[Tutor] returning None from function definition

[Cameron Simpson]

On 24Oct2020 11:54, Manprit Singh <manpritsinghece at gmail.com> wrote:
>What about returning  None instead of False inside Function
>definition in this case ?

Kipping over the prime functions, I just want to recommend against 
returning None instead of False. Your function returns a true/false 
result, so it _should_ return a Boolean, which in Python is one of the 
two special values True and False.

It _happens_ that your programme runs using None for false, just as it 
would run using 0 for false, because Python falls back to a "nonzero" 
style test in conditions if it is not handed a Boolean (type bool). But 
it is very bad practice.

Secondly, think about linting your programmes. Supposing you put some 
type annotations on your code, like this:

    def prime(n:int) -> bool:
        ... test n for primality ...

If you run a linter over this code which understands type annotations, 
it will rightly complain about returning None, because you've asserted 
that this is a function returning a bool, which is the _natrual_ type 
for logic results.

Finally, all python functions return values. When you just do a plain:

    return

or fall off the end of a function with no explicit return statement, 
that returns None.

Just don't do this.

Cheers,
Cameron Simpson <cs at cskk.id.au>