Returns the long date/time string 
        Example: 2018-12-06 12:34

def to_long_datetime_string(self) -> str:
        """ Returns the long date/time string 
        Example: 2018-12-06 12:34
        """
        date_display = self.to_iso_date_string()
        time_display = self.to_short_time_string()
        return f"{date_display} {time_display}"