In version 0.9:

• For a discrete-time system , the time vector should be optional in the forced response (as stated in the documentation).
  However, this code does not work for me:

sys = control.drss(states=1, outputs=1, inputs=1)
u = np.random.randn(1000)
control.forced_response(sys, U=u)

• Also, the default value of return_x is stated to be True in the docstring, but it is None (False?) in the code.