6.16. Using Python

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

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

PKGNAMEPREFIX=	${PYTHON_PKGNAMEPREFIX}

Table 6.23. Most Useful Variables for Ports That Use Python

`USES=python`	The port needs Python. The minimal required version can be specified with values such as `2.7+`. Version ranges can also be specified by separating two version numbers with a dash: `USES=python:3.2-3.3`
`USE_PYTHON=distutils`	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.
`USE_PYTHON=autoplist`	Create the packaging list automatically. This also requires `USE_PYTHON=distutils` to be set.
`USE_PYTHON=concurrent`	The port will use an unique prefix, typically `PYTHON_PKGNAMEPREFIX` for certain directories, such as `EXAMPLESDIR` and `DOCSDIR` and also will append a suffix, the python version from `PYTHON_VER`, to binaries and scripts to be installed. This allows ports to be installed for different Python versions at the same time, which otherwise would install conflicting files.
`PYTHON_PKGNAMEPREFIX`	Used as a `PKGNAMEPREFIX` to distinguish packages for different Python versions. Example: `py27-`
`PYTHON_SITELIBDIR`	Location of the site-packages tree, that contains installation path of Python (usually `LOCALBASE`). `PYTHON_SITELIBDIR` 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).

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

Example 6.10. Makefile for a Simple Python Module

PORTNAME=	sample
PORTVERSION=	1.2.3
CATEGORIES=	devel

MAINTAINER=	john@doe.tld
COMMENT=	Python sample module

USES=		python
USE_PYTHON=	autoplist distutils

.include <bsd.port.mk>

Some 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, this 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. -f is required to force recompilation, and the :S;${PREFIX}/;; strips prefixes from the value of PYTHONPREFIX_SITELIBDIR to make it relative to PREFIX.

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