How does one declare a dependency on gi.repository in setup.py (and required C library)?

Question

I am packaging a python application that depends on several C libraries through gobject introspection. I would like to make sure that, at least, the python module from the glib is installed (that is the gi module, packaged as python-gi in Debian, I am not talking about the deprecated PyGObject module). Adding it as a regular dependency makes the install fail, since it is not in Pypi.

How should I declare this ? I looked a setuptool doc and nothing I see quite does the trick.

Thanks.

Related question:

• Bundling GTK3+ with py2exe

Answer 1

You cannot specify non-Python dependencies using setuptools (AFAIK, that is ...).

The install_requires keywords to setuptools.setup can specify Python-style dependencies only; it targets the Python packaging infrastructure. Python-style installer programs (either pip, easy_install or python setup.py install) will resolve such dependencies using strategies to find and resolve Python-style packages only. One of those strategies is using a package index like PyPI.

If you want to create a package that has Debian-style dependencies, which are resolved by Debian-style installers, using Debian package repos, you have to create a Debian package. There are tools that support creating Debian packages from Python projects, for example easydeb and stdeb. However, most people recommend going the extra-mile and explicitly create a Debian package.

In the general case, packaging for and distributing Python projects via PyPI should be the way to go. It's platform and distro independent, and plays nicely with Python-specific installers like pip and tools like virtualenv or buildout. Having a dependency to PyGI would involve documenting the fact to users, like e.g. the pydbus packages does in its README:

It’s based on PyGI, the Python GObject Introspection bindings, which is the recommended way to use GLib from Python. Unfortunately, PyGI is not packaged on pypi, so you need to install it from your distribution’s repository (usually called python-gi, python-gobject or pygobject3).

Your project could also be defensive when importing from PyGI, presenting users a digestible error message like "please sudo apt-get install python-gi" or so, when the import fails.