code: def _missing_(cls, value):
          
          if not (isinstance(value, int) and 0 <= value <= 1):
              raise ValueError('%r is not a valid %s' % (value, cls.__name__))
          extend_enum(cls, 'Unassigned [%d]' % value, value)
          return cls(value)
          super()._missing_(value)
docs: Lookup function used when value is not found.