[Python-ideas] Nudging beginners towards a more accurate mental model for loop else clauses

[Jan Kaliszewski]

Nick Coghlan dixit (2012-06-08, 19:04):

>   for x in iterable:
>     ...
>   except break:  # Implicit in the semantics of loops
>     pass
>   else:
>     ...
> 
> Would it be worth adding the "except break:" clause to the language
> just to make it crystal clear what is actually going on? I don't think
> so, but it's still a handy way to explain the semantics while gently
> steering people away from linking for/else and if/else too closely.

IMHO a better option would be a separate keyword, e.g. 'broken':

    for x in iterable:
        ...
    broken:
        ...
    else:
        ...

And not only to make the 'else' more understandable.  I found, in
a few situations, that such a 'broken' clause would be really useful,
making my code easier to read and maintain.  There were some relatively
complex, parsing-related, code structures...

    stopped = False
    for x in iterable:
        ...
        if condition1:
            stopped = True
            break
        ...
        if contition2:
            stopped = True
            break
        ...
        if contition3:
            stopped = True
            break
        ...
    if stopped:
        do_foo()
    else:
        do_bar()

It would have been nice to be able to do:

    for x in iterable:
        ...
        if condition1:
            break
        ...
        if contition2:
            break
        ...
        if contition3:
            break
        ...
    broken:
        do_foo()
    else:
        do_bar()

Cheers.
*j