<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def datetimes(self):
 """A sorted list of datetimes in this analysis period."""

        if self._timestamps_data is None:
            self._calculate_timestamps()
        return tuple(DateTime.from_moy(moy, self.is_leap_year)
                     for moy in self._timestamps_data)