[Python-Dev] Enhancing `iter'

[Bob Ippolito]

On Feb 18, 2004, at 8:07 AM, Miki Tebeka wrote:

> Currently `iter' 2'nd parameter is used for comparison.
> I'd like to have the ability to give a function that will determine 
> weather
> to stop or not.
>
> iter(range(10), lambda x: x > 7)
> will stop at 8.
> (There reverse logic might be uses as well: continue as long a 
> `sentinal'
> returns True.)
>
> The only problem I can see is that someone might want to use a function
> object as a sentinal, then `iter' won't know if to call the function 
> or to
> compare. However this seems very rare and can be solved by:
> def f(x, y):
>     ....
> iter(something, lambda x: x == f)

This is not necessary.

 >>> import itertools
 >>> list(itertools.takewhile(lambda x: x < 8, range(10)))
[0, 1, 2, 3, 4, 5, 6, 7]

(among the numerous other ways to say it with itertools .. or even 
generator comprehensions in Python 2.4)

-bob