Any of the above solutions didn't work for me. I got ModuleNotFoundError: No module named whtever
error.
So my solution was importing like below
from . import filename # without .py
inside my first file I have defined function fun like below
# file name is firstFile.py
def fun():
print('this is fun')
inside the second file lets say I want to call the function fun
from . import firstFile
def secondFunc():
firstFile.fun() # calling `fun` from the first file
secondFunc() # calling the function `secondFunc`