Single line if statement with a continue

[MRAB]

On 2022-12-15 19:05, avi.e.gross at gmail.com wrote:
> Multiple returns is not always a problem as it depends on the nature of a
> task whether it has complex enough cases.
> 
> I have seen code that instead sets Boolean variables when it is ready to
> return and everything else keeps checking the variables to skip further
> processing so the program then slides down to a single return statement. If
> done properly, it boils down to the same result if VERY carefully done but
> with lots of sometimes complex IF statements that may be not be updated well
> if the logic changes a bit.
> 
> In such cases, I vastly prefer clean and unambiguous returns  from the
> function right at the point where the decision is made, UNLESS the exit is
> not always clean as there may be cleanup or finalization of some kind
> required that is best done at a single point.
> 
A problem with having a single return is that it can lead to excessive 
indentation:

     if test_1:
         ...

         if test_2:
             ...

             if test_3:
                 ...

     return

With multiple returns, however:

     if not test_1:
         return

     ...

     if not test_2:
         return

     ...

     if not test_3:
         return

     ...

     return

> If efficiency is an issue, then clearly a rapid exit may beat one where
> processing continues for a while and also often beats a method that involves
> creating and calling multiple smaller functions with lots of overhead.
> 
> Having said all that, of course, if you can find a fairly simple algorithm
> that only returns from one place, use it instead of a convoluted one. The
> issue is not necessarily that multiple return points are bad, but that they
> are often a symptom of sloppy planning. But for some problems, they fit well
> and simplify things.
> 
> -----Original Message-----
> From: Python-list <python-list-bounces+avi.e.gross=gmail.com at python.org> On
> Behalf Of Stefan Ram
> Sent: Thursday, December 15, 2022 7:42 AM
> To: python-list at python.org
> Subject: Re: Single line if statement with a continue
> 
> Chris Green <cl at isbd.net> writes:
>>I always try to avoid multiple returns from functions/methods, as soon 
>>as things get complex it's all to easy to miss clean-up etc.
> 
>    This "complexity" could also mean that the function has
>    become too large. In such a case, one could say that the
>    /size/ of the function is the actual cause of problems
>    and not multiple returns.
> 
> |Fools ignore complexity. Pragmatists suffer it. Some can avoid it.
> |Geniuses remove it.
> Alan Perlis (1922/1990)
> 
>    Within a small function, multiple returns are rarely
>    a problem.
> 
>    When a function is large, one can apply well-known
>    refactors. For an example, look at the code in the
>    first post of the thread
> 
> Python script not letting go of files
> Date: Tue, 29 Nov 2022 12:52:15 +0000
> 
>    and then at my reply of
> 
> 29 Nov 2022 14:44:39 GMT.
> 
>>"No multiple returns" is often found in programming guidelines.
> 
>    I religiously followed that when I did more C programming
>    than today. Then, I read an article about how the result
>    pattern makes functions measurably slower. (It should not
>    with an optimizing compiler, but it did due to those
>    measurements. Can't find that article now, though.)
> 
>    "Result pattern" I call writing,
> 
> if a:
>      result = 123
> else:
>      result = 456
> return result
> 
>    , instead of,
> 
> if a:
>      return 123
> else
>      return 456
> 
>    .
> 
> 
> --
> https://mail.python.org/mailman/listinfo/python-list
>