[Python-Dev] PEP 275: "Switching on Multiple Values", Rev 1.1

2001年11月13日 07:52:42 -0500 (EST)

On 2001年11月13日, Skip Montanaro wrote:
>> mal> Syntax:
>> mal> switch EXPR:
> mal> case CONSTANT:
> mal> SUITE 
> mal> case CONSTANT:
> mal> SUITE 
> mal> ...
> mal> else:
> mal> SUITE 
>> mal> (modulo indentation variations)
>> mal> The "else" part is optional. If no else part is given and none
> mal> of the defined cases matches, a ValueError is raised.
>>Hmmm... This doesn't jive well with current if statement semantics. I can
>write 
>> if x == "first":
> dofirst()
>>and no ValueError is raised if x == "second". Why should switch be any
>different?

A switch is a different beast, and should be considered afresh,
and not just as syntactic sugar for a (restricted) if-elif-else list.
However, in all other places Python allows an else clause,
a missing one is treated as ``else: pass'', and I don't see
any compelling reason why a switch should behave otherwise.
	/Paul