Packaging:Python

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{{DISPLAYTITLE:Fedora Packaging Guidelines for Python}}
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<div style="float: right;" class="toclimit-2">__TOC__</div>
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== Python Version Support ==
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In Fedora we have multiple Python runtimes, one for each supported major Python release. At this point that's one for python2.x and one for python3.x. If a piece of software supports python3, it must be packaged for python3. If it supports python2 as well, it may be packaged for python2. If it supports only python2 then (obviously) it must not be packaged for python3.
 +
 
== Multiple Python Runtimes ==
 
== Multiple Python Runtimes ==
  
In Fedora we have multiple python runtimes, one for each supported major releaseAt this point that's one for python2.x and one for python3.x
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Each runtime corresponds to a binary of the form <code>/usr/bin/python$MAJOR.$MINOR</code>.  One of these python runtimes is the "system runtime" which is what is run when invoking <code>/usr/bin/python</code>On Fedora 22, for example, this is a link to <code>/usr/bin/python2</code> (which itself is a link to <code>/usr/bin/python2.7</code>).
  
Each runtime corresponds to a binary of the form <code>/usr/bin/python$MAJOR.$MINOR</code>
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However, packages in Fedora should not depend on where <code>/usr/bin/python</code> happens to point but instead should call the proper executable for the needed python major version directly, either <code>/usr/bin/python2</code> or <code>/usr/bin/python3</code> as appropriate.
  
One of these python runtimes is the "system runtime" which is what we run when invoking <code>/usr/bin/python</code>.  On Fedora 13 this is <code>/usr/bin/python-2.6</code>
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All python runtimes have a virtual provide for <code>python(abi) = $MAJOR-$MINOR</code>.  For example, the python-3.4 runtime rpm has:
 
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All python runtimes have a virtual provide for <code>python(abi) = $MAJOR-$MINOR</code>.  For example, the python-3.1 runtime rpm has:
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   $ rpm -q --provides python3 |grep -i abi
 
   $ rpm -q --provides python3 |grep -i abi
   python(abi) = 3.1
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   python(abi) = 3.4
  
 
python modules using these runtimes should have a corresponding "Requires" line on the python runtime that they are used with.  This is done automatically for files below <code>/usr/lib[^/]*/python${PYVER}</code>
 
python modules using these runtimes should have a corresponding "Requires" line on the python runtime that they are used with.  This is done automatically for files below <code>/usr/lib[^/]*/python${PYVER}</code>
  
{{admon/warning|Test your work| Remember to test the built RPMs and verify that they actually work!  For instance, when you're packaging a python module that builds for both python2 and python3, don't test the python2 module but ship the python3 module without testing that it does what it's supposed to.  If you are requesting that an application '''switch''' from Python 2 to Python 3 for its Python implementation, please provide supporting material (e.g. a list of tests performed, and their outcome).  Simply getting a package to build against Python 3 is no guarantee that the package's functionality still works.}}
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Mirroring policy for regular packages, the Python-version-specific subpackages of your package most not be removed in a release branch of Fedora.
 
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{{admon/note|For packagers of the python interpreter|Unlike the Requires lines, the "Provides" for each runtime are manually entered into the specfile for each runtime.  In theory <code>/usr/lib/rpm/pythondeps.sh</code> would also automatically generate "Provides" lines for the runtime, but in practice rpmbuild only invokes it for files in the rpm payload identified as "python" by the <code>file</code> utility, and the runtime is an ELF binary, not a python script, hence it isn't passed.  It's simplest to manually supply the Provides line, rather than change these innards of rpmbuild.  See [[rhbug:532118|Red Hat Bug 532118]].}}
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== BuildRequires ==
 
== BuildRequires ==
To build a package containing python2 files, you need to have
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Packages building for python2 will need <code>BuildRequires: python2-devel</code>.
<pre>
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Packages building for python3 will need <code>BuildRequires: python3-devel</code>.
BuildRequires: python2-devel
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Packages building for for both will need build dependencies on both.
</pre>
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Similarly, when building a package which ships python3 files, you need
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== Provides ==
<pre>
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Using a fictional module named "example", the subpackage containing the python2 version '''must''' provide <code>python2-example</code>.  This is of course always the case if the subpackage is named <code>python2-example</code> (as in the examples below).  If the subpackage has some other name then then <code>Provides: python2-example</code> must be added explicitly (but see the <code>%python_provide</code> macro below).
BuildRequires: python3-devel
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</pre>
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A package that has both python2 and python3 files will need to BuildRequire both.
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The python3 subpackage '''must''' provide <code>python3-example</code>.  However, as the naming guidelines mandate that the python3 subpackage be named <code>python3-example</code>, this will happen automatically.
  
== Macros ==
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=== The %python_provide macro ===
In RHEL 5 and older, python2 packages that install python modules need to define <code>python_sitelib</code> or <code>python_sitearch</code> macros that tell where to find the python directory that modules are installed in.  This is not needed in current Fedora or with python3 modules as the macros are defined by <code>rpm</code> and the <code>python3-devel</code> package.  To define those conditionally you can use this:
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<pre>
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In addition, the subpackage corresponding to the current system runtime '''must''' provide <code>Provides: python-example</code>.  However, the system version of python in Fedora will almost certainly change at some point in the future.
%if 0%{?rhel} && 0%{?rhel} <= 5
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%{!?python_sitelib: %global python_sitelib %(%{__python} -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())")}
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%{!?python_sitearch: %global python_sitearch %(%{__python} -c "from distutils.sysconfig import get_python_lib; print(get_python_lib(1))")}
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%endif
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</pre>
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Note that the use of <code>%{!? [...]}</code> does allow this to work without the check for rhel versions but putting the conditional in documents when we can remove the entire stanza from the spec file.
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To avoid having to alter every python module package when this change happens, and to allow the same spec to build for releases with different system versions of python, a convenient <code>%python_provide</code> macro is provided.  When given (as an argument) the name of the current subpackage, it will evaluate to either the proper <code>Provide:</code> line or nothing at all as appropriate for the version of the system runtime.  Thus if the package follows the suggested subpackage naming scheme as shown in the below example, placing this macro in the definition of each subpackage will guarantee that the necessary <code>Provide:</code> line appears where it should, and does not appear where it shouldn't.
  
In Fedora 13 and greater, the following macros are defined for you:
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Finally, if the <code>%python_provide</code> is called with <code>python-example</code> (no python major version in the name) then it will evaluate to either <code>Provides: python2-example</code> or <code>Provides: python3-example</code> depending on the version of the current system runtime.
{|
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 +
== Macros ==
 +
The following macros are defined for you:
 +
{| class="mw-collapsible mw-collapsed wikitable" style="width:100%"
 
!Macro!!Normal Definition!!Notes
 
!Macro!!Normal Definition!!Notes
 
|-
 
|-
|__python||/usr/bin/python||Python 2 interpreter.  Also the default python interpreter
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|__python||<code>%{__python2}</code>||Default Python interpreter. Currently links to Python2 interpreter
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|-
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|__python2||/usr/bin/python2||Python 2 interpreter.  Also the current default python interpreter
 
|-
 
|-
 
|__python3||/usr/bin/python3||Python 3 interpreter
 
|__python3||/usr/bin/python3||Python 3 interpreter
 
|-
 
|-
|python_sitelib||/usr/lib/python2.X/site-packages||Where pure python2 modules are installed
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|python_provide|| (Lua script) ||Given a package name, evaluates to either <code>Provides: python-example</code> or nothing at all depending on the version of the system runtime. See [[Packaging:Python#The_.25python_provide_macro|here]] for an example.
 
