import numpy as np

A = np.matrix([[1,2,3], [4,5,6], [7,8,9]])
x = np.matrix([[1], [0], [0]])

A*x
"""
outputs:
([[1],
  [4],
  [7]])
"""

  # Can be done with arrays as well!
A = np.array([[1,2,3], [4,5,6], [7,8,9]])
x = np.array([[1], [0], [0]])
A.dot(x)  # same output!