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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getString(self, index, length, langid = None):
 r"""Retrieve the string descriptor specified by index and langid from a device. Arguments: index: index of descriptor in the device. length: number of bytes of the string (ignored) langid: Language ID. If it is omitted, the first language will be used. """

        return util.get_string(self.dev, index, langid).encode('ascii')