SimplePrograms challenge

[rzed]

Steven Bethard <steven.bethard at gmail.com> wrote in
news:466F27A3.8000106 at gmail.com: 

> Steve Howell wrote:
>> --- George Sakkis <george.sakkis at gmail.com> wrote:
>>> from itertools import count, ifilter
>>> def sieve():
>>>     seq = count(2)
>>>     while True:
>>>         p = seq.next()
>>>         seq = ifilter(p.__rmod__, seq)
>>>         yield p
> [snip]
>> Is there a way to broaden the problem somehow, so that
>> it can be a longer solution and further down on the
>> page, and so that I can continue to enforce my
>> somewhat arbitrary rule of ordering examples by how
>> long they are?
> 
> How about we just comment it better?
> 
> import itertools
> 
> def iter_primes():
>      # an iterator of all numbers between 2 and +infinity
>      numbers = itertools.count(2)
> 
>      # generate primes forever
>      while True
> 
>          # generate the first number from the iterator,
>          # which should always be a prime
>          prime = numbers.next()
>          yield prime
> 
>          # lazily remove all numbers from the iterator that
>          # are divisible by prime we just selected
>          numbers = itertools.ifilter(prime.__rmod__, numbers)
> 
> I think that's 17-ish, though you could shrink it down by
> removing some of the spaces.
> 
> STeVe

How about including a driver? Generators are frustrating for 
newbies (including oldies new to generators) because they don't 
actually do anything unless you know how to use them. Given the 
above, what's a newbie going to try first? Something like:

>>> iter_primes()

Hmmm. Doesn't do anything.

How about 
>>> for ix in range(10):
...     print iter_primes()

Not what you might expect.

Later:

>>> for ix in range(10):
...     print iter_primes().next()

Hmmmmm....

... and so on.

In much of Python's documentation, and in this case, an occasional 
working example of use would go FAR in aiding understanding of the 
underlying concept.

-- 
rzed