6.14. Using Python

6.14. Using Python
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The Ports Collection supports parallel installation of multiple Python versions. Ports should make sure to use a correct python interpreter, according to the user-settable PYTHON_VERSION variable. Most prominently, this means replacing the path to python executable in scripts with the value of PYTHON_CMD variable.

Ports that install files under PYTHON_SITELIBDIR should use the pyXY- package name prefix, so their package name embeds the version of Python they are installed into.

PKGNAMEPREFIX= ${PYTHON_PKGNAMEPREFIX}

Table 6.19. Most Useful Variables for Ports That Use Python

`USE_PYTHON`	The port needs Python. Minimal required version can be specified with values such as `2.6+`. Version ranges can also be specified, by separating two version numbers with a dash, e.g.: `2.6-2.7`
`USE_PYDISTUTILS`	Use Python distutils for configuring, compiling and installing. This is required when the port comes with `setup.py`. This overrides the `do-build` and `do-install` targets and may also override `do-configure` if `GNU_CONFIGURE` is not defined.
`PYTHON_PKGNAMEPREFIX`	Used as a `PKGNAMEPREFIX` to distinguish packages for different Python versions. Example: `py24-`
`PYTHON_SITELIBDIR`	Location of the site-packages tree, that contains installation path of Python (usually `LOCALBASE`). The `PYTHON_SITELIBDIR` variable can be very useful when installing Python modules.
`PYTHONPREFIX_SITELIBDIR`	The PREFIX-clean variant of PYTHON_SITELIBDIR. Always use `%%PYTHON_SITELIBDIR%%` in `pkg-plist` when possible. The default value of `%%PYTHON_SITELIBDIR%%` is `lib/python%%PYTHON_VERSION%%/site-packages`
`PYTHON_CMD`	Python interpreter command line, including version number.
`PYNUMERIC`	Dependency line for numeric extension.
`PYNUMPY`	Dependency line for the new numeric extension, numpy. (PYNUMERIC is deprecated by upstream vendor).
`PYXML`	Dependency line for XML extension (not needed for Python 2.0 and higher as it is also in base distribution).
`USE_TWISTED`	Add dependency on twistedCore. The list of required components can be specified as a value of this variable. Example: `web lore pair flow`
`USE_ZOPE`	Add dependency on Zope, a web application platform. Change Python dependency to Python 2.7. Set `ZOPEBASEDIR` containing a directory with Zope installation.

A complete list of available variables can be found in /usr/ports/Mk/bsd.python.mk.

Note that some of the Python applications claim to have DESTDIR support (which would be required for staging) but it is broken (Mailman up to 2.1.16, for instance). This can be worked around by recompiling the scripts. This can be done, for example, in the post-build target. Assuming the Python scripts are supposed to reside in PYTHONPREFIX_SITELIBDIR after installation, the following solution can be applied:

(cd ${STAGEDIR}${PREFIX} \ && ${PYTHON_CMD} ${PYTHON_LIBDIR}/compileall.py \ -d ${PREFIX} -f ${PYTHONPREFIX_SITELIBDIR:S;${PREFIX}/;;})

This recompiles the sources with a path relative to the stage directory, and prepends the value of PREFIX to the file name recorded in the byte-compiled output file by -d. The -f flag is required to force recompilation, and the :S;${PREFIX}/;; strips prefixes from the value of the PYTHONPREFIX_SITELIBDIR variable to make it relative to PREFIX.

This requires Python 2.7 or newer, and does not work with Python 2.6.

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