new_contents: import ipywidgets as ipyw
  import traitlets as t
  import numpy as np
  import bqplot as bq
  import traittypes as tt
  
  M = 1e10
  
  
  class Bus(t.HasTraits):
  
      '''Bus Model'''
  
      name = t.CUnicode(default_value='GenCo0', help='Name of Generator (str)')
      bus_type = t.Enum(
          values=['SWING', 'PQ', 'PV'],
          default_value='PQ',
          help='Bus type',
      )
      real_power_demand = tt.Array(default_value=[0], minlen=1, help='Active power demand (MW)')
      imag_power_demand = tt.Array(default_value=[0], minlen=1, help='Reactive power demand (MVAR)')
      shunt_conductance = t.CFloat(default_value=0, help='Shunt Conductance (TODO: units)')
      shunt_susceptance = t.CFloat(default_value=0, help='Shunt Susceptance (TODO: units)')
      area = t.CUnicode(default_value='0', help='Area the bus is located in')
      voltage_magnitude = t.CFloat(default_value=1.0, help='Voltage magnitude (p.u.)')
      voltage_angle = t.CFloat(default_value=0.0, help='Voltage angle (deg)')
      base_voltage = t.CFloat(default_value=230, help='Base voltage (kV)')
      zone = t.CUnicode(default_value='0', help='Zone the bus is located in')
      maximum_voltage = t.CFloat(default_value=1.05, help='Maximum voltage')
      minimum_voltage = t.CFloat(default_value=0.95, help='Minimum voltage')
  
  
subject: Update bus.py with Bus model