openSUSE:Packaging Python

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The Packaging Python is a step by step introduction on how to build Python software packages for openSUSE and others using the openSUSE Build Service.

The fast and automated way

Lets suppose you want to package zope.interface and you don't know how it is named exactly or where to download from. First of all, you can search for it with py2pack, which can be found in the python-py2pack package and download the source tarball automatically with it if you found the correct module: 

$ py2pack search zope.interface
searching for module zope.interface...
found zope.interface-3.6.1

$ py2pack fetch zope.interface
downloading package zope.interface-3.6.1...
from http://pypi.python.org/packages/source/z/zope.interface/zope.interface-3.6.1.tar.gz

As a next step you may want to generate a package recipe for your distribution. For RPM-based distributions, you want to generate a spec file named python-zopeinterface.spec: 

$ py2pack generate zope.interface -f python-zope.interface.spec

The source tarball and package recipe is all you need to generate the RPM file. This final step may depend on which distribution you use. Again, for openSUSE (and by using the openSUSE Build Service), the complete recipe becomes: 

$ osc mkpac python-zope.interface
$ cd python-zope.interface
$ py2pack fetch zope.interface
$ py2pack generate zope.interface -f python-zope.interface.spec
$ vi *.spec
BuildRequires: python-setuptools
ZZ
$ osc build
$ osc vc
$ osc add *
$ osc commit

The first line uses osc, the Build Service command line tool to generate a new package (preferrably in your Build Service home project). The py2pack steps are known already.

It is always a good idea to review all the dependencies specified in the spec file accordingly to upstream manifest and requirements. Ie. dropping devel dependency in a case where package does not compile anything or adding python-setuptools if needed. Finally, the package is tested (built locally), a changes (package changelog) file is generated (with ‘osc vc’) and the result is sent back to the Build Service for public consumption. However, depending on the Python module, you may have to adapt the generated spec file slightly. Py2pack is quite clever and tries to auto-generate as much as it can, but it depends on the metadata that the module provides. Thus, bad metadata implies mediocre results. To get further help about py2pack usage, issue the following command: 

$ py2pack help

Often, the first run of 'osc build' will fail with build error messages, due to missing python modules. Look for the keyword 'import', this should give you a hint, what needs to be added to the 'BuildRequires:' of you spec-file.

Hints on how to package Python modules manually

Manual packaging is discouraged since we have tools to do that. If you insist on having fun, please consider any package spec file in devel:languages:python. python-pbr, python-mock or python-Twisted are few examples.

In general we are using python single-spec packaging.

What is single-spec?

'Single-spec' (or 'Singlespec') is an approach for packaging both python2 and python3 variants of a Python module from a single source spec file.

Compatibility shims

If your packages are targeted for anything other than Leap 15 or newer, the spec file must include two things:

  • Redefinition of %python_module macro.

    %{?!python_module:%define python_module() python-%{**} python3-%{**}}

  • Build requirement on python-rpm-macros:

    BuildRequires:  python-rpm-macros

Naming policy

SUSE has a policy for names of Python module packages. A module is to Python what shared libraries are to C - a piece of code that doesn't work by itself, but provides functionality to other Python programs.

All Python module packages, whether pure Python or C-based, should be called python-modulename. modulename should be the name of this module on the Python Package Index.

Previously, Python packages have been named after directories in the site-packages hierarchy. Often, this was an arbitrary choice, several modules install more than one directory there. Also, the Python universe includes modules that share the same directory name (search for "daemon" on PyPI) and it was not always easy to find out the right package name. Furthermore, the new approach has several advantages:

This policy doesn't apply to end-user applications that are not designed and planned to be used as libraries - so if you're packaging something that is going to have an icon in the application menu, you should just call the package by its normal name (as found on the Python Package Index).

There are some corner cases as to what is an application and what is a module - for example, many modules come with simple command-line tools that allow you to use a subset of their functionality directly. The rule of thumb is this: if this package is going to be a dependency of some other Python application, apply the naming policy, otherwise keep it just as the module name.

