code: def unmap(cls, value):
          
  
          if cls not in _SETUP_CLASSES:
              cls()._setup()
              _SETUP_CLASSES[cls] = True
  
          if cls._map is None:
              raise ValueError(unwrap(
                  '''
                  %s._map has not been defined
                  ''',
                  type_name(cls)
              ))
  
          if not isinstance(value, str_cls):
              raise TypeError(unwrap(
                  '''
                  value must be a unicode string, not %s
                  ''',
                  type_name(value)
              ))
  
          if value in cls._reverse_map:
              return cls._reverse_map[value]
  
          if not _OID_RE.match(value):
              raise ValueError(unwrap(
                  '''
                  %s._map does not contain an entry for "%s"
                  ''',
                  type_name(cls),
                  value
              ))
  
          return value
docs: Converts a mapped unicode string value into a dotted unicode string OID
  
          :param value:
              A mapped unicode string OR dotted unicode string OID
  
          :raises:
              ValueError - when no _map dict has been defined on the class or the value can't be unmapped
              TypeError - when value is not a unicode string
  
          :return:
              A dotted unicode string OID