def add_to_tail(self):
    self._last = Item(None, self._last)
    if (self._first is None):
        self._first = self._last
    self._count += 1
def add_to_tail(self):
    self._last = Item(None, self._last)
    if (self._first is None):
        self._first = self._last
    self._count += 1