with a simple filter that test input against a range 0-100.
if 0 <= foo_input <= 100:
foo_input is > 100
Functions always return something (at least
None, when no return-statement was reached during execution and the end of the function is reached).
Another case is when they are interrupted by exceptions.
In this case exception handling will "dominate over the stack" and you will return to the appropriate
except or get some nasty error :)
Regarding your problem I must say there are two possibilities: Either you have something to return or you do not have.
Nonewill tell the caller that this was the case ( There is no better way to tell the caller that "nothing" is returned then by
None, so check for it and you will be fine)