Is it possible to not return anything from a function in python? (What happens if the function reaches the end without `return`ing?)

Consider this code:

def foo(foo_input):
    if 0 <= foo_input <= 100:
        return f_input

This returns None in the case where foo_input > 100. But could it actually not return anything? Or does a function always have to return something?

_{See also: return, return None, and no return at all?}

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.

• If you have something to return then do so, if not then don't.
• If you rely on something being returned that has a certain type but you cannot return anything meaningful of this type then None will tell the caller that this was the case ( There is no better way to tell the caller that "nothing" is returned than by None, so check for it and you will be fine)