we are talking about the standard Python functions, not those you have defined in your open files, right?
Those defined in the open files. You must read those files and create tags already, so it should be pretty simple to change them into the whole signature (possibly as a pref). This would be cool, because if you use good arg naming, you know, what you have to pass. And that _really_ improves productivity.
If the above is true, have a look at scripts/create_py_tags.py in the Geany source directory. This script is used to generate the python tags file of the standard functions. And this surely can be improved heavily and since you know Python, it maybe isn't too hard. Any improvements are welcome.
I'll take a look, but since I know neither gtk, nor scintilla, I doubt if this is very fruitful.