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

[MRAB]

On 09/06/2012 17:01, Jan Kaliszewski wrote:
> 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()
>
[snip]
That can be re-written as:

     stopped = True
     for x in iterable:
         ...
         if condition1:
             break
         ...
         if condition2:
             break
         ...
         if condition3:
             break
         ...
     else:
         stopped = False
     if stopped:
         do_foo()
     else:
         do_bar()