The optional “else” in Python loops

Post by maxerickson » Fri, Jul 18, 2014, 12:45 AM UTC

eurleif wrote: post #5

thatswrong0 wrote: post #3

Earlier quoted context omitted.

I agree. I use it, but intuitively, I think of else acting the opposite way - if the loop finishes successfully, great! else, do something.

If you're using break to signal success, that is how else acts.

    >>> for item in (1,2):
    	print(item)
    else:
    	print('Done!')

    1
    2
    Done!
    >>> for item in (1,2):
    	print(item)
    	break
    else:
    	print('Done!')
    
    1
    >>>

    >>> for item in ():
    	print(item)
    else:
    	print('Done')
    
    Done

Post by kazinator » Fri, Jul 18, 2014, 12:47 AM UTC

    (loop for x below 10
                finally (princ "iterated over everything, ") (princ "indeed"))

Post by solox3 » Fri, Jul 18, 2014, 1:19 AM UTC

gejjaxxita wrote: post #14

I always strongly discourage the use of things like this construct in any language. A language is meant to be read not just written. A non-expert python programmer who encounters this will be confused.

Post by andrewchambers » Fri, Jul 18, 2014, 1:59 AM UTC

est wrote: post #16

gejjaxxita wrote: post #14

I always strongly discourage the use of things like this construct in any language. A language is meant to be read not just written. A non-expert python programmer who encounters this will be confused.

> who encounters this will be confused And get it after 30 seconds doc reading?

Post by maxerickson » Fri, Jul 18, 2014, 2:23 AM UTC

BWStearns wrote: post #9

MBlume wrote: post #7

Earlier quoted context omitted.

What finally made it intuitive for me: assuming the loop contains an if condition: break, you can consider the else-clause to be the else of the if statement within the loop.

That logic definitely helps me think about it. But it does seem like a switch from the other wording that python uses. Feels like finally would be more intuitive, whereas without thinking about the search loop case else feels like something that would be triggered by a break or return. I wonder if using the feature would be more common if it was more intuitively worded.

    >>> a=1
    >>> while a>0:
        print(4)
        a=a-1
    else:
        print('done')
        
    4
    done