<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _update_length(self):
 """ Update the audio length property, according to the length of the current audio data and audio sample rate. This function fails silently if one of the two is ``None``. """

        if (self.audio_sample_rate is not None) and (self.__samples is not None):
            # NOTE computing TimeValue (... / ...) yields wrong results,
            #      see issue #168
            #      self.audio_length = TimeValue(self.__samples_length / self.audio_sample_rate)
            self.audio_length = TimeValue(self.__samples_length) / TimeValue(self.audio_sample_rate)