What is the syntax for executing a python function stored in the python hdaModule of a digtal asset within a string parameter field of that asset?

Long story short, we are trying to strip the path and extension off a filename parameter and are using a python function embedded in the HDA to do it. If anyone has other ideas of how to go acout doing this they would be welcome as well.

OK I have a solution, but still would would like to know the answer to the question above.

Right now we run the python function as a callback to the filename parameter and set a hidden string parameter to reference.