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

[Andrey Popp]

Hello,

On Wed, Jul 21, 2010 at 2:48 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> I'll add another issue:
>
> - currently, lexical blocks (indentation following a colon) are used
>  for control flow statements; this proposal blurs the line and makes
>  visual inspection less reliable

Do class definitions or with-statements represent control flow
structures? I think, no (with-statement maybe).

> I also disagree with the rationale which states that the motivation
> is similar to that for decorators or list comprehensions. Decorators
> and list comprehensions add value by making certain constructs more
> concise and more readable (by allowing to express the construct at a
> higher level through the use of detail-hiding syntax); as for
> decorators, they also eliminate the need for repeating oneself. Both
> have the double benefit of allowing shorter and higher-level code.

Consider the following:

...
value = a*x*x + b*x + c given:
    a = compute_a()
    b = compute_b()
    c = compute_c()
...

which is roughly equivalent to

...
a = compute_a()
b = compute_b()
c = compute_c()
value = a*x*x + b*x + c
...

with two differences:

- It emphasizes that `value` is a target of this computation and `a`,
`b` and `c` are just auxiliary.
- It states that `a`, `b` and `c` are only used in statement, before
the `given` keyword, that would help future refactorings.

Due to the second point, it can't be considered as syntactic sugar.

Is is more readable? I think yes.

-- 
Andrey Popp

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