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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 classic_email_groups(self, client_id=None):
 """Gets the list of classic email groups."""

        if client_id is None:
            response = self._get("/transactional/classicEmail/groups")
        else:
            response = self._get(
                "/transactional/classicEmail/groups?clientID=%s" % client_id)
        return json_to_py(response)