code: def MakeJoint(pmf1, pmf2):
      
      joint = Joint()
      for v1, p1 in pmf1.Items():
          for v2, p2 in pmf2.Items():
              joint.Set((v1, v2), p1 * p2)
      return joint
docs: Joint distribution of values from pmf1 and pmf2.
  
      Args:
          pmf1: Pmf object
          pmf2: Pmf object
  
      Returns:
          Joint pmf of value pairs