code: def parse(key_string: str) -> 'Key':
          
          parts = key_string.split(Key.PARTITION)
          key_type = KeyType.DIMENSION
          if parts[3]:
              key_type = KeyType.TIMESTAMP
          return Key(key_type, parts[0], parts[1], parts[2].split(Key.DIMENSION_PARTITION)
                     if parts[2] else [],
                     parser.parse(parts[3]) if parts[3] else None)
docs: Parses a flat key string and returns a key