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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 comments(self):
        '''Looks through the last 3 messages and returns those comments.'''
        if self.cache['comments']: return self.cache['comments']
        comments = []
        for message in self.messages[0:3]:
            comment_xml = self.bc.comments(message.id)
            for comment_node in ET.fromstring(comment_xml).findall("comment"):
                comments.append(Comment(comment_node))
        comments.sort()
        comments.reverse()
        self.cache['comments'] = comments
        return self.cache['comments']