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

[Jan Kaliszewski]

16-07-2009, 13:49 Nick Coghlan <ncoghlan at gmail.com> wrote,
(in thread 'Immemorial desire for "do-while"-likeconstruction'):

> Steven D'Aprano wrote:
>> On Thu, 16 Jul 2009 08:50:06 am Jan Kaliszewski wrote:
>>> Hello,
>>>
>>> The issue has been coming back repeatedly:
>>
>> And not very long ago at that.
>
> So often that there's even a PEP* that documents the pros and cons of
> different ideas and points out that a viable syntactic challenger to the
> "while True with inner break" approach has yet to be found.

Maybe the where-statement could be a candidate? Consider an example:

while foo(x) and bar() where:
     foo = SOMETHING
     def bar():
         SOMETHING ELSE
do:
     THE
     LOOP
     BODY

or maybe better:

while foo(x) and bar():
     where:
         foo = SOMETHING
         def bar():
             SOMETHING ELSE
     THE
     LOOP
     BODY

and Daniel's idea of one-def-shortcut also could apply:

while setup(x < y + 9 or bzzz):
     where def setup(cond):
         SETUP
         ACTIONS
         return cond
     THE
     LOOP
     BODY


And what about for-loop?

for i in smartgen():
     where def smartgen():
         SOME ACTIONS
         yield SOMETHING
     THE
     LOOP
     BODY


Cheers,

-- 
Jan Kaliszewski <zuo at chopin.edu.pl>