Question

Should a function always return a value?

Answer 1

"In Python, functions always return a value. If you don't explicitly return a value, Python assumes the return value is None."
http://www.codepedia.com/1/BeginnersGuideToPython_Functions

Answer 2

As a general statement, yes, a function should always return a value, even if a flag only (None, NULL, etc), as opposed to a procedure that won't return anything. Compare Pascal's procedure, for instance, to Python's def statement.

Answer 3

Python answer
no - sometimes functions are methods that act upon things but don't return anything