newbie q

[Steve Holden]

Bengt Richter wrote:

> On Thu, 13 Jan 2005 09:16:40 -0500, Steve Holden <steve at holdenweb.com> wrote:
> [...]
> 
>>Any statement of the form
>>
>>    for i in [x for x in something]:
>>
>>can be rewritten as
>>
>>    for i in something:
>>
>>Note that this doesn't mean you never want to iterate over a list 
>>comprehension. It's the easiest way, for example, to iterate over the 
>>first item of each list in a list of lists:
>>
>>    for i in [x[0] for x in something]:
>>
> 
> As I'm sure you know, with 2.4's generator expressions you
> don't have to build the temporary list.
> Which could be important if 'something'
> is (or generates) a huge sequence.
> 
>       for i in (x[0] for x in something):
> 
Yes. While I haven't yet done any more than play with generator 
sequences I do really feel that more of "the best of Icon" has arrived 
in Python with this new addition.

>  >>> something = ([x] for x in xrange(10,20))
>  >>> something
>  <generator object at 0x02EF176C>
>  >>> list(something)
>  [[10], [11], [12], [13], [14], [15], [16], [17], [18], [19]]
>  >>> for i in (x[0] for x in something): print i,
>  ...
> 
> oops, that list() used it up ;-)
> 
>  >>> something = [[x] for x in xrange(10,20)]
>  >>> for i in (x[0] for x in something): print i,
>  ...
>  10 11 12 13 14 15 16 17 18 19
> 
> Really nice.
> 
I quite agree. It's particularly useful for infinite sequences :-)

regards
  Steve
-- 
Steve Holden               http://www.holdenweb.com/
Python Web Programming  http://pydish.holdenweb.com/
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