I don't think this usage of ":data:" is correct.
It is supposed to be used for references to module global objects
 -- http://sphinx-doc.org/domains.html#cross-referencing-python-objects
Despite what it says there, it possibly does also apply to local args, as this does seems to work for "call_func" in the \__init__ docstring.

But I don't think it can be applied to 'function' here, as that isn't a named key, so it just renders as highlighted text (no link).

The same thing applies lots more times below...