[Python-Dev] switch-based programming in Python (original) (raw)

Skip Montanaro skip@pobox.com (Skip Montanaro)
Thu, 08 Nov 2001 17:23:09 +0100 

>> If you think you need an annotation, you may just as well propose to
>> introduce a switch statement into the language.

mal> True, but that would probably be even harder to get accepted on
mal> python-dev (or would it ;-) ?

>> switch x:
>>   case 'foo':
>>     ...
>>   case 'bar':
>>     ...
>>   case 42:
>>     ...

If you restrict the case values to hashable literals do you need "case"? One new keyword would be easier than two for Guido to swallow...

One other post I saw in this thread used explicit breaks as is required in C. I would get rid of that. When the current case's code ends, control flow should just jump to the end of the switch. No other block in Python falls through like that does it? Leaving out the break statement can also be a subtle source of errors in C code and can probably be eliminated without much loss of expressiveness. Besides, switches (especially those used to implement state machines) are often executed inside loops. If break is used to terminate the current case, it's not available to break out of the enclosing loop and you're stuck with using a try/except/raise combination or setting some state variable and checking it at the bottom of each loop.

Skip