code: def pad(self, start_duration=0.0, end_duration=0.0):
          '''Add silence to the beginning or end of a file.
          Calling this with the default arguments has no effect.
  
          Parameters
          ----------
          start_duration : float
              Number of seconds of silence to add to beginning.
          end_duration : float
              Number of seconds of silence to add to end.
  
          See Also
          --------
          delay
  
          '''
          if not is_number(start_duration) or start_duration < 0:
              raise ValueError("Start duration must be a positive number.")
  
          if not is_number(end_duration) or end_duration < 0:
              raise ValueError("End duration must be positive.")
  
          effect_args = [
              'pad',
              '{:f}'.format(start_duration),
              '{:f}'.format(end_duration)
          ]
          self.effects.extend(effect_args)
          self.effects_log.append('pad')
  
          return self pad(self, start_duration=0.0, end_duration=0.0):
          '''Add silence to the beginning or end of a file.
          Calling this with the default arguments has no effect.
  
          Parameters
          ----------
          start_duration : float
              Number of seconds of silence to add to beginning.
          end_duration : float
              Number of seconds of silence to add to end.
  
          See Also
          --------
          delay
  
          '''
          if not is_number(start_duration) or start_duration < 0:
              raise ValueError("Start duration must be a positive number.")
  
          if not is_number(end_duration) or end_duration < 0:
              raise ValueError("End duration must be positive.")
  
          effect_args = [
              'pad',
              '{:f}'.format(start_duration),
              '{:f}'.format(end_duration)
          ]
          self.effects.extend(effect_args)
          self.effects_log.append('pad')
  
          return self
docs: Add silence to the beginning or end of a file.
          Calling this with the default arguments has no effect.
  
          Parameters
          ----------
          start_duration : float
              Number of seconds of silence to add to beginning.
          end_duration : float
              Number of seconds of silence to add to end.
  
          See Also
          --------
          delay