Similarly, this policy doesn't apply to jupyter kernels, extensions, and similar packages that are not designed and planned to be used as libraries. If they are meant to be used exclusively within the confines of a jupyter environment, they should be called jupyter-modulename instead of python-modulename, where modulename is still the the name of this module on the Python Package Index. Such packages must also provide the python-modulename package if they contain python code. Conversely, packages that are primarily python packages but provide jupyter interfaces should either have the python3 version provide jupyter-modulename, or split out the components in the jupyter data directories into their own jupyter-modulename subpackage.

Source URLs

For packages that are available from PyPI, the correct Source URL is the following:

https://files.pythonhosted.org/packages/source/t/tox-%{version}.tar.gz

The preferred hostname is files.pythonhosted.org. All other hostnames (like pypi.io, pypi.org, pypi.python.org) eventually redirect to it. In order to ease this transition you can put in the bellow mentioned link and it will be automatically converted to the proper format by spec-cleaner tool.

The link you get from PyPI will point to some sort of hash, e.g., https://files.pythonhosted.org/packages/99/20/2fd208e75c05975bf6436258f469aa233045b93d195cdb442045de0923cc/tox-2.7.0.tar.gz. We don't want that. The "semantic URL" is still available:
/packages/source/<first letter>/<full name>/<full name>-<version>.<extension>

In some cases, packages are only distributed through PyPI as wheels. These are files with a .whl. extension. In these cases, either the wheels can be packaged manually, or another upstream source can be used if available (such as from github, see below). The path to the wheel file is of the form:

/packages/<python version>/<first letter>/<full name>/<full name>-<version>-<python version>-<abi>-<platform>.whl.

python version is the specific versions of python the wheel supports, such as py3 for python3-only and py2.py3 for both. Note that this appears twice in the URL, and they must match. abi is the architecture-specific abi. Only wheels with the none abi can be used, since others contain pre-compiled libraries. platform is the particular operating system supported. This must be any, since again anything else contains pre-compiled libraries. Some example of full source URLs for wheels are:

https://files.pythonhosted.org/packages/py2.py3/b/bqplot/bqplot-%{version}-py2.py3-none-any.whl
https://files.pythonhosted.org/packages/py3/i/imatlab/imatlab-%{version}-py3-none-any.whl

For some packages, particularly jupyter kernels or extensions, wheels contains important files the source distribution is missing. In these cases, the use of wheels is preferred. You can check for such files by opening the wheel file (it is just a zip file, if you archive reader can't open it you can change the extension) and look for files in the etc or usr directory.

However, in some situations important files are missing from the PyPI archive or wheel. For example they may be missing tests or license files. Such issues should be reported upstream. If it is a single file, like a license file for licenses that require one, and the upstream has a source such as github that includes that file, it is possible to include it and set the source URL to be the "raw" version of the file while waiting for upstream to provide a proper fix. For example:

https://raw.githubusercontent.com/imatlab/imatlab/v%{version}/LICENSE.txt

However, for packages where many files or whole directories are missing, particularly tests, the upstream source should be used. For github, that source is of the form:

https://github.com/numpy/numpy/archive/v1.16.2.tar.gz#/numpy-1.16.2.tar.gz

The #/numpy-1.16.2.tar.gz part at the end is important. If that is left off, the openSUSE:Factory source validator will download a file named v1.16.2.tar.gz instead of numpy-1.16.2.tar.gz, which will cause the source validation to fail.

BuildRequires

BuildRequires are not conditional and apply for the whole spec file. There is no such thing as "if I build for Python 2, I require package foo"; you simply require package foo always.

If you need a package for all available flavors of python, use the %python_module macro. To ilustrate converting from direct dependencies to %python_module: 

BuildRequires: python-setuptools
BuildRequires: python-py >= 1.4

to this: 

BuildRequires: %{python_module setuptools}
BuildRequires: %{python_module py >= 1.4}

Note that the version requirement goes inside the %python_module call.

