Python GN Templates#

pw_build: Integrations for Bazel, GN, and CMake

The Python build is implemented with GN templates defined in pw_build/python.gni. See the .gni file for complete usage documentation.

See also

Python Base Templates#

The core subset of templates where you can create Python packages, actions, scripts and group them together are listed below.

pw_python_package#

The main Python template is pw_python_package. Each pw_python_package target represents a Python package. As described in pw_python_package targets, each pw_python_package expands to several subtargets. In summary, these are:

  • <name> - Represents the files themselves

  • <name>.lint - Runs static analysis

  • <name>.tests - Runs all tests for this package

  • <name>.install - Installs the package

  • <name>.wheel - Builds a Python wheel

GN permits using abbreviated labels when the target name matches the directory name (e.g. //foo for //foo:foo). For consistency with this, Python package subtargets are aliased to the directory when the target name is the same as the directory. For example, these two labels are equivalent:

//path/to/my_python_package:my_python_package.tests
//path/to/my_python_package:tests

The actions in a pw_python_package (e.g. installing packages and running Pylint) are done within a single GN toolchain to avoid duplication in multi-toolchain builds. This toolchain can be set with the pw_build_PYTHON_TOOLCHAIN GN arg, which defaults to $dir_pw_build/python_toolchain:python.

Note

By default, <name>.lint and <name>.tests will transitively test and lint any dependencies. This is done for backwards compatibility, but if you don’t rely on this behavior you should turn this off by adding pw_build_TEST_TRANSITIVE_PYTHON_DEPS = false to your project’s .gn file.

Arguments#

  • setup - List of setup file paths (setup.cfg and pyproject.toml), which must all be in the same directory.

  • generate_setup: As an alternative to setup, generate setup files with the keywords in this scope. name is required. This follows the same structure as a setup.cfg file’s declarative config For example:

    generate_setup = {
  metadata = {
    name = "a_nifty_package"
    version = "1.2a"
  }
  options = {
    install_requires = [ "a_pip_package" ]
  }
}

  • sources - Python sources files in the package.

  • tests - Test files for this Python package.

    Tip

    It is best to keep these files within the same folder as the BUILD.gn and not nested within another folder that contains an __init__.py file. That could cause your tests to be included within the package distributions (See pw_python_distribution). For example pip installed into the bootstrapped Python virtual environment or as part of a Python wheel.

    If you need to nest your test source files under a sub-folder exclude it in the setup.cfg file with:

    [options]
packages = find:

# Exclude the tests and test_scripts folders.
[options.packages.find]
exclude =
    tests
    test_scripts

  • python_deps - Dependencies on other pw_python_packages in the GN build.

  • python_test_deps - Test-only pw_python_package dependencies.

  • other_deps - Dependencies on GN targets that are not pw_python_packages.

  • inputs - Other files to track, such as package_data.

  • proto_library - A pw_proto_library target to embed in this Python package. generate_setup is required in place of setup if proto_library is used. See Adding Python proto modules to an existing package.

  • static_analysis List of static analysis tools to run; "*" (default) runs all tools. The supported tools are "mypy" and "pylint".

  • pylintrc - Optional path to a pylintrc configuration file to use. If not provided, Pylint’s default rcfile search is used. Pylint is executed from the package’s setup directory, so pylintrc files in that directory will take precedence over others.

  • mypy_ini - Optional path to a mypy configuration file to use. If not provided, mypy’s default configuration file search is used. mypy is executed from the package’s setup directory, so mypy.ini files in that directory will take precedence over others.

Example#

This is an example Python package declaration for a pw_my_module module.

import("//build_overrides/pigweed.gni")

import("$dir_pw_build/python.gni")

pw_python_package("py") {
  setup = [
    "pyproject.toml",
    "setup.cfg",
  ]
  sources = [
    "pw_my_module/__init__.py",
    "pw_my_module/alfa.py",
    "pw_my_module/bravo.py",
    "pw_my_module/charlie.py",
  ]
  tests = [
    "alfa_test.py",
    "charlie_test.py",
  ]
  python_deps = [
    "$dir_pw_status/py",
    ":some_protos.python",
  ]
  python_test_deps = [ "$dir_pw_build/py" ]
  pylintrc = "$dir_pigweed/.pylintrc"
}

pw_python_action#

The pw_python_action template is a convenience wrapper around GN’s action function for running Python scripts. See pw_python_action in the pw_build documentation for usage.

pw_python_script#

A pw_python_script represents a set of standalone Python scripts and/or tests. These files support all of the arguments of pw_python_package except those setup. These targets can be installed, but this only installs their dependencies.

pw_python_script allows creating a pw_python_action associated with the script. To create an action, pass an action scope to pw_python_script. If there is only a single source file, it serves as the action’s script by default.

An action in pw_python_script can always be replaced with a standalone pw_python_action, but using the embedded action has some advantages:

  • The embedded action target bridges the gap between actions and Python targets. A Python script can be expressed in a single, concise GN target, rather than in two overlapping, dependent targets.

