[Python-ideas] Where-statement (Proposal for function expressions)

[David Stanek]

On Fri, Jul 17, 2009 at 4:20 AM, Daniel
Stutzbach<daniel at stutzbachenterprises.com> wrote:
> On Thu, Jul 16, 2009 at 9:02 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
> wrote:
>>
>> I would expect x to be bound in the current scope,
>> not the where-block scope. But I would expect
>>
>>  x[i] = 5 where:
>>    x = y
>>    i = 7
>>
>> to be equivalent to
>>
>>  y[7] = 5
>
> How about if attempts to re-bind variables in outer scopes should throw an
> exception?  Much like they already do in this example:
>
>>>> x = 5
>>>> def foo():
> ...   blah = x
> ...   x = 6
> ...
>>>> foo()
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "<stdin>", line 2, in foo
> UnboundLocalError: local variable 'x' referenced before assignment
>
> (rebinding is allowed if "global" or "nonlocal" is explicitly used, of
> course)
>

This thread is a little confusing to me. I am failing to see how the where
block makes anything clearer. The fact that a new scope is created and names
are available during a singe line of execution scares me.

I also worry that this will encourage code duplication. Any substantial logic
should be rolling into a function not into a where block.

-- 
David
blog: http://www.traceback.org
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