How to use the psychtoolbox.audio.Slave function in psychtoolbox

if self.sndArr.shape[1] == 1:
                self.stereo = 0
            elif self.sndArr.shape[1] == 2:
                self.stereo = 1
            else:
                raise IOError("Couldn't determine whether array is "
                              "stereo. Shape={}".format(self.sndArr.shape))
        self._nSamples = thisArray.shape[0]
        if self.stopTime == -1:
            self.stopTime = self._nSamples / float(self.sampleRate)
        # set to run from the start:
        self.seek(0)
        self.sourceType = "array"

        if not self.track:  # do we have one already?
            self.track = audio.Slave(self.stream.handle, data=self.sndArr,
                                     volume=self.volume)
        else:
            self.track.stop()
            self.track.fill_buffer(self.sndArr, start_index=1)