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22.4.7 Python Modules

We currently package Python 2 and Python 3, under the Scheme variable names python-2 and python as explained in Version Numbers. To avoid confusion and naming clashes with other programming languages, it seems desirable that the name of a package for a Python module contains the word python.

Some modules are compatible with only one version of Python, others with both. If the package Foo is compiled with Python 3, we name it python-foo. If it is compiled with Python 2, we name it python2-foo. Packages should be added when they are necessary; we don’t add Python 2 variants of the package unless we are going to use them.

If a project already contains the word python, we drop this; for instance, the module python-dateutil is packaged under the names python-dateutil and python2-dateutil. If the project name starts with py (e.g. pytz), we keep it and prefix it as described above.

Note: Currently there are two different build systems for Python packages in Guix: python-build-system and pyproject-build-system. For the longest time, Python packages were built from an informally specified file. That worked amazingly well, considering Python’s success, but was difficult to build tooling around. As a result, a host of alternative build systems emerged and the community eventually settled on a formal standard for specifying build requirements. pyproject-build-system is Guix’s implementation of this standard. It is considered “experimental” in that it does not yet support all the various PEP-517 build backends, but you are encouraged to try it for new Python packages and report any problems. It will eventually be deprecated and merged into python-build-system. Specifying Dependencies

Dependency information for Python packages is usually available in the package source tree, with varying degrees of accuracy: in the pyproject.toml file, the file, in requirements.txt, or in tox.ini (the latter mostly for test dependencies).

Your mission, when writing a recipe for a Python package, is to map these dependencies to the appropriate type of “input” (see inputs). Although the pypi importer normally does a good job (see Invoking guix import), you may want to check the following check list to determine which dependency goes where.

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