Calculate lap time.

        Returns:
            float: Lap time. The duration from the previous call of ``lap()``
                 or initialization at first call.
            float: Total time. The duration from initialization.

def lap(self):
        """Calculate lap time.

        Returns:
            float: Lap time. The duration from the previous call of ``lap()``
                 or initialization at first call.
            float: Total time. The duration from initialization.

        """
        now = time.time()
        lap_time = now - self.lap_time
        total_time = now - self.start
        self.lap_time = now
        return lap_time, total_time