I was hoping to calculate fields using some rather complicated functions, which I don't think I can realistically write in filemaker.
I would prefer to write a script to extract data into python, perform some procedures and then import it back into filemaker (so a user can see the results "live" in layouts, without having to leave filemaker).
Is this possible in Filemaker Pro?
That python module is meant to work with FileMaker server: send GET/POST requests, get back response in XML, and parse it. Technically you can use it to do a lot (add and delete records, run scripts, etc.) but in your case it won't fit.
There are some plug-ins that can execute shell commands, so this way you can call Python from a command line. Other than that you cannot do this.
But in some time (a few months) there will be a FileMaker plug-in with embedded Python :)