How do I reference a documented Python function parameter using Sphinx markup?

There is no simple way to get a direct reference to a parameter of a function with sphinx and I don’t know an extension for this problem.

The documentation of the python domain explains which objects can be cross referenced.

A possible way to give the user a reference to parameter bar of function foo would be

See parameter ``bar`` in :func:`foo`.

Maybe a direct reference would be possible by writing an extension.