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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 unicode(self, b, encoding=None):
 """ Convert a byte string to unicode, using string_encoding and decode_errors. Arguments: b: a byte string. encoding: the name of an encoding. Defaults to the string_encoding attribute for this instance. Raises: TypeError: Because this method calls Python's built-in unicode() function, this method raises the following exception if the given string is already unicode: TypeError: decoding Unicode is not supported """

        if encoding is None:
            encoding = self.string_encoding

        # TODO: Wrap UnicodeDecodeErrors with a message about setting
        # the string_encoding and decode_errors attributes.
        return unicode(b, encoding, self.decode_errors)