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mgorny 12/11/04 14:05:12 |
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Added: user-guide.xml |
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Log: |
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Initial version of python-r1 user guide. |
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Revision Changes Path |
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1.1 xml/htdocs/proj/en/Python/python-r1/user-guide.xml |
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file : http://sources.gentoo.org/viewvc.cgi/gentoo/xml/htdocs/proj/en/Python/python-r1/user-guide.xml?rev=1.1&view=markup |
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plain: http://sources.gentoo.org/viewvc.cgi/gentoo/xml/htdocs/proj/en/Python/python-r1/user-guide.xml?rev=1.1&content-type=text/plain |
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Index: user-guide.xml |
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=================================================================== |
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<?xml version="1.0" encoding="UTF-8"?> |
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> |
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/proj/en/Python/python-r1/user-guide.xml,v 1.1 2012/11/04 14:05:12 mgorny Exp $ --> |
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|
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<guide lang="en"> |
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<title>python-r1 User's Guide</title> |
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|
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<author title="Author"> |
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<mail link="mgorny@g.o">Michał Górny</mail> |
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</author> |
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|
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<author title="Editor"> |
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<mail link="idella4@g.o">Ian Delaney</mail> |
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</author> |
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|
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<abstract> |
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This guide provides a basic insight to how Python packages |
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are deployed using the python-r1 eclasses. It describes |
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the multi-implementation concept and offers a guide to selecting |
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preferred implementations. |
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</abstract> |
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|
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<!-- The content of this document is licensed under the CC-BY-SA license --> |
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<!-- See http://creativecommons.org/licenses/by-sa/3.0/ --> |
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<license version="3.0"/> |
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|
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<version>1</version> |
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<date>2012-11-04</date> |
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|
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<chapter id="Multi_implementation_support"> |
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<title>Multi-implementation support</title> |
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|
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<section id="mis_Short_introduction"> |
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<title>Short introduction</title> |
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|
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<body> |
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<p> |
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Currently Gentoo supports three different Python interpreters |
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— CPython, PyPy and Jython. CPython has two major but distinct |
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branches — called simply Python 2 & Python 3. This makes |
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four <e>interpreter groups</e>. |
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</p> |
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|
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<p> |
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Each group is further sub-divided into branches, which |
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are identified by minor version numbers: Python 2.7, 2.6, 2.5, |
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3.3, 3.2, 3.1; PyPy 1.9 and 1.8; and lastly, Jython 2.5. All |
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these versions can be installed in Gentoo side-by-side, and are |
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collectively referred to as <e>Python implementations</e>. |
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</p> |
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|
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<p> |
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There may be various reasons to install multiple Python |
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implementations. The most important is incompatibilities |
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that occur between each one's Python scripts. Many Python |
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packages in Gentoo still don't support Python 3. There are also |
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a few packages which support only Python 3. |
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</p> |
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|
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<p> |
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Having two or more implementations installed allows our users |
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to run all kinds of scripts. Another common and significant |
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advantage of having multiple Python versions installed |
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is the ability to test a script against multiple interpreters. |
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</p> |
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</body> |
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</section> |
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|
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<section id="mis_PYTHON_TARGETS_setting"> |
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<title>PYTHON_TARGETS setting</title> |
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|
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<body> |
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<p> |
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Having a number of implementations to choose from, the modern |
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Python packages provide users with an ability to explicitly |
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select one or more Python implementations. This selection |
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is performed through the use of <c>PYTHON_TARGETS</c> expanded |
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USE flags. |
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</p> |
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|
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<pre caption="Example output of emerge with PYTHON_TARGETS-aware |
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package"> |
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$ <i>emerge -pv app-portage/flaggie</i> |
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These are the packages that would be merged, in order: |
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Calculating dependencies... done! |
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[<keyword>ebuild R *</keyword>] <ident>app-portage/flaggie-9999::mgorny</ident> <var>PYTHON_TARGETS</var>="<const>python2_6 python2_7 python3_2</const> <comment>-python3_1</comment>" 0 kB |
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|
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Total: 1 package (1 reinstall), Size of downloads: 0 kB |
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</pre> |
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<p> |
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As you can see in the above sample, the package in question |
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supports four Python implementations of which three are enabled. |
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This means that all the Python modules and scripts will be |
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installed for those three Python versions, and thus they will |
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be available to the scripts run using those versions. |
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</p> |
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|
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<p> |
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CPython versions 2.7 and 3.2 are enabled by default. If you wish |
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to use a different set of enabled implementations, you have |
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to set the <c>PYTHON_TARGETS</c> variable |
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in <path>make.conf</path>. Please note that it is |
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not incremental — that is, you need to list all the enabled |
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implementations. |
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</p> |
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|
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<pre caption="Example make.conf enabling Python 2.6, 2.7 and 3.2"> |
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<var>PYTHON_TARGETS</var>=<const>"python2_6 python2_7 python3_2"</const> |
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</pre> |
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</body> |
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</section> |
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|
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<section id="mis_Python_script_renaming"> |
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<title>Python script renaming</title> |
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|
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<body> |
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<p> |
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You may have noticed already that the default installation |
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of Python scripts in Gentoo differs to that of other |
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distributions (and Python packages themselves). This is done |
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in order to completely support multiple Python implementations |
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being used on the same system. |
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</p> |
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|
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<pre caption="Example Python scripts installed by a package"> |
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$ <i>ls -1 /usr/bin/flaggie*</i> |
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<var>/usr/bin/flaggie</var> |
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/usr/bin/flaggie-python2.6 |
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/usr/bin/flaggie-python2.7 |
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/usr/bin/flaggie-python3.2 |
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</pre> |
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<p> |
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Firstly, all Python scripts installed by packages are installed |
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in per-implementation variants. This ensures that any changes |
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necessary for a given Python implementation are preserved |
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in the scripts. It also makes it possible to easily run |
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the script with the desired interpreter. |
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</p> |
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|
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<p> |
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Additionally, in place of the standard script, a wrapper |
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is installed. The wrapper is a very simple tool which checks |
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which of the Python implementations supported by the script |
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would be the preferred one and runs the appropriate script |
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variant. |
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</p> |
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</body> |
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</section> |
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</chapter> |
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|
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<!-- vim:se tw=72 ts=2 sts=2 sw=2 :--> |
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</guide> |
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