How to sum specific array elements in python : I have a simple question, that I hope python can do easily for me. 

I would like to use the sum function on an array. 

The array is a little complicated however it has the following structure: 

[[x1,y1,z1],[x2,y2,z2],..]

I want to sum up all the z elements

sum([[x1,y1,z1],[x2,y2,z2],..]) = z1+z2+...

Can I do this?