governance/reference/pti/python.rst

Project Testing Interface: Python

Each project containing Python components must be able to do:

• Unit tests for Python (see below for version details)
• Codestyle checks
• Testing Coverage Report
• Source Tarball Generation
• Translations import/export and merge for translated projects
• Documentation generation

Specific commands

To drive the above tasks, the following commands should be supported in a clean tree:

• tox -e pep8
• tox -e cover
• python -m build -s . (sdist)
• python -m build -w . (wheels)
• sphinx-build -W -b html doc/source doc/build

The Python 3 version may change from cycle to cycle. Projects should target the following, extending supported Python 3.x with the tested Python 3 runtimes <pti-tested-runtimes> for the current development cycle:

• tox -e py3x

Projects should avoid removing Python versions that have not reached End Of Life without a solid reason. It is recommended to keep compatibility with older Python versions as long as possible. While CI coverage of Python versions that are not mentioned in PTI can be reduced, such reduction is not mandatory.

Projects that are translated should also support generating and updating their Portable Object Template (``.pot``) files using the following commands:

• pybabel extract
• pybabel update

Some basic prerequisites for test running (system packages, database configuration, custom filesystem types) are acceptable as long as they are documented in a visible location such as a CONTRIBUTING.rst, TESTING.rst, or README.rst file in the root of the repository.

Requirements Listing

Each project should list its required dependencies in either project.dependencies in pyproject.toml or in a requirements.txt file, while additional dependencies required for testing should be listed in the test key of project.optional-dependencies in pyproject.toml or in a test-requirements.txt file. Environment marker should be used if there are requirements that are specific to a given Python version, platform (Windows, Linux, ...), or implementation (cpython, pypy, ...)

Constraints

The requirements project maintains a set of constraints with packages pinned to specific package versions that are known to be working. The goal is to ease the diagnosis of breakage caused by projects upstream to OpenStack and to provide a set of packages known to work together.

Projects may opt into using the constraints in one or more of their standard targets via their tox.ini configuration.

Virtual Environment Management

To support sensible testing across multiple Python versions, we use tox config files in the projects.

Python test running

OpenStack uses stestr as its test runner. stestr should be used for running all Python tests, including unit, functional, and integration tests. stestr is used because of its real time subunit output and its support for parallel execution of tests. In addition, stestr only runs tests conforming to the Python stdlib unittest model (and extensions on it like testtools). This enables people to use any test runner they prefer locally. Other popular test runners often include a testing ecosystem which is tied directly to the runner. Using these precludes the use of alternative runners for other users.

To have a consistent interface via tox between projects' unit test jobs the command for running stestr in tox should be set like so:

[testenv]
commands =
    stestr run {posargs}

Note

While the use of wrapper scripts can sometimes be useful as a short term crutch to work around a specific temporary issues, it should be avoided because it creates a divergent experience between projects, and can mask real issues.

If there are additional mandatory arguments needed for running a test suite they can be added before the positional arguments, ensuring the end user experience remains the same. For example:

[testenv]
commands =
    stestr --test-path ./tests/unit run {posargs}

However, these arguments should try to be minimized because it just adds to the complexity that people will need to understand when running tests on a project.

Coverage Jobs

For coverage jobs you need to invoke the test runner in the same way as for the normal unit test jobs, but to switch the Python executable to be coverage run. To do this you need to setup the tox cover job like:

[testenv:cover]
setenv =
    PYTHON=coverage run --source $project --parallel-mode
commands =
    stestr run {posargs}
    coverage combine
    coverage html -d cover
    coverage xml -o cover/coverage.xml

Specifically, the output html directory cover and the coverage.xml file added to that directory are mandatory output artifacts.

Project Configuration

All OpenStack projects use pbr for consistent operation of setuptools. To accomplish this, all setup.py files only contain a simple setup function that enabled pbr. Actual project configuration is then handled in pyproject.toml or setup.cfg.

Generated Files

ChangeLog and AUTHORS files are generated at setup.py sdist time. This is handled by pbr.

.mailmap files should exist where a developer has more than one email address or identity, and should map to the developer's canonical identity.

Translations

To support translations processing, projects should have a valid babel config. There should be a locale package inside of the top project module, and in that directory should be the $project.pot file. For instance, the .pot file for nova should be found at nova/locale/nova.pot. Babel commands should be configured out output their .mo files in to $project/locale as well.

Release Notes

As a convenience for developers, it is recommended that projects provide a releasenotes environment for tox that will run

sphinx-build -a -E -W -d releasenotes/build/doctrees -b html \
    releasenotes/source releasenotes/build/html

The project infrastructure will not use tox -e releasenotes to build the documentation. Therefore it is STRONGLY discouraged for people to put additional logic into the command section of that tox environment. Additional logic needed around release notes generation should go into reno.