why numpy.ndarray is object is not callable in my simple for python loop

Question

I loaded a text file containing a two column matrix (e.g. below)

[ 1   3
  2   4
  3   5 
  2   0]

My calculation is just to sum each row

Answer 1

Avoid loops. What you want to do is:

import numpy as np
data=np.loadtxt(fname="data.txt")## to load the above two column
print data
print data.sum(axis=1)