2387 class _orderedsetmixin(object):

  2388     """Mixin class with utility methods for smartsets

  2389 

  2390     This should be extended by smartsets which have the isascending(),

  2391     isdescending() and reverse() methods"""

  2392 

  2393     def _first(self):

  2394         """return the first revision in the set"""

  2395         for r in self:

  2396             return r

  2397         raise ValueError('arg is an empty sequence')

  2398 

  2399     def _last(self):

  2400         """return the last revision in the set"""

  2401         self.reverse()

  2402         m = self._first()

  2403         self.reverse()

  2404         return m

  2405 

  2406     def min(self):

  2407         """return the smallest element in the set"""

  2408         if self.isascending():

  2409             return self._first()

  2410         return self._last()

  2411 

  2412     def max(self):

  2413         """return the largest element in the set"""

  2414         if self.isascending():

  2415             return self._last()

  2416         return self._first()

  2417