  • The action automatically depends on the pw_python_script. This ensures that the script’s dependencies are installed and the action automatically reruns when the script’s sources change, without needing to specify a dependency, a step which is easy to forget.

  • Using a pw_python_script with an embedded action is a simple way to check an existing action’s script with Pylint or Mypy or to add tests.

pw_python_group#

Represents a group of pw_python_package and pw_python_script targets. These targets do not add any files. Their subtargets simply forward to those of their dependencies.

pw_python_group("solar_system_python_packages") {
  python_deps = [
    "//planets/mercury/py",
    "//planets/venus/py",
    "//planets/earth/py",
    "//planets/mars/py",
    "//planets/jupiter/py",
    "//planets/saturn/py",
    "//planets/uranus/py",
    "//planets/neptune/py",
    "//planetoids/ceres/py",
    "//planetoids/pluto/py",
  ]
}

Python Environment Templates#

Templates that manage the Python build and bootstrap environment are listed here.

pw_python_venv#

Defines and creates a Python virtualenv. This template is used by Pigweed in https://cs.pigweed.dev/pigweed/+/main:pw_env_setup/BUILD.gn to create a virtualenv for use within the GN build that all Python actions will run in.

Example#

Example of a typical Python venv definition in a top level BUILD.gn#
declare_args() {
  pw_build_PYTHON_BUILD_VENV = "//:my_build_venv"
}

pw_python_group("my_product_packages") {
  python_deps = [
    "//product_dev_tools/py",
    "//product_release_tools/py",
  ]
}

pw_python_venv("my_build_venv") {
  path = "$root_build_dir/python-build-venv"
  constraints = [ "//tools/constraints.list" ]
  requirements = [ "//tools/requirements.txt" ]
  source_packages = [
    "$dir_pw_env_setup:core_pigweed_python_packages",
    "//tools:another_pw_python_package",
    "//:my_product_packages",
  ]
  pip_generate_hashes = true
}

Arguments#

  • path: The directory where the virtualenv will be created. This is relative to the GN root and must begin with “$root_build_dir/” if it lives in the output directory or “//” if it lives in elsewhere.

  • constraints: A list of constraint files used when performing pip install into this virtualenv. By default this is set to the pw_build_PIP_CONSTRAINTS GN arg.

  • requirements: A list of requirements files to install into this virtualenv on creation. By default this is set to the pw_build_PIP_REQUIREMENTS GN arg.

    See also

    For more info on the pw_build_PIP_CONSTRAINTS and pw_build_PIP_REQUIREMENTS GN args see: Third-party Python Requirements and Constraints

  • pip_generate_hashes: (Default: false) Use --generate-hashes When running pip-compile <A list of requirements files to install into this virtualenv> to compute the final requirements.txt

  • source_packages: A list of in-tree pw_python_package or targets that will be checked for external third_party pip dependencies to install into this virtualenv. Note this list of targets isn’t actually installed into the virtualenv. Only packages defined inside the [options] install_requires section of each pw_python_package’s setup.cfg will be pip installed.

    See also

    For an example setup.cfg file see: Configuring setuptools using setup.cfg files

  • output_logs: (Default: true) If this is true then the virtual environment will output to logs.

pw_python_pip_install#

This will pip install pw_python_package targets into the bootstrapped developer environment.

Example#

Example of a typical Python venv definition in a top level BUILD.gn#
pw_python_pip_install("pip_install_my_product_packages") {
  packages = [
    "//product_dev_tools/py",
    "//product_release_tools/py",
  ]
}

Arguments#

  • packages: A list of pw_python_package targets to be pip installed. All packages specified will be installed using a single pip install command with a --constraint argument for each constraint file in the pw_build_PIP_CONSTRAINTS GN arg.

  • editable: If true, –editable is passed to the pip install command.

  • force_reinstall: If true, --force-reinstall is passed to the pip install command.

Python Distributable Templates#

Pigweed also provides some templates to make it easier to bundle Python packages for deployment. These templates are found in pw_build/python_dist.gni.

pw_python_wheels#

Collects Python wheels for one or more pw_python_package targets, plus any additional pw_python_package targets they depend on, directly or indirectly. Note that this does not include Python dependencies that come from outside the GN build, like packages from PyPI, for example. Those should still be declared in the package’s setup.cfg file as usual.

Arguments#

  • packages - List of pw_python_package targets whose wheels should be included; their dependencies will be pulled in as wheels also.

  • directory - Output directory for the collected wheels. Defaults to $target_out_dir/$target_name.

Wheel collection under the hood#

The .wheel subtarget of every pw_python_package generates a wheel (.whl) for the Python package. The pw_python_wheels template figures out which wheels to collect by traversing the pw_python_package_wheels GN metadata key, which lists the output directory for each wheel.

pw_python_zip_with_setup#

Generates a .zip archive suitable for deployment outside of the project’s developer environment. The generated .zip contains Python wheels (.whl files) for one or more pw_python_package targets, plus wheels for any additional pw_python_package targets in the GN build they depend on, directly or indirectly. Dependencies from outside the GN build, such as packages from PyPI, must be listed in packages’ setup.cfg file as usual.

