code: def extract_datetime_hour(cls, datetime_str):
          
          if not datetime_str:
              raise DateTimeFormatterException('datetime_str must a valid string')
  
          try:
              return cls._extract_timestamp(datetime_str, cls.DATETIME_HOUR_FORMAT)
          except (TypeError, ValueError):
              raise DateTimeFormatterException('Invalid datetime string {}.'.format(datetime_str))
docs: Tries to extract a `datetime` object from the given string, including only hours.
  
          Raises `DateTimeFormatterException` if the extraction fails.