using self-developed modules

[wlp]

I use Win10 and Python 3.7.4.
I wrote a program that contains a number of inline functions and classes followed by a main program. It imports a module that I wrote that contains some functions and classes that are used in multiple programs.
My programs look as follows:

main.py

import sys
from selfwrittenmodule import f1, f2
def if1:
    some lines of code
def if2:
    some lines of code
b = 2
a = if1(b)
c = if2 (b)
print (a, b)

selfwrittenmodule
def f1: