for what are for/while else clauses

[Bengt Richter]

On Fri, 14 Nov 2003 19:31:08 +0100, "Diez B. Roggisch" <deets_noospaam at web.de> wrote:

>Hi,
>
>today I rummaged through the language spec to see whats in the for ... else:
>for me. I was sort of disappointed to learn that the else clauses simply
>gets executed after the loop-body - regardless of the loop beeing entered
>or not.
>
>So where is an actual use case for that feature? 
>
>I imagined that the else-clause would only be executed if the loop body
>wasn't entered, so I could write this
>
>for r in result:
>  print r
>else:
>  print "Nothing found, dude!"
>
>instead of 
>
>if len(result):
>  for r in result
>    print r
>else:
>  print "Nothing found, dude!"
>
>
>
>waiting for enlightment,
>
My mnemonic is to think of the mysterious elses as coming after prefixed pseudo-code like:

if this_code_is_interfered_with:
  <loop code or try block>
else: # got to end of loop or end of try block without interference

hence

 >>> for x in []: pass
 ... else: print 'got to end of nothing without interference ;-)'
 ...
 got to end of nothing without interference ;-)

 >>> try: pass
 ... except: pass
 ... else: print 'got to end of try: without interference.'
 ...
 got to end of try: without interference.

 >>> while raw_input('while> '):
 ...     if raw_input('break? ')=='y': break
 ... else: print 'got to end of while w/o interference'
 ...
 while> asdad
 break? asad
 while> asdasd
 break?
 while>
 got to end of while w/o interference

 >>> while raw_input('while> '):
 ...     if raw_input('break? ')=='y': break
 ... else: print 'got to end of while w/o interference'
 ...
 while> asd
 break? y 

Regards,
Bengt Richter