<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def next(self, acceleration=0.0):
 """Continue rotation in direction of last drag."""

        q = quaternion_slerp(self._qpre, self._qnow, 2.0 + acceleration, False)
        self._qpre, self._qnow = self._qnow, q