code: def bandwidth(data, period, std=2.0):
      
      catch_errors.check_for_period_error(data, period)
  
      period = int(period)
      bandwidth = ((upper_bollinger_band(data, period, std) -
                   lower_bollinger_band(data, period, std)) /
                   middle_bollinger_band(data, period, std)
                   )
  
      return bandwidth
docs: Bandwidth.
  
      Formula:
      bw = u_bb - l_bb / m_bb