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

[Arnaud Delobelle]

On 17 Jul 2009, at 03:02, Greg Ewing wrote:
>
>  [...] I would expect
>
>  x[i] = 5 where:
>    x = y
>    i = 7
>
> to be equivalent to
>
>  y[7] = 5
>
> i.e. both x and i are *evaluated* in the where-block
> scope.
>

So would I, given that the statement
	
	x[i] = 5

is the really the same as the expression

	x.__setitem__(i, 5)

> I'm not sure where this leaves us with respect to
> augmented assignment, though. If you follow it to
> its logical conclusion, then
>
>  x += i where:
>    i = 5
>
> should be equivalent to
>
>  x = x.__iadd__(i) where:
>    i = 5
>
> and then the evaluation and rebinding of 'x' would
> happen in different scopes!

Indeed.  But why not simply evaluate the whole statement in the where  
scope, with all names not bound in the where scope declared as nonlocal?

i.e

	x[i], y = foo(a), b where:
   		i = 7
		def foo(x):
			return bar(x, x)

would be equivalent to:

	def _():
		nonlocal x, y, b
		i = 7
		def foo(x):
			return bar(x, x)
		x[i], y = foo(a), b
	_()

-- 
Arnaud