code: def get_ctl_field(self, controlfield, alt=None):
          
          if not alt:
              return self.controlfields[controlfield]
  
          return self.controlfields.get(controlfield, alt)
docs: Method wrapper over :attr:`.controlfields` dictionary.
  
          Args:
              controlfield (str): Name of the controlfield.
              alt (object, default None): Alternative value of the `controlfield`
                  when `controlfield` couldn't be found.
  
          Returns:
              str: record from given `controlfield`