|-
 
|-
|python_sitearch||/usr/lib64/python2.X/site-packages on x86_64<BR>/usr/lib/python2.X/site-packages on x86||Where python2 extension modules that are compiled C are installed
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|python_sitelib||<code>%{python2_sitelib}</code>||Where pure python modules are installed for the default Python implementation
 +
|-
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|python_sitearch||<code>%{python2_sitearch}</code>||Where python extension modules that are compiled C are installed for the default Python implementation
 +
|-
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|python2_sitelib||/usr/lib/python2.X/site-packages||Where pure python2 modules are installed
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|-
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|python2_sitearch||/usr/lib64/python2.X/site-packages on x86_64<BR>/usr/lib/python2.X/site-packages on x86||Where python2 extension modules that are compiled C are installed
 
|-
 
|-
 
|python3_sitelib||/usr/lib/python3.X/site-packages||Where pure python3 modules are installed
 
|python3_sitelib||/usr/lib/python3.X/site-packages||Where pure python3 modules are installed
Line 58: Line 63:
 
|python3_sitearch||/usr/lib64/python3.X/site-packages on x86_64<BR>/usr/lib/python3.X/site-packages on x86||Where python3 extension modules that are compiled C are installed
 
|python3_sitearch||/usr/lib64/python3.X/site-packages on x86_64<BR>/usr/lib/python3.X/site-packages on x86||Where python3 extension modules that are compiled C are installed
 
|-
 
|-
|py3dir||%{_builddir}/python3-%{name}-%{version}-%{release}||Directory to use when building python3 modules from the same source tarball as python2 modules
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|py_byte_compile|| (script) ||Defined in python3-devel.  See the [[Packaging:Python_Appendix#Manual_byte_compilation|byte compiling]] section for usage
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|-
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|python3_version|| 3.X ||Defined in python3-devel.  Useful when running programs with Python version in filename, such as nosetest-%{python3_version}
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|-
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|python3_version_nodots|| 3X ||Defined in python3-devel since Fedora 21 / Python 3.4.  Useful when listing files explicitly in %files section , such as %{python3_sitelib}/foo/*.cpython-%{python3_version_nodots}.pyo
 
|-
 
|-
|py_byte_compile|| (script) ||Defined in python3-devel.  See the [#Bytecompiling_with_the_correct_python_version bytecompiling] section for usage
 
 
|}
 
|}
  
During <code>%install</code> or when listing <code>%files</code> you can use the <code>python_sitearch</code> and <code>python_sitelib</code> macros to specify where the installed modules are to be found. For instance:
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{{admon/note|The generic %{_python} macros|
 
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The unversioned macros, <code>%{__python}</code>, <code>%{python_sitelib}</code>, and <code>%{python_sitearch}</code> are generic macros that will always point to the default implementation.  You may only use them with applications that need to choose to use the system's default version of python.  (Currently this is the python2 interpreter.)
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This is future proofing for the time when things will be switched over to python3 by default instead of python2.
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You should use <code>%{__python2}</code>, <code>%{python2_sitelib}</code>, and <code>%{python2_sitearch}</code> to explicitly reference the python2 interpreter instead.
 +
}}
  
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During <code>%install</code> or when listing <code>%files</code> you can use the <code>python2_sitearch</code> and <code>python2_sitelib</code> macros to specify where the installed modules are to be found.  For instance:
  
 
<pre>
 
<pre>
 
%files
 
%files
 
# A pure python2 module
 
# A pure python2 module
%{python_sitelib}/foomodule/
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%{python2_sitelib}/foomodule/
 
# A compiled python2 extension module
 
# A compiled python2 extension module
%{python_sitearch}/barmodule/
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%{python2_sitearch}/barmodule/
 
# A compiled python3 extension module
 
# A compiled python3 extension module
 
%{python3_sitearch}/bazmodule/
 
%{python3_sitearch}/bazmodule/
 
</pre>
 
</pre>
  
Using the macros has several benefits.
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Use of the macros has several benefits:
<ol>
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* It ensures that the packages are installed correctly on multilib architectures.
<li>It ensures that the packages are installed correctly on multilib architectures.</li>
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* Using these macros instead of hardcoding the directory in the specfile ensures your spec remains compatible with the installed python version even if the directory structure changes radically (for instance, if <code>python2_sitelib</code> moves into <code>%{_datadir}</code>).
<li>Using these macros instead of hardcoding the directory in the specfile ensures your spec remains compatible with the installed python version even if the directory structure changes radically (for instance, if <code>python_sitelib</code> moves into <code>%{_datadir}</code>)</li>
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</ol>
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== Files to include ==
 
== Files to include ==
When installing python modules we include several different types of files.
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When packaging python modules, several types of files are included:
<ul>
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* *.py source files because they are used when generating tracebacks.
<li>*.py source files because they are used when generating tracebacks</li>
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* *.pyc and *.pyo byte compiled files (and, if present, the enclosing __pycache__ directory in most cases).
<li>*.pyc and *.pyo byte compiled files
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** Python will try to create them at runtime if they don't exist which leads to spurious SELinux AVC denials in the logs.
<ul><li>python will try to create them at runtime if they don't exist which leads to spurious SELinux AVC denials in the logs</li>
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** If the system administrator invokes python with -OO, .pyos will be created with no docstrings.  This can break some programs.
<li>If the system administrator invokes python with -OO, .pyos will be created with no docstrings.  This can break some programs.</li>
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* *.egg-info files or directories.  If these are generated by the module's build scripts they must be included in the package because they might be needed by other applications and modules at runtime.
</ul>
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<li>*.egg-info files or directories.  If these are generated by the module's build scripts they must be included in the package because they might be needed by other applications and modules at runtime.</li>
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</ul>
+
  
== Source files ==
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The source files must be included in the same package as the byte compiled versions.
 
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Source files (*.py) must be included in the same packages as the byte-compiled
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versions of them.
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== Byte compiling ==
 
== Byte compiling ==
  
Python will automatically try to byte compile files when it runs in order to speed up startup the next time it is run.  These files are saved in files with the extension of .pyc (compiled python) or .pyo (optimized compiled python). These files are a byte code that is portable across OSes.  If you do not include them in your packages, python will try to create them when the user runs the program.  If the system administrator uses them, then the files will be successfully written.  Later, when the package is removed, the .pyc and .pyo files will be left behind on the filesystem.  To prevent that the byte compiled files need to be compiled and included in the <code>%files</code> sectionNormally, byte compilation is done for you by the <code>brp-python-bytecompile</code> script. This script runs after the <code>%install</code> section of the spec file has been processed and byte compiles any .py files that it finds (this recompilation puts the proper filesystem paths into the modules otherwise tracebacks would include the <code>%{buildroot}</code> in them). All that you need to do is include the files in the <code>%files</code> section.  The following are all acceptable ways to accomplish this:
+
Python will automatically try to byte compile files when it runs in order to speed up startup the next time it is run.  These files are saved in files with the extension of .pyc (compiled python) or .pyo (optimized compiled python). With current versions of python 3, these files will be located inside a directory named <code>__pycache__</code>.  Older versions of python will simply place them alongside the .py files.
  
<pre>
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The .pyc and .pyo files contain byte code that is portable across OSes.  If you do not include them in your packages, python will try (and generally fail) to create them when the user runs the program.  If the system administrator runs the program, then the files will be successfully written, causing stray .pyc and .pyo files which will not be removed when the package is removed.  To prevent that the byte compiled files need to be compiled and included in the <code>%files</code> section.  Normally, byte compilation is done for you by the <code>brp-python-bytecompile</code> script. This script runs after the <code>%install</code> section of the spec file has been processed and byte compiles any .py files that it finds (this recompilation puts the proper filesystem paths into the modules otherwise tracebacks would include the <code>%{buildroot}</code> in them).
%install
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install -d $RPM_BUILD_ROOT%{python_sitelib}/foo
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install -pm 0644 foo.py $RPM_BUILD_ROOT%{python_sitelib}/foo/
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Either:
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You must include in your package the .pyc and .pyo files.  If the build process creates a __pycache__ directory in a subdirectory of  %{python3_sitearch} or %{python3_sitelib}, you must also include all items in the __pycache__ directory.  (You should not include the directories %{python3_sitearch}/__pycache__ or %{python3_sitelib}/__pycache__ because they are already owned by the python3-libs package.)
  
