sorry for this question because there are several examples in Stackoverflow. I am writing in order to clarify some of my doubts because I am quite new in Python language.

i wrote a function:

def clipmyfile(inFile,poly,outFile):
... # doing something with inFile and poly and return outFile

Normally I do this:

clipmyfile(inFile="File1.txt",poly="poly1.shp",outFile="res1.txt")
clipmyfile(inFile="File2.txt",poly="poly2.shp",outFile="res2.txt")
clipmyfile(inFile="File3.txt",poly="poly3.shp",outFile="res3.txt")
......
clipmyfile(inFile="File21.txt",poly="poly21.shp",outFile="res21.txt")

I had read in this example Run several python programs at the same time and i can use (but probably i wrong)

from multiprocessing import Pool
p = Pool(21)  # like in your example, running 21 separate processes

to run the function in the same time and speed my analysis

I am really honest to say that I didn't understand the next step.

Thanks in advance for help and suggestion Gianni