code: def parse_sort_key(identity: str, sort_key_string: str) -> 'Key':
          
          parts = sort_key_string.split(Key.PARTITION)
          key_type = KeyType.DIMENSION
          if parts[2]:
              key_type = KeyType.TIMESTAMP
          return Key(key_type, identity, parts[0], parts[1].split(Key.DIMENSION_PARTITION)
                     if parts[1] else [],
                     parser.parse(parts[2]) if parts[2] else None)
docs: Parses a flat key string and returns a key