%files
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All that you need to do is include the files in the <code>%files</code> section (replacing %{python3_sitelib} with the appropriate macro for your package):
%{python_sitelib}/foo/
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+
Or:
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%files
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%dir %{python_sitelib}/foo
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%{python_sitelib}/foo/*
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Or even:
+
  
 +
<pre>
 
%files
 
%files
%dir %{python_sitelib}/foo
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%{python3_sitelib}/foo/
%{python_sitelib}/foo/foo.py
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%{python_sitelib}/foo/foo.pyc
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%{python_sitelib}/foo/foo.pyo
+
 
</pre>
 
</pre>
  
{{admon/warning|Avoid INSTALLED_FILES|python's distutils has an <code>INSTALLED_FILES</code> feature that lists which files are installed when you run <code>python setup.py install</code>.  Do not use it for packaging as that will not list the directories which need to be specified in the <code>%files</code> section as well. Using globs in the <code>%files</code> section is simpler and safer.}}
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or, if the python code installs directly into %{python3_sitelib}:
 
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{{admon/warning|Including egg info|When you run <code>%{__python} setup.py install</code> in any current Fedora, distutils generates a <code>.egg-info</code> file with metadata about the python module that is installed.  These files need to be included as well. (See [https://fedoraproject.org/wiki/Packaging:Python#Packaging_eggs_and_setuptools_concerns Packaging eggs and setuptools concerns] )}}
+
 
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=== Bytecompiling with the correct python version ===
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When byte compiling a .py file, python embeds a magic number in the byte compiled files that correspond to the runtime.  Files in <code>%{python_sitelib}</code> and <code>%{python_sitearch}</code> must correspond to the runtime for which they were built.  For instance, a pure python module compiled for the 3.1 runtime needs to be below <code>%{_usr}/lib/python3.1/site-packages</code>
+
 
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The <code>brp-python-bytecompile</code> script tries to figure this out for you.  The script determines which interpreter to use when byte compiling the module by following these steps:
+
 
+
<ol>
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<li>what directory is the module installed in?  If it's <code>/usr/lib{,64}/pythonX.Y</code>, then <code>pythonX.Y</code> is used to byte compile the module.  If <code>pythonX.Y</code> is not installed, then an error is returned and the rpm build process will exit on an error so remember to <code>BuildRequire</code> the proper python package.</li>
+
 
+
<li>the script interpreter defined in <code>%{__python}</code> is used to compile the modules.  This defaults to the latest python2 version on Fedora.  If you need to compile this module for python3, set it to <code>/usr/bin/python3</code> instead:
+
  
 
<pre>
 
<pre>
%global __python %{__python3}
+
%files
 +
%{python3_sitelib}/foo.py
 +
%{python3_sitelib}/__pycache__/*
 
</pre>
 
</pre>
  
Doing this is useful when you have a python3 application that's installing a private module into its own directory.  For instance, if the foobar application installs a module for use only by the command line application in <code>%{_datadir}/foobar</code>.  Since these files are not in one of the python3 library paths (ie. <code>/usr/lib/python3.1</code>) you have to override <code>%{__python}</code> to tell <code>brp-python-bytecompile</code> to use the python3 interpreter for byte compiling.
+
{{admon/warning|Avoid INSTALLED_FILES|python's distutils has an <code>INSTALLED_FILES</code> feature that lists which files are installed when you run <code>%py_install</code>.  Do not use it for packaging as that will not list the directories which need to be specified in the <code>%files</code> section as well. Using globs in the <code>%files</code> section is simpler and safer.}}
</li>
+
</ol>
+
  
These settings are enough to properly byte compile any package that builds python modules in <code>%{python_sitelib}</code> or <code>%{python_sitearch}</code> or builds for only a single python interpreterHowever, if the application you're packaging needs to build with both python2 and python3 and install into a private module directory (perhaps because it provides one utility written in python2 and a second utility written in python3) then you need to do this manually. Here's a sample spec file snippet that shows what to do:
+
{{admon/warning|Including egg info|When you run <code>%py_install</code> in any current Fedora, distutils generates a <code>.egg-info</code> file with metadata about the python module that is installedThese files need to be included as well. (See [[#Packaging_eggs_and_setuptools_concerns|Packaging:Python_Eggs]] )}}
 
+
<pre>
+
# Turn off the brp-python-bytecompile script
+
%global __os_install_post %(echo '%{__os_install_post}' | sed -e 's!/usr/lib[^[:space:]]*/brp-python-bytecompile[[:space:]].*$!!g')
+
# Buildrequire both python2 and python3
+
BuildRequires: python2-devel python3-devel
+
[...]
+
 
+
%install
+
# Installs a python2 private module into %{buildroot}%{_datadir}/mypackage/foo
+
# and installs a python3 private module into %{buildroot}%{_datadir}/mypackage/bar
+
make install DESTDIR=%{buildroot}
+
 
+
# Manually invoke the python byte compile macro for each path that needs byte
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# compilation.
+
%py_byte_compile %{__python} %{buildroot}%{_datadir}/mypackage/foo
+
%py_byte_compile %{__python3} %{buildroot}%{_datadir}/mypackage/bar
+
</pre>
+
  
The <code>%py_byte_compile</code> macro takes two arguments.  The first is the python interpreter to use for byte compiling.  The second is a file or directory to byte compile.  If the second argument is a directory, the macro will recursively byte compile any *.py file in the directory.
+
=== Optimization ===
  
{{admon/warning|No %{} for py_byte_compile|RPM macros can only take arguments when they do not have curly braces around themTherefore, py_byte_compile won't work correctly if you write: <code>%{py_byte_compile} %{__python}</code>}}
+
Fedora packages running with python < 3.5 (including any version of python 2) '''must not''' invoke python with the <code>-OO</code> option or set the environment variable <code>PYTHONOPTIMIZE</code> to 2 or greater(Using -O or <code>PYTHONOPTIMIZE</code> less than 2 is fine, though unnecessary.)
  
 +
Similarly, any <code>.pyo</code> shipped in a Fedora package for python < 3.5 '''must not''' have been byte compiled using optimization level 2 or higher.
  
 +
=== Manual byte compilation ===
 +
For more details on the internals of byte compilation, please see [[Packaging:Python_Appendix#Manual_byte_compilation|the appendix]].
  
 
== Common SRPM vs split SRPMs ==
 
== Common SRPM vs split SRPMs ==
  
Many times when you package a python module you will want to create a module for python2 and a module for python3.  There are two ways of doing this: either from a single SRPM or from multipleThe rule to choose which method is simple: if the python2 and python3 modules are distributed as a single tarball (many times as a single directory of source where the <code>/usr/bin/2to3</code> program is used to transform the code at buildtime) then you must package them as subpackages built from a single SRPM.  If they come in multiple tarballs then package them from multiple SRPMs.
+
Many times when you package a python module you will want to create a module for python2 and a module for python3.  Both versions should be built from the same SRPM.  An exception to this would be if the two versions are distributed as separate archives and do not follow the same release schedule.
  
{{admon/note|Python Bindings|python bindings are sometimes built as part of the C library's build.  The ideal for these is to patch the code so it will build against both python2 and python3.  Then take a copy of the sources during the <code>%prep</code> phase, and configure one subdirectory to build against python 2, another to build against python 3.  These changes should be upstreamed.  Example: the build of <code>rpm</code> itself emits an <code>rpm-python</code> subpackage (see [[rhbug:531543|Red Hat Bug 531543]].)}}
+
{{admon/warning|Use of the <code>%python_provide</code> macro|When building more than once from the same spec file, you must not have a <code>%files</code> section. Instead you must build one subpackage for each python runtime and use the <code>%python_provide</code> macro as shown in the example specfile below.}}
  
=== Multiple SRPMS ===
+
== Example common spec file ==
  
When upstream ships multiple tarballs with one tarball containing python2 code and a different tarball containing python3 code, we should ship those as multiple SRPMsThe two SRPMs could have different maintainers within Fedora and the two packages need not upgrade at the same time. Building from multiple SRPMs has some advantages and disadvantages:
+
The following is a very simple spec file for a module building for both python2
 +
and python3.  It builds both versions in the same directory; this is possible
 +
because the build products for different versions of Python usually do not conflict.
  
'''Advantages''':
+
There are cases where it is not possible to build in a single directory.  Most
* There can be separate maintainers for python2 and python3 so each maintainer can concentrate on one stack.
+
commonly this happens when the sources are modified during the build process to
* The two packages can evolve separately; if 2 and 3 need to have different versions, they can.
+
convert them from python2 to python3 using the the <code>2to3</code> tool. In
 +
that case, please see [[Packaging:Python_Appendix#Using_separate_build_directories|the appendix]].
  