This is not intended for Requires tag. The %python_module macro is only for BuildRequires

If you only need the package for one flavor of python, simply don't use the macro and state the dependencies directly: 

BuildRequires: python2-enum34
BuildRequires: python3-astroid

If you need to BuildRequire "python", you can instead use %pythons: 

BuildRequires: %{pythons}
Warning: This macro works only on openSUSE Leap 15.0 and newer.

Requires, Provides and similar

In many cases, you don't need to do anything. The single-spec rewriter will convert your Requires to match the generated package. Only make sure the Requires content really matches up setup.py or requirements.txt and there is nothing missing.

Warning: In particular, do not use %python_module for Requires.

Package names in tags Requires (as well as "Requires(pre)" and all the others), Provides, Recommends, Suggests, Obsoletes, Conflicts, Supplements, and Enhances are automatically converted.
The converter takes into account the packageand expression, and %requires_ge and %requires_eq macros. However, support for these must be coded explicitly. If you find an expression that is not converted, please either post it on the packaging ML or file a bug against python-rpm-macros.

If the requirement name starts with "python-", or with the same name as your package (so "python3-bar" in package "python3-foo"), the python name is changed to match that of the generated package.
This also works for "python" itself.
Packaged listed in packageand expression are also converted.

Requirements specific for one python flavor

You can specify that some packages should only be included for some python flavors, by wrapping them in conditionals using the %python_flavor variable 

Requires: python-idna
%if "%{python_flavor}" == "python2"
Requires: python2-enum34
%endif

As a shortcut, for every flavor, there is a %ifpython macro: %ifpython2, %ifpython3 or %ifpypy3. 

%ifpython2
Requires: python2-enum34
%endif

Note that the shortcuts must not be nested in other conditionals, otherwise you can get "%endif without %if" error message. If you need to nest conditionals, use the %python_flavor conditional.

Warning: This does not work for %prep, %build, %install, %check.
The %ifpython sections are copied (or not) to subpackage definitions. Subpackages have their own requirements, file lists and %pre/%post/etc. scriptlets. The scripts from %prep and others is shared. %ifpython will do the wrong thing.

Obsoleting and Providing old symbols

The following sequence: 

Obsoletes: python-distribute < %{version}
Provides:  python-distribute = %{version}

would mean that your python2-package will obsolete/provide python2-distribute and your python3-package will obsolete/provide python3-distribute and your pypy3 package will obsolete/provide pypy3-distribute.
Often, this is not what you want.

First of all, in many cases, this is only applicable for Python 2, so the sequence should be wrapped in %ifpython2 conditional.

Second, you will note that neither package obsoletes/provides python-distribute.
Here is how you do that: 

%define oldpython python
%ifpython2
Obsoletes: %{oldpython}-distribute < %{version}
Provides:  %{oldpython}-distribute = %{version}
%endif


%python_module in Provides

If you are creating a subpackage that will be common for all flavors (could be a -doc subpackage), sometimes you need to provide a symbol for all flavors.

E.g., your package python-foo-doc should also provide python2-foo-doc, python3-foo-doc etc.

In such case, you use the %python_module macro: 

%package -n python-foo-doc
Provides: %{python_module foo-doc = %{version}}

This is also the one case where you could use %python_module in Requires.

(See below on declaring packages with -n to prevent autogeneration.)

%python_subpackages

Easy enough: place the %python_subpackages macro on a separate line at the end of the spec preamble (the part that ends where your package's %description begins). 

Provides: pylint
BuildRoot: %{tmproot}/blabla
BuildArch: noarch

%python_subpackages

%description

This macro emits all the subpackage descriptions, %files and scriptlet sections for the autogenerated parts.

Subpackage declarations

Subpackages are converted automatically. If you have a subpackage %package foo, singlespec will create python3-yourpackage-foo and all the rest from it.

If you want to prevent this, use %package -n %{name}-foo. Or the full name, %package -n python-yourpackage-foo. This will ensure that the subpackage will be skipped.

This also means that packages named %package -n yourpackage-python will not be processed. There will be a mechanism for these in the future.

Common documentation packages

It is very common that the shipped documentation and probably included examples are quire big and should be in a separate sub-package. The package could have - for example - these sections: 

%package -n %{name}-doc
Summary:        Documentation files for %name
Group:          Documentation/Other

%description -n %{name}-doc
HTML Documentation and examples for %name.

