy is to behave more like idiomatic python ecosystem tools, where rules_python is closely
tied to the way Google does Python development in their internal monorepo, google3.
| Layer | Legacy | Recommended |
|---|---|---|
| rules: BUILD file UI | rules_python | rules_py |
| gazelle: generate BUILD files | rules_python | rules_python [1] |
| pip_parse: fetch and install deps from pypi | rules_python | rules_python |
| toolchain: fetch hermetic interpreter | rules_python | rules_python |
Need help? This ruleset has support provided by https://aspect.dev.
[1] we will likely fork the extension for performance, using TreeSitter to parse Python code rather than a Python program.
We think you'll love rules_py because:
- The launcher uses the Bash toolchain rather than Python, so we have no dependency on a system interpreter. Fixes:
- We don't mess with the Python
sys.path/$PYTHONPATH. Instead we use the standardsite-packagesfolder layout produced bypip_install. This avoids problems like package naming collisions with built-ins (e.g.collections) or whereargparsecomes from a transitive dependency instead. Fixes: - We run python in isolated mode so we don't accidentally break out of Bazel's action sandbox. Fixes:
- We create a python-idiomatic virtualenv to run actions, which means better compatibility with userland implementations of importlib.
- Thanks to the virtualenv, you can open the project in an editor like PyCharm and have working auto-complete, jump-to-definition, etc. Fixes:
Note
What about the "starlarkification" effort in rules_python?
We think this is only useful within Google, because the semantics of the rules will remain identical. Even though the code will live in bazelbuild/rules_python rather than bazelbuild/bazel, it still cannot change without breaking Google-internal usage, and has all the ergonomic bugs above due to the way the runtime is stubbed.
Follow instructions from the release you wish to use: https://github.com/aspect-build/rules_py/releases
In any ancestor BUILD file of the Python code, add these lines to instruct Gazelle to create rules_py variants of the py_* rules:
# gazelle:map_kind py_library py_library @aspect_rules_py//py:defs.bzl
# gazelle:map_kind py_binary py_binary @aspect_rules_py//py:defs.bzl
# gazelle:map_kind py_test py_test @aspect_rules_py//py:defs.bzl