'''Disadvantages''':
+
As you can see in the <code>%install</code> section below, the order in which
* The two specfiles have to be maintained separately
+
you do the python2 versus python3 install can sometimes matterYou need to be
* When upstream releases e.g. security fixes, they have to be tracked in two places
+
aware of when the install is writing to the same file in both packages (in this
 
+
example, a script in <code>%{_bindir}</code> and make sure that you're getting
The following practices are designed to help mitigate the disadvantages listed above:
+
the version you expect.
 
+
* When packaging a module for python3 contact the maintainers for the python2 module and try to coordinate with them.
+
* Request at least watchbugzilla and watchcommit acls on each other's packages so you're aware of outstanding bugs.
+
* Complete any python 2 Merge Review when doing the python 3 version.  Doing this gets issues that apply to both packages addressed at the same time.
+
* Add a link to the python 2 Merge Review/Package Review to the python 3 Package Review
+
 
+
=== Subpackages ===
+
 
+
{{admon/warning|Do not build python3 modules without upstream support|If upstream is shipping a module for python2 and does not support making that module run on python3, do not package a python3 version of it in Fedora.  If running <code>2to3</code> or adding a patch enables the code to work, you can certainly tell upstream that it works to encourage them to support python3.  However, doing this on our own in Fedora is essentially creating a fork.  That has a large burden for maintaining the code, fixing bugs, porting when a new version of upstream's code appears, managing a release schedule, and other tasks normally handled by upstream.  It's much better if we can cooperate with upstream to share this work than doing it all on our own.}}
+
 
+
Sometimes upstream will ship one tarball that builds both a python2 and a python3 module.  There's several ways that upstream can structure thisWhen upstream writes their build scripts to build both python2 and python3 modules in a single build this is just like building subpackages for any other package.  You expand the tarball and patch the source in <code>%prep</code>, run upstream's build scripts to build the package in <code>%build</code>, and then run upstream's build scripts to install it in <code>%install</code>.
+
 
+
'''Advantages''':
+
* Single src.rpm to review and build
+
* Avoids having to update multiple packages when things change.
+
 
+
'''Disadvantages''':
+
* The Fedora maintainer needs to care about both python 2 and python 3 modules which makes more work to maintain that package.
+
* The 2 and 3 versions are in lockstep.  Bugfixes need to apply to python2 while not breaking the translation into python3.
+
* Bugzilla components are set up according to source RPM, so they will have a single shared bugzilla component.  This could be confusing to end-users, as it would be more difficult to figure out e.g. that a bug with python3-foo needs to be filed against python-foo.  There's a similar problem with checking out package sources from CVS, though this is less serious as it is less visible to end users.
+
 
+
Two other ways exist for the upstream to support building python3 modules from a single source:
+
 
+
==== Building more than once ====
+
 
+
One way that's currently very common is for the build scripts to create either a python2 or python3 module based on which interpreter is used to run the setup.py script.  (The [http://cvs.fedoraproject.org/viewvc/rpms/python-setuptools/devel/python-setuptools.spec?revision=1.31&view=markup python-setuptools package] is currently built this way).
+
 
+
===== Example spec file =====
+
  
 
<pre>
 
<pre>
%if 0%{?fedora} > 12
+
%global srcname example
%global with_python3 1
+
%global sum An example python module
%else
+
%{!?python_sitelib: %global python_sitelib %(%{__python} -c "from distutils.sysconfig import get_python_lib; print (get_python_lib())")}
+
%endif
+
  
%global srcname distribute
+
Name:          python-%{srcname}
</pre>
+
Version:        1.2.3
 +
Release:        1%{?dist}
 +
Summary:        %{sum}
  
At the top of our spec file we have the standard define for <code>python_sitelib</code> on older Fedora releases.  We also define <code>with_python3</code> which we'll use to conditionalize the build whenever we have a section that is only useful when building a python3 module.  Using <code>with_python3</code> allows us to do two things:
+
License:        MIT
 
+
URL:            https://pypi.python.org/pypi/%{srcname}
<ol>
+
Source0:        https://files.pythonhosted.org/packages/source/e/%{srcname}/%{srcname}-%{version}.tar.gz
<li>It makes it easy to turn off the python3 build when tracking down problems.</li>
+
<li>The conditionals also make it easy to use the same spec for older releases of Fedora and EPEL.</li>.
+
</ol>
+
 
+
{{admon/warning|Leave python3 module enabled in releases|Once python 3 support has been added to a package, you must leave it enabled.  End users could be using the python3 subpackage that is being built.  If you turn the subpackage build on and off it will cause the package to unexpectedly disappear from the repos.  You should only turn off <code>with_python3</code> as a debugging measure within scratch builds, for releases that do not support python 3, or when moving a python3 module into its own, independent package.}}
+
 
+
<pre>
+
Name:          python-setuptools
+
Version:        0.6.10
+
Release:        2%{?dist}
+
Summary:        Easily build and distribute Python packages
+
 
+
Group:          Applications/System
+
License:        Python or ZPLv2.0
+
URL:            http://pypi.python.org/pypi/%{srcname}
+
Source0:        http://pypi.python.org/packages/source/d/%{srcname}/%{srcname}-%{version}.tar.gz
+
# Fix a failing test case
+
Patch0:        python-setuptools-test.patch
+
BuildRoot:      %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
+
  
 
BuildArch:      noarch
 
BuildArch:      noarch
BuildRequires:  python2-devel
+
BuildRequires:  python2-devel python3-devel
%if 0%{?with_python3}
+
BuildRequires:  python3-devel
+
%endif # if with_python3
+
</pre>
+
  
When we build the python3 module in addition to the python3 module we need both <code>python2-devel</code> and <code>python3-devel</code>.
 
 
<pre>
 
 
%description
 
%description
Setuptools is a collection of enhancements to the Python distutils that allow
+
An python module which provides a convenient example.
you to more easily build and distribute Python packages, especially ones that
+
have dependencies on other packages.
+
  
This package contains the runtime components of setuptools, necessary to
+
%package -n python2-%{srcname}
execute the software that requires pkg_resources.py.
+
Summary:        %{sum}
 +
%{?python_provide:%python_provide python2-%{srcname}}
  
%if 0%{?with_python3}
+
%description -n python2-%{srcname}
%package -n python3-setuptools
+
An python module which provides a convenient example.
Summary:        Easily build and distribute Python 3 packages
+
Group:          Applications/System
+
  
%description -n python3-setuptools
 
Setuptools is a collection of enhancements to the Python 3 distutils that allow
 
you to more easily build and distribute Python 3 packages, especially ones that
 
have dependencies on other packages.
 
  
This package contains the runtime components of setuptools, necessary to
+
%package -n python3-%{srcname}
execute the software that requires pkg_resources.py.
+
Summary:        %{sum}
%endif # with_python3
+
%{?python_provide:%python_provide python3-%{srcname}}
</pre>
+
 
 +
%description -n python3-%{srcname}
 +
An python module which provides a convenient example.
  
Here we define the python3 subpackage.  Note that we use <code>%package -n</code> to name the module appropriately.
 
  
<pre>
 
 
%prep
 
%prep
%setup -q -n %{srcname}-%{version}
+
%autosetup -n %{srcname}-%{version}
  
%patch0 -p1 -b .testfix
 
 
find -name '*.txt' | xargs chmod -x
 
 
%if 0%{?with_python3}
 
rm -rf %{py3dir}
 
cp -a . %{py3dir}
 
find %{py3dir} -name '*.py' | xargs sed -i '1s|^#!python|#!%{__python3}|'
 
%endif # with_python3
 
 
find -name '*.py' | xargs sed -i '1s|^#!python|#!%{__python}|'
 
</pre>
 
 
 
Our method in building from the same code to make the two separate modules is to keep each build as independent as possible.  To do that, we copy the source tree to <code>%{py3dir}</code> so that the python 2 sources are entirely independent from the python 3 sources.  Some things to watch out for:
 
 
* Be sure to clean up the <code>%{py3dir}</code> before performing the copy.  It's easy to forget that since <code>%setup</code> does that automatically for the python2 module.
 
