I have a list
a = [[1,2,3],[4,5,6],[7,8,9]]
Now I want to find the average of these inner list so that
a = [(1+4+7)/3,(2+5+8)/
a = [sum(x)/len(x) for x in zip(*a)] # a is now [4, 5, 6] for your example
In Python 2.x, if you don't want integer division, replace sum(x)/len(x) by 1.0*sum(x)/len(x) above.
sum(x)/len(x)
1.0*sum(x)/len(x)
Documentation for zip.