[Python-ideas] Immemorial desire for "do-while"-like construction

[Jan Kaliszewski]

16-07-2009 o 00:54 Chris Rebert <pyideas at rebertia.com> wrote:

> You can fix that by just writing it as:
>
> while True:
>     SOME
>     ACTIONS
>     HERE
>     if not CONDITION: break

Yeah, but it's not the same :) because eyes must look for the actual loop
condition somewhere-within-the-loop (after all, "while True" is common
idiom with large field of usage, not only in such situations...).

Another solution I invented for myself is to use object which once
evaluates to True, then always to False, e.g.:

   from itertools import chain, repeat
class FirstTrue(object):
        def __init__(self):
            self._iter = chain([True], repeat(False))
        def __nonzero__(self):  # __bool__ for Py3k
            return next(self._iter)

Usage:

first = FirstTrue()
while first or CONDITION:
      SOME
      ACTIONS
      HERE

or, if we want to *evaluate* CONDITION also at first time:

first = FirstTrue()
while CONDITION or first:
      SOME
      ACTIONS
      HERE

Wouldn't be nice to have such factory as built-in or in itertools?

Best regards,
*j

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