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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 keys(self):
 """ Return all the keys that represent possible attributes and children. :return: list of keys """

        keys = ['text']
        keys.extend([n for (n, t, r) in self.c_attributes.values()])
        keys.extend([v[0] for v in self.c_children.values()])
        return keys