* Make sure that you are copying the correct code.  The example is copying the code from within the top directory of the untarred source.  If the <code>%prep</code> has changed directory you will need to change back to the tarball location.
 
* Patching the source code is done before copying to <code>%{py3dir}</code>.  Since you have both a python2 and a python3 directory you might be tempted to patch each one separately.  '''Resist!'''  Upstream for your package has chosen to distribute a single source tree that builds for both python2 and python3.  For your patches to [[Staying_close_to_upstream_projects| get into upstream]], you need to write patches that work with both as well.}}
 
 
<code>rpmbuild</code> resets the directory at the end of each phase, so you don't need to restore the directory at the end of <code>%prep</code>.
 
 
<pre>
 
 
%build
 
%build
CFLAGS="$RPM_OPT_FLAGS" %{__python} setup.py build
+
%py2_build
 
+
%py3_build
%if 0%{?with_python3}
+
pushd %{py3dir}
+
CFLAGS="$RPM_OPT_FLAGS" %{__python3} setup.py build
+
popd
+
%endif # with_python3
+
  
 
%install
 
%install
rm -rf %{buildroot}
+
# Must do the python2 install first because the scripts in /usr/bin are
 
+
# overwritten with every setup.py install, and in general we want the
# Must do the python3 install first because the scripts in /usr/bin are
+
# python3 version to be the default.
# overwritten with every setup.py install (and we want the python2 version
+
%py2_install
# to be the default for now).
+
%py3_install
%if 0%{?with_python3}
+
pushd %{py3dir}
+
%{__python3} setup.py install --skip-build --root $RPM_BUILD_ROOT
+
 
+
rm -rf %{buildroot}%{python3_sitelib}/setuptools/tests
+
 
+
find %{buildroot}%{python3_sitelib} -name '*.exe' | xargs rm -f
+
chmod +x %{buildroot}%{python3_sitelib}/setuptools/command/easy_install.py
+
popd
+
%endif # with_python3
+
 
+
%{__python} setup.py install --skip-build --root $RPM_BUILD_ROOT
+
 
+
rm -rf ${buildroot}%{python_sitelib}/setuptools/tests
+
 
+
find %{buildroot}%{python_sitelib} -name '*.exe' | xargs rm -f
+
chmod +x %{buildroot}%{python_sitelib}/setuptools/command/easy_install.py
+
  
 
%check
 
%check
%{__python} setup.py test
+
%{__python2} setup.py test
 
+
%if 0%{?with_python3}
+
pushd %{py3dir}
+
 
%{__python3} setup.py test
 
%{__python3} setup.py test
popd
 
%endif # with_python3
 
</pre>
 
  
You'll notice that the <code>%build</code>, <code>%install</code>, and <code>%check</code> sections follow a common pattern.  They do the normal steps for building the python2 module but then they switch to <code>%{py3dir}</code> and run the same steps for python3. Creating the new sections is generally pretty easy.  First copy the existing code.  Then wrap it with a <code>pushd/popd</code> to <code>%{py3dir}</code>.  The usage of <code>pushd/popd</code> commands will ensure that the directories are logged. Finally, convert all macro references:
+
# Note that there is no %%files section for the unversioned python module if we are building for several python runtimes
 +
%files -n python2-%{srcname}
 +
%license COPYING
 +
%doc README.rst
 +
%{python2_sitelib}/*
 +
%{_bindir}/sample-exec-2.7
  
* <code>%{__python}</code> becomes <code>%{__python3}</code>
+
%files -n python3-%{srcname}
* <code>%{python_sitelib}</code> becomes <code>%{python3_sitelib}</code>
+
%license COPYING
* <code>%{python_sitearch}</code> becomes <code>%{python3_sitearch}</code>
+
%doc README.rst
 
+
{{admon/warning|Order can be important|As you can see in the <code>%install</code> section, the order in which you do the python2 versus python3 install can sometimes matter.  You need to be aware of when the install is writing to the same file in both packages (in this example, a script in <code>%{_bindir}</code> and make sure that you're getting the version you expect.}}
+
 
+
<pre>
+
%clean
+
rm -rf $RPM_BUILD_ROOT
+
 
+
 
+
%files
+
%doc psfl.txt zpl.txt docs
+
%{python_sitelib}/*
+
%{_bindir}/easy_install
+
%{_bindir}/easy_install-2.6
+
 
+
%if 0%{?with_python3}
+
%files -n python3-setuptools
+
%doc psfl.txt zpl.txt docs
+
 
%{python3_sitelib}/*
 
%{python3_sitelib}/*
%{_bindir}/easy_install-3.1
+
%{_bindir}/sample-exec
%endif # with_python3
+
%{_bindir}/sample-exec-3.4
  
 
%changelog
 
%changelog
 
</pre>
 
</pre>
 
In this final section, you can see that we once again switch macros from <code>%{python_sitelib}</code> to <code>%{python3_sitelib}</code>.  Since we chose to install the python2 version of <code>%{_bindir}/easy_install</code> earlier we need to include that file in the python2 package rather than the python3 subpackage.
 
 
==== Running 2to3 from the spec file ====
 
Sometimes, upstream hasn't integrated running 2to3 on the code into their build scripts but they support making a python3 module from it if you manually run 2to3 on the source.  This is the case when it's documented on the upstream's website, in a file in the tarball, or even when email with the module's author has instructions for building a python3 module from the python2 source and the authors are willing to support the result.  In these cases it's usually just a matter of the upstream not having written the build script that can turn the python2 source into python3.  When this happens you can run <code>2to3</code> from the spec file.  Once you have it working, you can also help upstream integrate it into their build scripts which will benefit everyone in the long term.
 
 
You should usually follow upstream's directions on how to run <code>2to3</code> and build the python3 module in these cases but there's a few things you should check to make sure upstream is doing it correctly.
 
 
* Since the code is being built from a unified source, you need to copy the code to a new directory before invoking 2to3 just like the [[#Building_more_than_once| building more than once]] method.
 
* If the <code>2to3</code> program is invoked instead of using the <code>lib2to3</code> library functions, make sure it's invoked with <code>--write --nobackups</code>.  <code>--write</code> is needed to make <code>2to3</code> actually change the files.  <code>--nobackups</code> avoids leaving <code>foo.py.bak</code> files in the module directories that then make it into the final package payload.
 
* Be sure to run 2to3 on the correct directory.  When you run <code>2to3</code> you need to run it on the whole tree.  A common mistake here for distutils packages has been to run it on the directory below <code>setup.py</code>, missing the <code>setup.py</code> file itself.  This leads to errors when <code>python3</code> tries to execute <code>setup.py</code>
 
* If you need to run <code>2to3</code> to fix code, use <code>2to3</code> or <code>/usr/bin/2to3</code>.  At the moment, this program is coming from the <code>python-tools</code> rpm.  Using <code>2to3</code> means that you'll be using a name that is supported upstream and across distros rather than <code>/usr/bin/python3-2to3</code> which we have renamed in Fedora to avoid filesystem conflicts.  This also makes it easier for us to test and eventually change from using the python2 <code>2to3</code> to the python3 <code>2to3</code>.  We just need to change the python3 package to provide the <code>/usr/bin/2to3</code> program instead of python and all of our python packages will start using that version instead.
 
* If <code>2to3</code> runs into a problem, please [https://bugzilla.redhat.com/enter_bug.cgi?component=python&product=Fedora file a Fedora bug].  Please try to isolate a minimal test case that reproduces the problem when doing so.
 