%files -n %{name}-doc
%doc examples docs/_build/html/

Build macros

For building the packages use %python_build.
For installing the packages use %python_install.

These macros already contain the usual options (--root, --prefix), so in the typical case, you don't need to supply any options. If you have something specific, you can add it: %python_build --enable-specific-feature.

If you set environment variables, export them first: 

export CFLAGS="-fwrapv"
%python_build

For any other commands, you can use %python_exec. That is also a good way to run pythonic executables. For example: 

%check
%python_exec setup.py extracommand
%python_exec %{_bindir}/nosetests
%python_expand PYTHONPATH=%{buildroot}%{$python_sitelib} py.test-%{$python_version}

%python_expand

For anything more complicated than executing all the interpreters, use the %python_expand macro. This will repeatedly expand the %{$python}, %{$python_sitelib} etc. strings to the currently used flavor. 

%python_expand rm -r %{buildroot}%{$python_sitelib}/file.txt

results in (apart from some build dir manipulations): 

rm -r %{buildroot}%{python2_sitelib}/file.txt
rm -r %{buildroot}%{python3_sitelib}/file.txt
rm -r %{buildroot}%{pypy3_sitelib}/file.txt

IMPORTANT: you can use %python_expand to replace macro definitions, but make sure you use, e.g., %{$python_sitelib}, with the $ sign.
If you use plain %{python_sitelib}, the macro will be expanded before %python_expand can modify it.

A common use for %python_expand is with fdupes, as in: 

%python_expand %fdupes %{buildroot}%{$python_sitelib}/mymodule

You can use multiline %python_expand if you enclose the lines in {}. The only technical limitation is that the first line must not be empty (but can be a comment starting with #): 

%{python_expand # this will expand the following section
%$python_install
mv %{buildroot}%{_bindir}/exename %{buildroot}%{_bindir}/exename-%{$python_bin_suffix}
}

This is eg useful when running tests and some pre-step is needed: 

%check
%{python_expand rm -rf .testrepository
$python -m unittest discover -v                                                                                                                                                                                                                                                               
}

Naming flavor-specific files

Executables specific to a particular flavor should use %python_bin_suffix instead of %python_version for names. This expands to %python_version for CPython, pp%{python_version} for PyPy. If we support Jython, it will get a specific bin_suffix too.

Build directories specific to a particular flavor should use %python_prefix. This expands to the flavor name.

Filelists

If your package is called python-something (that is, the name prefix is "python" and not a specific flavor), you must mark your %files sections with %{python_files} macro.

%files %{python_files}
%{python_sitelib}/foo

%files %{python_files plugins}
%{python_sitelib}/foo-plugins

You can use %ifpython2 and similar to conditionally include some files only in some flavors. In addition, you can use shorthands: 

%files %{python_files}
%{python_sitelib}/foo
%{python_sitelib}/foorun.py*
%python3_only %{_bindir}/foorun
%pycache_only %{python_sitelib}/__pycache__

Use %pycache_only or %ifpycache to mark __pycache__ directories.

Executables

For new packages that carry executables, it is preferred that these are marked %python3_only. That ensures that the executables are only installed for the preferred python flavor, which is Python 3.

If your package functionality depends on version of Python (e.g., test harnesses, source code processors, installers, etc.), you should package executables for all flavors. This is easy if the package itself installs versioned executables. If not, use the %python_clone macro. 

%python_install
%python_clone %{buildroot}%{_bindir}/executable

This macro will copy the executable as executable-%python_bin_suffix for all flavors, and change the shebang line to the appropriate interpreter.

%python_clone works for all kinds of files. If it recognizes a man page extension, it will correctly rename manpage.1 to manpage-%python_bin_suffix.1.

