To open .npz traces in python, use the code lines below.

data=np.load(trace_file)
    index = data['index']
    No = data['No'] ; Bo=data['Bo']
    N1 = data['N1'] ; B1=data['B1']
    time = data['time']
    gate_step_size = data['gate_step_size']
    integration_time = data['integration_time']