  
 
== Avoiding collisions between the python 2 and python 3 stacks ==
 
== Avoiding collisions between the python 2 and python 3 stacks ==
Line 409: Line 236:
  
 
=== Executables in <code>/usr/bin</code> ===
 
=== Executables in <code>/usr/bin</code> ===
==== The problem ====
+
Many existing python packages install executables into <code>/usr/bin</code>.
Many existing python packages install executables into <code>/usr/bin</code>.  
+
  
 
For example if we have a <code>console_scripts</code> in a <code>setup.py</code> shared between
 
For example if we have a <code>console_scripts</code> in a <code>setup.py</code> shared between
Line 436: Line 262:
 
which generates a <code>/usr/bin/pygmentize</code> (this is a python script that leverages the pygments syntax-highlighting module, giving a simple command-line interface for generating syntax-highlighted files)
 
which generates a <code>/usr/bin/pygmentize</code> (this is a python script that leverages the pygments syntax-highlighting module, giving a simple command-line interface for generating syntax-highlighted files)
  
==== Guidelines ====
+
If the executables provide the same functionality independent of whether they are run on top of Python 2 or Python 3, then only the Python 3 version of the executable should be packaged.  Transitioning from python2 to python3 is left to individual package maintainers except for packages in Fedora's critical path.  For these, we want to port to python3 versions in the same Fedora release if possible.
If the executables provide the same functionality independent of whether they are run on top of Python 2 or Python 3, then only one version of the executable should be packaged.  Currently it will be the python 2 implementation, but once the Python 3 implementation is proven to work, the executable can be retired from the python 2 build and enabled in the python 3 package.  Be sure to test the new implementation.  Transitioning from python2 to python3 is left to individual package maintainers except for packages in Fedora's critical path.  For these, we want to port to python3 versions in the same Fedora release if possible.
+
  
 
Examples of this:
 
Examples of this:
 
* <code>/usr/bin/pygmentize</code> ought to generate the same output regardless of whether it's implemented via Python 2 or Python 3, so only one version needs to be shipped.
 
* <code>/usr/bin/pygmentize</code> ought to generate the same output regardless of whether it's implemented via Python 2 or Python 3, so only one version needs to be shipped.
  
If the executables provide different functionality for Python 2 and Python 3, then both versions should be packaged.  
+
If the executables provide different functionality for Python 2 and Python 3, then both versions should be packaged.
  
 
Examples of this:
 
Examples of this:
Line 448: Line 273:
 
* <code>/usr/bin/bpython</code> augments the interpreter with a "curses" interface.  Again, it's reasonable to package both versions of this.
 
* <code>/usr/bin/bpython</code> augments the interpreter with a "curses" interface.  Again, it's reasonable to package both versions of this.
 
* <code>/usr/bin/easy_install</code> installs a module into one of the Python runtimes: we need a version for each runtime.
 
* <code>/usr/bin/easy_install</code> installs a module into one of the Python runtimes: we need a version for each runtime.
 
 
As an exception, for the rpms that are part of a python runtime itself, we plan to package both versions of the executables, so that e.g. both the python 2 and python 3 versions of <code>2to3</code> are packaged.
 
  
==== Naming ====
+
As an exception, for the packages that are part of a python runtime itself, we plan to package both versions of the executables, so that e.g. both the python 2 and python 3 versions of <code>2to3</code> are packaged.
Many executables already contain a "-MAJOR.MINOR" suffix, for example <code>/usr/bin/easy_install-3.1</code>.  These obviously can be used as-is, as they won't conflict.
+
 
 +
=== Naming ===
 +
Many executables already contain a "-MAJOR.MINOR" suffix, for example <code>/usr/bin/easy_install-3.4</code>.  These obviously can be used as-is, as they won't conflict.
  
 
For other executables, the general rule is:
 
For other executables, the general rule is:
* if only one executable is to be shipped, then it owns its own slot
+
* If only one executable is to be shipped, then it owns its own slot and should use /usr/bin/python3 from Fedora 22 on.
* if executables are to be shipped for both python 2 and python 3, then the python 3 version of the executable gains a <code>python3-</code> prefix. For example, the python 2 version of "coverage" remains <code>/usr/bin/coverage</code> and the python 3 version is <code>/usr/bin/python3-coverage</code>.
+
* If executables are to be shipped for both python 2 and python 3:
See [http://lists.fedoraproject.org/pipermail/devel/2010-January/129217.html this thread] for a discussion of this.
+
** Both python 2 and python 3 variants must provide symlinks with a '-X' and '-X.Y' suffix (python runtime major version, or python runtime major.minor version), unless upstream already provides appropriately versioned executables without the dash.
 +
** The unversioned executable '''must''' be the python2 version.
 +
** For example, the python3 version of "coverage" '''must''' ship executables <code>/usr/bin/coverage-3</code> and <code>/usr/bin/coverage-3.4</code> (assuming python3 is currently version 3.4), while the python2 version '''must''' provide <code>/usr/bin/coverage</code>, <code>/usr/bin/coverage-2</code> and <code>/usr/bin/coverage-2.7</code> (assuming python2 version 2.7).
 +
** For compatibility packages, the Python version is appended *after* the specific package version, for example <code>/usr/bin/coverage-v1.2-3</code> and <code>/usr/bin/coverage-v1.2-3.4</code> for python3-coverage1.2 compat package.
 +
See [http://lists.fedoraproject.org/pipermail/devel/2010-January/129217.html this thread] and a newer thread [https://lists.fedoraproject.org/pipermail/packaging/2014-December/010360.html] for discussions of this.
  
== Packaging eggs and setuptools concerns ==
+
== Packaging eggs ==
 +
Please see the Python eggs [[Packaging:Python_Eggs|guidelines]] for information specific to Python eggs.
  
Eggs can mean several different things because they can be placed on disk in several formats:
+
== Reviewer checklist ==
 
+
The following briefly summarizes the guidelines for reviewers to go over:
* A module and a file with a .egg-info extension that contains the metadata.  Created by distutils in Fedora 9 and above.
+
* '''Must''': If you build for more than one python runtime you must use the <code>%python_provide</code> macro.
* As a module and a directory with a .egg-info extension that contains the metadata.  Created using setuptools and also the invocation of setup.py in our examples below.
+
* '''Must''': If you build for a single python runtime you must add <code>%python_provide python-$module</code> so that the current default python is provided from the unversioned python package.
* As a directory with a .egg extension that contains the module and egg metadata.  Created when we use easy_install -m to allow installing multiple versions of a module.
+
* '''Must''': Python modules must be built from source.  They cannot simply drop an egg from upstream into the proper directory. (See [[Packaging:Guidelines#No_inclusion_of_pre-built_binaries_or_libraries| prebuilt binaries Guidelines]] for details)
* As a single zip file with a .egg extension that contains the module and the egg metadata.
+
* '''Must''': Python modules must not download any dependencies during the build process.
 
+
In Fedora packages, these will be installed to %{python_sitelib} or %{python_sitearch} directories.  We do not install the single zip file version of eggs in Fedora but the three other formats are used.
+
 
+
=== How to package ===
+
 
+
The following are a summary of the guidelines for reviewers to go over when a python module is packaged. The [[Packaging:Python Eggs|  complete policy]]  includes examples and rationale for the way we do things.
+
 
+
* '''Must''': Python eggs must be built from source.  They cannot simply drop an egg from upstream into the proper directory. (See [[Packaging:Guidelines#No_inclusion_of_pre-built_binaries_or_libraries| prebuilt binaries Guidelines]] for details)
+
* '''Must''': Python eggs must not download any dependencies during the build process.
+
 
* '''Must''': When building a compat package, it must install using easy_install -m so it won't conflict with the main package.
 
* '''Must''': When building a compat package, it must install using easy_install -m so it won't conflict with the main package.
 
* '''Must''': When building multiple versions (for a compat package) one of the packages must contain a default version that is usable via "import MODULE" with no prior setup.
 
* '''Must''': When building multiple versions (for a compat package) one of the packages must contain a default version that is usable via "import MODULE" with no prior setup.
Line 483: Line 304:
 
RPM's dependency generator can often throw in additional dependencies and will often think packages provide functionality contrary to reality. To fix this, the dependency generator needs to be overriden so that the additional dependencies can be filtered out.  See [[Packaging:AutoProvidesAndRequiresFiltering]] for details.
 
RPM's dependency generator can often throw in additional dependencies and will often think packages provide functionality contrary to reality. To fix this, the dependency generator needs to be overriden so that the additional dependencies can be filtered out.  See [[Packaging:AutoProvidesAndRequiresFiltering]] for details.
  