The .zip also includes simple setup scripts for Linux, MacOS, and Windows. The setup scripts automatically create a Python virtual environment and install the whole collection of wheels into it using pip.

Optionally, additional files and directories can be included in the archive. One common example of an additional file to include is a README file with setup and usage instructions for the distributable. A simple ready-to-use README file is available at pw_build/py_dist/README.md.

Arguments#

  • packages - A list of pw_python_package targets whose wheels should be included; their dependencies will be pulled in as wheels also.

  • inputs - An optional list of extra files to include in the generated .zip, formatted the same way as the inputs argument to pw_zip targets.

  • dirs - An optional list of directories to include in the generated .zip, formatted the same was as the dirs argument to pw_zip targets.

Example#

import("//build_overrides/pigweed.gni")

import("$dir_pw_build/python_dist.gni")

pw_python_zip_with_setup("my_tools") {
  packages = [ ":some_python_package" ]
  inputs = [ "$dir_pw_build/python_dist/README.md > /${target_name}/" ]
}

pw_python_distribution#

Generates a directory of Python packages from source files suitable for deployment outside of the project developer environment. The resulting directory contains only files mentioned in each package’s setup.cfg file. This is useful for bundling multiple Python packages up into a single package for distribution to other locations like http://pypi.org.

Arguments#

  • packages - A list of pw_python_package targets to be installed into the build directory. Their dependencies will be pulled in as wheels also.

  • include_tests - If true, copy Python package tests to a tests subdir.

  • extra_files - A list of extra files that should be included in the output. The format of each item in this list follows this convention:

    //some/nested/source_file > nested/destination_file

    • Source and destination file should be separated by >.

    • The source file should be a GN target label (starting with //).

    • The destination file will be relative to the generated output directory. Parent directories are automatically created for each file. If a file would be overwritten an error is raised.

  • generate_setup_cfg - If included, create a merged setup.cfg for all python Packages using either a common_config_file as a base or name and version strings. The common_config_file should contain the required fields in the metadata and options sections as shown in Configuring setup() using setup.cfg files.

    This scope can optionally include:

    • append_git_sha_to_version = true: Append the current git SHA to the package version string after a + sign.

    • append_date_to_version = true: Append the current date to the package version string after a + sign.

    • include_default_pyproject_file = true: Include a standard pyproject.toml file in the output.

    • include_extra_files_in_package_data = true: Add any extra_files entries to the generated setup.cfg file under the [options.package_data] section.

    • auto_create_package_data_init_py_files = true: (Default: true) Create __init__.py files as needed in all subdirs of extra_files when including in [options.package_data].

    Example using a common setup.cfg and pyproject.toml files.#
    generate_setup_cfg = {
  common_config_file = "pypi_common_setup.cfg"
  append_date_to_version = true
}
extra_files = [
  "//source/pyproject.toml > pyproject.toml"
]
    Example using name and version strings and a default pyproject.toml file.#
    generate_setup_cfg = {
  name = "awesome"
  version = "1.0.0"
  include_default_pyproject_file = true
  append_date_to_version = true
}

Using this template will create an additional target for and building a Python wheel. For example if you define pw_python_distribution("awesome") the resulting targets that get created will be:

  • awesome - This will create the merged package with all source files in place in the out directory under out/obj/awesome/.

  • awesome.wheel - This builds a Python wheel from the above source files under out/obj/awesome._build_wheel/awesome*.whl.

Example#

./pw_env_setup/BUILD.gn#
import("//build_overrides/pigweed.gni")

import("$dir_pw_build/python_dist.gni")

pw_python_distribution("build_python_source_tree") {
  packages = [
    ":some_python_package",
    ":another_python_package",
  ]
  include_tests = true
  extra_files = [
    "//README.md > ./README.md",
    "//some_python_package/py/BUILD.bazel > some_python_package/BUILD.bazel",
    "//another_python_package/py/BUILD.bazel > another_python_package/BUILD.bazel",
  ]
  generate_setup_cfg = {
    common_config_file = "pypi_common_setup.cfg"
    append_git_sha_to_version = true
    append_date_to_version = true
  }
}
./out/obj/pw_env_setup/build_python_source_tree/#
$ tree ./out/obj/pw_env_setup/build_python_source_tree/
├── README.md
├── setup.cfg
├── some_python_package
│   ├── BUILD.bazel
│   ├── __init__.py
│   ├── py.typed
│   ├── some_source_file.py
│   └── tests
│       └── some_source_test.py
└── another_python_package
    ├── BUILD.bazel
    ├── __init__.py
    ├── another_source_file.py
    ├── py.typed
    └── tests
        └── another_source_test.py
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