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Porting applications that happen to be written in Python

Porting the specfile to Python 3

Applications behave the same when run under Python 2 and Python 3, therefore all you need to do is change the spec file to use Python 3 instead of Python 2.

In essence, porting of an application RPM mostly consists of going through the spec file and adding number 3 or substituting number 3 for number 2 where appropriate. Occasionally also substituting old macros for new ones that are more versatile.

So let's take an example spec file and port it to illustrate the process. We start with a spec file for an application that is being run with Python 2:

.. literalinclude:: specs/application.spec.orig
   :language: spec

BuildRequires and Requires

Change BuildRequires from python-devel to python3-devel and adjust all other Requires and BuildRequires entries to point only to python3 packages.

It is very important that you don't use any Python 2 dependencies as that would make your package depend both on Python version 2 and version 3, which would render your porting efforts useless.

%build

In the build section you can find a variety of macros, for example %py_build and its newer version %py2_build. You can freely substitute these by the new Python 3 macro %py3_build.

Occasionally you will find a custom build command prefixed by the %{__python} or %{__python2} macros, or in some cases just prefixed by the Python interpreter invoked without a macro at all, e.g.:

%{__python} setup.py build
    or
python setup.py build

In these cases first try substituting the whole build command by the new smart macro %py3_build which should in many cases correctly figure out what ought to be done automatically. Otherwise change the invocation of the Python interpreter to the %{__python3} macro.

In rare cases, you might encounter some non-Python build script such as a Makefile. In these instances you have to adjust the script on your own, consult the documentation for the specific build method.

%install and %check

The %install section will oftentimes contain the %py_install and %py2_install macros; you can replace these with the new Python 3 macro %py3_install.

Furthermore, as in the preceding %build section, you will frequently find custom scripts or commands prefixed by either the %{__python} or %{__python2} macros or simply preceded by an invocation of the Python interpreter without the use of macros at all.

In the install section, try substituting it with the new %py3_install macro, which should figure out what to do automatically. If that doesn't work, or if you're porting the %check section, just make sure that any custom scripts or commands are invoked by the new %{__python3} macro.

Lastly, in the %check section you can also encounter a custom Python command that runs the tests, such as nosetests or py.test. In that case find out what is the name of the executable for Python 3 and use it instead of the Python 2 version.

%check
py.test-3
or
nosetests-%{python3_version}

%files

In the files section you can regularly find the following macros: %{python2_sitelib}, %{python2_sitearch}, %{python2_version}, %{python2_version_nodots} or their unversioned alternatives. Substitute these with their counterparts for Python 3, e.g. %{python3_sitelib}.

The files section may also contain the versioned executable, usually %{_bindir}/sample-exec-2.7 in which case it should be substituted by %{_bindir}/sample-exec-%{python3_version}.

.. literalinclude:: specs/application.spec
   :language: spec



.. literalinclude:: specs/application.spec
   :diff: specs/application.spec.orig