== PyGTK2 and Numpy ==
+
[[Category:Packaging guidelines]]
{{admon/note||This is a temporary workaround which may be resolved in the future. It will no longer be necessary when [[http://bugzilla.gnome.org/show_bug.cgi?id=591745 gnome bug #591745]] is fixed.}}
+
[[Category:Python]]
 
+
If your package uses pygtk2, and calls the gtk.gdk.get_pixels_array() function, that package needs to explicitly Require: numpy. In the past, pygtk2 had a Requires on numpy, but since it is only used for that one function (and that function is not commonly used), the Requires has been removed to minimize the install footprint of pygtk2.
+
 
+
[[Category:Packaging guidelines]] [[Category:Python]]
+

Latest revision as of 14:54, 4 August 2016

[edit] Python Version Support

In Fedora we have multiple Python runtimes, one for each supported major Python release. At this point that's one for python2.x and one for python3.x. If a piece of software supports python3, it must be packaged for python3. If it supports python2 as well, it may be packaged for python2. If it supports only python2 then (obviously) it must not be packaged for python3.

[edit] Multiple Python Runtimes

Each runtime corresponds to a binary of the form /usr/bin/python$MAJOR.$MINOR. One of these python runtimes is the "system runtime" which is what is run when invoking /usr/bin/python. On Fedora 22, for example, this is a link to /usr/bin/python2 (which itself is a link to /usr/bin/python2.7).

However, packages in Fedora should not depend on where /usr/bin/python happens to point but instead should call the proper executable for the needed python major version directly, either /usr/bin/python2 or /usr/bin/python3 as appropriate.

All python runtimes have a virtual provide for python(abi) = $MAJOR-$MINOR. For example, the python-3.4 runtime rpm has:

 $ rpm -q --provides python3 |grep -i abi
 python(abi) = 3.4

python modules using these runtimes should have a corresponding "Requires" line on the python runtime that they are used with. This is done automatically for files below /usr/lib[^/]*/python${PYVER}

Mirroring policy for regular packages, the Python-version-specific subpackages of your package most not be removed in a release branch of Fedora.

[edit] BuildRequires

Packages building for python2 will need BuildRequires: python2-devel. Packages building for python3 will need BuildRequires: python3-devel. Packages building for for both will need build dependencies on both.

[edit] Provides

Using a fictional module named "example", the subpackage containing the python2 version must provide python2-example. This is of course always the case if the subpackage is named python2-example (as in the examples below). If the subpackage has some other name then then Provides: python2-example must be added explicitly (but see the %python_provide macro below).

The python3 subpackage must provide python3-example. However, as the naming guidelines mandate that the python3 subpackage be named python3-example, this will happen automatically.

[edit] The %python_provide macro

In addition, the subpackage corresponding to the current system runtime must provide Provides: python-example. However, the system version of python in Fedora will almost certainly change at some point in the future.

To avoid having to alter every python module package when this change happens, and to allow the same spec to build for releases with different system versions of python, a convenient %python_provide macro is provided. When given (as an argument) the name of the current subpackage, it will evaluate to either the proper Provide: line or nothing at all as appropriate for the version of the system runtime. Thus if the package follows the suggested subpackage naming scheme as shown in the below example, placing this macro in the definition of each subpackage will guarantee that the necessary Provide: line appears where it should, and does not appear where it shouldn't.

Finally, if the %python_provide is called with python-example (no python major version in the name) then it will evaluate to either Provides: python2-example or Provides: python3-example depending on the version of the current system runtime.

[edit] Macros

The following macros are defined for you:

Macro Normal Definition Notes
__python %{__python2} Default Python interpreter. Currently links to Python2 interpreter
__python2 /usr/bin/python2 Python 2 interpreter. Also the current default python interpreter
__python3 /usr/bin/python3 Python 3 interpreter
python_provide (Lua script) Given a package name, evaluates to either Provides: python-example or nothing at all depending on the version of the system runtime. See here for an example.
python_sitelib %{python2_sitelib} Where pure python modules are installed for the default Python implementation
python_sitearch %{python2_sitearch} Where python extension modules that are compiled C are installed for the default Python implementation
python2_sitelib /usr/lib/python2.X/site-packages Where pure python2 modules are installed
python2_sitearch /usr/lib64/python2.X/site-packages on x86_64
/usr/lib/python2.X/site-packages on x86
Where python2 extension modules that are compiled C are installed
python3_sitelib /usr/lib/python3.X/site-packages Where pure python3 modules are installed
python3_sitearch /usr/lib64/python3.X/site-packages on x86_64
/usr/lib/python3.X/site-packages on x86
Where python3 extension modules that are compiled C are installed
py_byte_compile (script) Defined in python3-devel. See the byte compiling section for usage
python3_version 3.X Defined in python3-devel. Useful when running programs with Python version in filename, such as nosetest-%{python3_version}
python3_version_nodots 3X Defined in python3-devel since Fedora 21 / Python 3.4. Useful when listing files explicitly in %files section , such as %{python3_sitelib}/foo/*.cpython-%{python3_version_nodots}.pyo
Note.png
The generic %{_python} macros
The unversioned macros, %{__python}, %{python_sitelib}, and %{python_sitearch} are generic macros that will always point to the default implementation. You may only use them with applications that need to choose to use the system's default version of python. (Currently this is the python2 interpreter.)

This is future proofing for the time when things will be switched over to python3 by default instead of python2.

You should use %{__python2}, %{python2_sitelib}, and %{python2_sitearch} to explicitly reference the python2 interpreter instead.

During %install or when listing %files you can use the python2_sitearch and python2_sitelib macros to specify where the installed modules are to be found. For instance:

%files
# A pure python2 module
%{python2_sitelib}/foomodule/
# A compiled python2 extension module
%{python2_sitearch}/barmodule/
# A compiled python3 extension module
%{python3_sitearch}/bazmodule/

Use of the macros has several benefits:

  • It ensures that the packages are installed correctly on multilib architectures.
  • Using these macros instead of hardcoding the directory in the specfile ensures your spec remains compatible with the installed python version even if the directory structure changes radically (for instance, if python2_sitelib moves into %{_datadir}).

[edit] Files to include

When packaging python modules, several types of files are included:

  • *.py source files because they are used when generating tracebacks.
  • *.pyc and *.pyo byte compiled files (and, if present, the enclosing __pycache__ directory in most cases).
    • Python will try to create them at runtime if they don't exist which leads to spurious SELinux AVC denials in the logs.
    • If the system administrator invokes python with -OO, .pyos will be created with no docstrings. This can break some programs.
  • *.egg-info files or directories. If these are generated by the module's build scripts they must be included in the package because they might be needed by other applications and modules at runtime.

The source files must be included in the same package as the byte compiled versions.

[edit] Byte compiling

Python will automatically try to byte compile files when it runs in order to speed up startup the next time it is run. These files are saved in files with the extension of .pyc (compiled python) or .pyo (optimized compiled python). With current versions of python 3, these files will be located inside a directory named __pycache__. Older versions of python will simply place them alongside the .py files.

The .pyc and .pyo files contain byte code that is portable across OSes. If you do not include them in your packages, python will try (and generally fail) to create them when the user runs the program. If the system administrator runs the program, then the files will be successfully written, causing stray .pyc and .pyo files which will not be removed when the package is removed. To prevent that the byte compiled files need to be compiled and included in the %files section. Normally, byte compilation is done for you by the brp-python-bytecompile script. This script runs after the %install section of the spec file has been processed and byte compiles any .py files that it finds (this recompilation puts the proper filesystem paths into the modules otherwise tracebacks would include the %{buildroot} in them).

You must include in your package the .pyc and .pyo files. If the build process creates a __pycache__ directory in a subdirectory of  %{python3_sitearch} or %{python3_sitelib}, you must also include all items in the __pycache__ directory. (You should not include the directories %{python3_sitearch}/__pycache__ or %{python3_sitelib}/__pycache__ because they are already owned by the python3-libs package.)

