[Gisengryl]

a = [[1,2,3],[4,5,6],[7,8,9]]

col = [x[1] for x in a]
print col

This code prints out the values of the 2nd column. But I don't understand how the List comprehension expression works.

Doesn't x[1] obtain the value of the 2nd row ? Very confused =/

[sepp2k]

a[1] would be the second row, but x isn't a. x is a variable iterating over the elements of a (because you wrote for x in a). So in the first iteration x is equal to a[0]; on the second it's equal to a[1] and so on. So x[1] is equal to a[0][1], then a[1][1] etc.. And that is the second column.

This post has been edited by sepp2k: 05 October 2014 - 03:07 AM

[Gisengryl]

Thanks alot for the clear explanation, I understood now.