indexing lists/arrays question

[Tim Chase]

On 05/13/2010 12:51 PM, a wrote:
>> If your two arrays are of the same length, you can do things like
>>
>>     a = [2,3,3,4,5,6]
>>     b = ['a', 'b', 'c', 'd', 'e', 'f']
>>
>>     print [m for (n,m) in zip(a,b) if n == 3]
>>
>> and skip the indexes altogether.
>
> mmm, that's clever, thanks.  although i don't know why it works yet.
> at least i found a good user group!

the zip() function takes its parameters and returns a list 
containing paired items from each list:

 >>> print zip(a,b) # using the above-defined a/b
[(2, 'a'), (3, 'b'), (3, 'c'), (4, 'd'), (5, 'e'), (6, 'f')]

The list comprehension then iterates over the elements of that 
list, assigned as (n,m), testing "n" (the numeric value you want 
to test) and returning "m" (the corresponding value in "b")

-tkc