When using %python_clone, you need to list both the original executable *and* the copied executables in your filelist: 

%{_bindir}/executable-%{python_bin_suffix}
%python3_only %{_bindir}/executable

If changing the shebang line is not appropriate or sufficient, you will need to catch the executable after every installation, like this: 

%{python_expand %$python_install
mv %{buildroot}%{_bindir}/executable %{buildroot}%{_bindir}/executable-%{$python_bin_suffix}
}

Python 2 stacks

The recommendation for new code is to provide Python 3.

For packages that are parts of Python 2 stacks that need Python 2.x executables as well it is preferable to use the alternatives approach outlined below.

update-alternatives

Sometimes it is useful to let the user switch the unversioned executable name to one version of the package or another.

Also, if you can't be sure that the user has a Python 3 stack, and want to provide unversioned executable names regardless, update-alternatives is the way to go.

update-alternatives allows you to switch other things (usually man pages) along with executables.

As a prerequisite, you need to have version-specific file names available -- that is, for every file you provide, file-%python_bin_suffix should exist for all flavors. (for manpage.1, the appropriate name is manpage-%python_bin_suffix.1)

First, you need to set up the alternatives in %install section.

  • If you're using %python_clone to create the executable, simply pass -a option: %python_clone -a %{buildroot}%{_bindir}/executable
  • If not, and the file in question is %{_bindir}/something, call %prepare_alternative something
  • If the file is not in %{_bindir}, you have to specify the path: %prepare_alternative -t /path/to/file file. The path is without %buildroot

Second, create the appropriate %post and %postun sections. Make sure that you have the proper requirements: 

Requires(post):   update-alternatives
Requires(postun):  update-alternatives

Then use %python_install_alternative and %python_uninstall_alternative respectively. 

%post
%python_install_alternative exename

%postun
%python_uninstall_alternative exename

Third, mention the alternative, unversioned, in file list 

%python_alternative %{_bindir}/exename

You can examine a full spec file at [1].

Grouped alternatives

The update-alternatives system allows for multiple files in the same group, to be switched together. This is useful if you want to install an executable along with its manpage, or multiple executables belonging to the same function group.

To make use of this, simply specify the files as multiple arguments to %python_install_alternative: 

%{python_install_alternative pylint pylint.1 epylint epylint.1}

The macro can recognize manpage names and handle them correctly, but the first arguments needs always to the an executable. Or you can specify a full path to the file in question.

The first argument to %python_install_alternative is the group name. This is the only argument for %python_uninstall_alternative; you uninstall the whole group by the one name.

Packages for single Python version

Packages that only exist for Python 2 should be left as is. New packages should be called python2-foo. Old packages should be left as python-foo, but you should add Provides: python2-foo. You should also make sure that all BuildRequires and Requires are for "python2" and "python2-foo".

Packages that only exist for Python 3 can be left as is, or they can be converted to singlespec, with %define skip_python2 1. This is to ensure that they can build for PyPy or other flavors in the future. The definition should be made at the top of the spec-file.

Conditionals on Python versions

If you need to differentiate between python versions you can use the following macros:

Macros Example
%python2_version_nodots 27
%python3_version_nodots 36

For example: 

%if %python3_version_nodots > 34
...
%endif

Common Gotchas

Things to look out for (which can also get your submission declined):

  1. If the %python_module redefinition is present, check that it has "python-%{**}" and not "python-%1"
  2. use %python_module for BuildRequires
  3. do NOT use %python_module for Requires
  4. make sure %python_subpackages macro is present
  5. %files sections should be marked as %files %{python_files}
  6. in %python_expand, make sure you use %$python_ macros instead of %python_ macros
  7. use %python_bin_suffix instead of %python_version for distinguishing executables or build directories

Running tests

The python code is not really compiled like C applications. As such it is really easy to distribute something that does not work at all. In order to prevent this all applications must run and pass their tests unless upstream is providing none themselves.

The easiest way to run tests is using the unittest discover mode: 

%python_exec -m unittest discover -v

This of course only works, if the package supports regular python unittests. If this call does not work one has to dig around checking various files in the development repository like .travis.yml or tox.ini.

To run pytest, the macros %pytest and %pytest_arch can be used.

All Macros

The full documentation for all macros defined for singlespec can be found at the GitHub page for python-rpm-macros package.

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