All that you need to do is include the files in the %files section (replacing %{python3_sitelib} with the appropriate macro for your package):

%files
%{python3_sitelib}/foo/

or, if the python code installs directly into %{python3_sitelib}:

%files
%{python3_sitelib}/foo.py
%{python3_sitelib}/__pycache__/*
Warning.png
Avoid INSTALLED_FILES
python's distutils has an INSTALLED_FILES feature that lists which files are installed when you run %py_install. Do not use it for packaging as that will not list the directories which need to be specified in the %files section as well. Using globs in the %files section is simpler and safer.
Warning.png
Including egg info
When you run %py_install in any current Fedora, distutils generates a .egg-info file with metadata about the python module that is installed. These files need to be included as well. (See Packaging:Python_Eggs )

[edit] Optimization

Fedora packages running with python < 3.5 (including any version of python 2) must not invoke python with the -OO option or set the environment variable PYTHONOPTIMIZE to 2 or greater. (Using -O or PYTHONOPTIMIZE less than 2 is fine, though unnecessary.)

Similarly, any .pyo shipped in a Fedora package for python < 3.5 must not have been byte compiled using optimization level 2 or higher.

[edit] Manual byte compilation

For more details on the internals of byte compilation, please see the appendix.

[edit] Common SRPM vs split SRPMs

Many times when you package a python module you will want to create a module for python2 and a module for python3. Both versions should be built from the same SRPM. An exception to this would be if the two versions are distributed as separate archives and do not follow the same release schedule.

Warning.png
Use of the %python_provide macro
When building more than once from the same spec file, you must not have a %files section. Instead you must build one subpackage for each python runtime and use the %python_provide macro as shown in the example specfile below.

[edit] Example common spec file

The following is a very simple spec file for a module building for both python2 and python3. It builds both versions in the same directory; this is possible because the build products for different versions of Python usually do not conflict.

There are cases where it is not possible to build in a single directory. Most commonly this happens when the sources are modified during the build process to convert them from python2 to python3 using the the 2to3 tool. In that case, please see the appendix.

As you can see in the %install section below, the order in which you do the python2 versus python3 install can sometimes matter. You need to be aware of when the install is writing to the same file in both packages (in this example, a script in %{_bindir} and make sure that you're getting the version you expect.

%global srcname example
%global sum An example python module

Name:           python-%{srcname}
Version:        1.2.3
Release:        1%{?dist}
Summary:        %{sum}

License:        MIT
URL:            https://pypi.python.org/pypi/%{srcname}
Source0:        https://files.pythonhosted.org/packages/source/e/%{srcname}/%{srcname}-%{version}.tar.gz

BuildArch:      noarch
BuildRequires:  python2-devel python3-devel

%description
An python module which provides a convenient example.

%package -n python2-%{srcname}
Summary:        %{sum}
%{?python_provide:%python_provide python2-%{srcname}}

%description -n python2-%{srcname}
An python module which provides a convenient example.


%package -n python3-%{srcname}
Summary:        %{sum}
%{?python_provide:%python_provide python3-%{srcname}}

%description -n python3-%{srcname}
An python module which provides a convenient example.


%prep
%autosetup -n %{srcname}-%{version}

%build
%py2_build
%py3_build

%install
# Must do the python2 install first because the scripts in /usr/bin are
# overwritten with every setup.py install, and in general we want the
# python3 version to be the default.
%py2_install
%py3_install

%check
%{__python2} setup.py test
%{__python3} setup.py test

# Note that there is no %%files section for the unversioned python module if we are building for several python runtimes
%files -n python2-%{srcname}
%license COPYING
%doc README.rst
%{python2_sitelib}/*
%{_bindir}/sample-exec-2.7

%files -n python3-%{srcname}
%license COPYING
%doc README.rst
%{python3_sitelib}/*
%{_bindir}/sample-exec
%{_bindir}/sample-exec-3.4

%changelog

[edit] Avoiding collisions between the python 2 and python 3 stacks

The python 2 and python 3 stacks are intended to be fully-installable in parallel. When generalizing the package for both python 2 and python 3, it is important to ensure that two different built packages do not attempt to place different payloads into the same path.

[edit] Executables in /usr/bin

Many existing python packages install executables into /usr/bin.

For example if we have a console_scripts in a setup.py shared between python 2 and python 3 builds: these will spit out files in /usr/bin/, and these will collide.

For example python-coverage has a setup.py that contains:

    entry_points = {
        'console_scripts': [
            'coverage = coverage:main',
            ]
        },

which thus generates a /usr/bin/coverage executable (this is a python script that runs another python script whilst generating code-coverage information on the latter).

Similarly for the 'scripts' clause; see e.g. python-pygments: Pygments-1.1.1/setup.py has:

    scripts = ['pygmentize'],

which generates a /usr/bin/pygmentize (this is a python script that leverages the pygments syntax-highlighting module, giving a simple command-line interface for generating syntax-highlighted files)

If the executables provide the same functionality independent of whether they are run on top of Python 2 or Python 3, then only the Python 3 version of the executable should be packaged. Transitioning from python2 to python3 is left to individual package maintainers except for packages in Fedora's critical path. For these, we want to port to python3 versions in the same Fedora release if possible.

Examples of this:

  • /usr/bin/pygmentize ought to generate the same output regardless of whether it's implemented via Python 2 or Python 3, so only one version needs to be shipped.

If the executables provide different functionality for Python 2 and Python 3, then both versions should be packaged.

Examples of this:

  • /usr/bin/coverage runs a python script, augmenting the interpreter with code-coverage information. Given that the interpreter itself is the thing being worked with, it's reasonable to package both versions of the executable.
  • /usr/bin/bpython augments the interpreter with a "curses" interface. Again, it's reasonable to package both versions of this.
  • /usr/bin/easy_install installs a module into one of the Python runtimes: we need a version for each runtime.

As an exception, for the packages that are part of a python runtime itself, we plan to package both versions of the executables, so that e.g. both the python 2 and python 3 versions of 2to3 are packaged.

[edit] Naming

Many executables already contain a "-MAJOR.MINOR" suffix, for example /usr/bin/easy_install-3.4. These obviously can be used as-is, as they won't conflict.

For other executables, the general rule is:

  • If only one executable is to be shipped, then it owns its own slot and should use /usr/bin/python3 from Fedora 22 on.
  • If executables are to be shipped for both python 2 and python 3:
    • Both python 2 and python 3 variants must provide symlinks with a '-X' and '-X.Y' suffix (python runtime major version, or python runtime major.minor version), unless upstream already provides appropriately versioned executables without the dash.
    • The unversioned executable must be the python2 version.
    • For example, the python3 version of "coverage" must ship executables /usr/bin/coverage-3 and /usr/bin/coverage-3.4 (assuming python3 is currently version 3.4), while the python2 version must provide /usr/bin/coverage, /usr/bin/coverage-2 and /usr/bin/coverage-2.7 (assuming python2 version 2.7).
    • For compatibility packages, the Python version is appended *after* the specific package version, for example /usr/bin/coverage-v1.2-3 and /usr/bin/coverage-v1.2-3.4 for python3-coverage1.2 compat package.

See this thread and a newer thread [1] for discussions of this.

[edit] Packaging eggs

Please see the Python eggs guidelines for information specific to Python eggs.

[edit] Reviewer checklist

The following briefly summarizes the guidelines for reviewers to go over:

  • Must: If you build for more than one python runtime you must use the %python_provide macro.
  • Must: If you build for a single python runtime you must add %python_provide python-$module so that the current default python is provided from the unversioned python package.
  • Must: Python modules must be built from source. They cannot simply drop an egg from upstream into the proper directory. (See prebuilt binaries Guidelines for details)
  • Must: Python modules must not download any dependencies during the build process.
  • Must: When building a compat package, it must install using easy_install -m so it won't conflict with the main package.
  • Must: When building multiple versions (for a compat package) one of the packages must contain a default version that is usable via "import MODULE" with no prior setup.
  • Should: A package which is used by another package via an egg interface should provide egg info.

[edit] Filtering Requires: and Provides:

RPM's dependency generator can often throw in additional dependencies and will often think packages provide functionality contrary to reality. To fix this, the dependency generator needs to be overriden so that the additional dependencies can be filtered out. See Packaging:AutoProvidesAndRequiresFiltering for details.