How do I run a function from another script in Python

Lets say FileA and FileB are my two files that do stuff. FileA has as an import FileB has some variables and functions. The Function I want to call in FileA from FileB is X which is using some other variables and functions of FileB. When I try to run the program I get an error saying that "Cannot acces local variable if it's not defined". Now I imagine that it would get all the stuff I declared in FileB but it doesn't. How can I go about this without making my program have a ton of references? Can't I just run my function from FileA while using FileB contents? Note that I am a beginner and it might be a stupid question! And also I will compile the files togheter at the end if it's of any help.

EDIT: If I declare Pas inside my function it does work! But I have too many things to define inside it. Why won't it pick up the context from FileB ?

Example in Code: FileA

import FileB as fb

print(fb.X())

FileB

import random
global Pas
p = "ok"
u = [some randomly generated stuff]

def RandomLetterGen:
   some code

Pas = ""
def X():
 Pas += RandomLetterGen()
 return Pas

This is an easy to understand example but my code does much more to get to the result of the X function in FileB

I tried looking it up online but no luck.