newbie q

Bengt Richter bokr at oz.net
Fri Jan 14 01:08:09 CET 2005


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):

 >>> 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.

Regards,
Bengt Richter



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