Returns a human-readable string representation with iso date and time
        Example: 2018-12-06 12:32:56

def to_datetime_string(self) -> str:
        """ Returns a human-readable string representation with iso date and time
        Example: 2018-12-06 12:32:56
        """
        date_display = self.to_iso_date_string()
        time_display = self.to_long_time_string()
        return f"{date_display} {time_display}"