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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 etag(self):
 """ Get the ETag option of the message. :rtype: list :return: the ETag values or [] if not specified by the request """

        value = []
        for option in self.options:
            if option.number == defines.OptionRegistry.ETAG.number:
                value.append(option.value)
        return value