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

MRAB python at mrabarnett.plus.com
Sat Jun 9 18:49:48 CEST 2012

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: dofoo() else: dobar() [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()

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