code: def cartesian_to_spherical_polar(x, y, z):
      
      return numpy.arccos(z / cartesian_to_spherical_rho(x, y, z))
docs: Calculates the polar angle in spherical coordinates from Cartesian
      coordinates. The polar angle is in [0,pi].
  
      Parameters
      ----------
      x : {numpy.array, float}
          X-coordinate.
      y : {numpy.array, float}
          Y-coordinate.
      z : {numpy.array, float}
          Z-coordinate.
  
      Returns
      -------
      theta : {numpy.array, float}
          The polar angle.