[Python-ideas] 'where' statement in Python?

[Guido van Rossum]

On Wed, Jul 21, 2010 at 11:39 AM, Masklinn <masklinn at masklinn.net> wrote:
> On 2010-07-21, at 02:09 , Carl M. Johnson wrote:
>> Questions:
>>
>> 1.) It looks like a lot of the complexity of PEP 3150 is based on
>> wanting thing like this to work:
>>
>> x[index] = 42 given:
>>    index = complicated_formula
>>
>> To make that work, you need to figure out if index is a nonlocal or a
>> global or what in order to emit the right bytecode. What happens if we
>> just give up that use case and say that anything on the assignment
>> side of the initial = gets looked up in the original namespace? In
>> other words, make 3150 more similar to the sugar:

Why do you think it's more complicated to do it for the LHS than for the RHS?

> I quite agree with that, the where/given block/scope should only apply to the expression directly to the left of it. So only the RHS should be concerned, and LHS is out of that scope.
>
> And that expression would be written as:
>
> operator.setitem(x, index, 42) given:
>    index = complicated_formula

Bah.

> I think the first Torture Test block is misguided, and I'd be -0.5 on such a complex feature.

-- 
--Guido van Rossum (python.org/~guido)