[Tutor] when do I use this?

[Gonçalo Rodrigues]

Em Mon, 15 Mar 2004 15:39:33 -0900, Tim Johnson <tim at johnsons-web.com>
atirou este peixe aos pinguins:

>* Christopher Spears <cspears2002 at yahoo.com> [040315 15:22]:
>> Several times I have iterated over a sequence with
>> some code that looks like this:
> 
>  I'm going to put in my two cents worth because
>  I've thus far taken a very simplistic approach
>  to iteration myself:
>
>> for f in range(len(files)):
> 
>  Suppose one had several sequences that were of the
>  same length. Then with the approach above, one
>  could use <f> to access each of them.
>
>  However, I believe that there are more 'elegant'
>  and 'pythonesque' ways of iterating over multiple
>  sequences, so I'm looking forward to more comments.
>

Use zip.

>>> help(zip)
Help on built-in function zip:

zip(...)
    zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]
    
    Return a list of tuples, where each tuple contains the i-th
element
    from each of the argument sequences.  The returned list is
truncated
    in length to the length of the shortest argument sequence.

>>>

For example, the following should give you a clue (it also uses tuple
unpacking):

>>> lst = ["some", "list", "of", "words"]
>>> print zip(range(len(lst)), lst)
[(0, 'some'), (1, 'list'), (2, 'of'), (3, 'words')]
>>> for index, word in zip(range(len(lst)), lst):
... 	print "lst[%d]=%s" % (index, word)
... 	
lst[0]=some
lst[1]=list
lst[2]=of
lst[3]=words

With my best regards,
G. Rodrigues