code: def angle_between(v1, v2):
      
      v1_u = unit_vector(v1)
      v2_u = unit_vector(v2)
      # Don't use `np.dot`, does not work with all shapes
      angle = np.arccos(np.inner(v1_u, v2_u))
      return angle
docs: Returns the angle in radians between vectors 'v1' and 'v2'.
  
      >>> angle_between((1, 0, 0), (0, 1, 0))
      1.5707963267948966
      >>> angle_between((1, 0, 0), (1, 0, 0))
      0.0
      >>> angle_between((1, 0, 0), (-1, 0, 0))
      3.141592653589793