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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 user_lists(self, username, member_type="USER"):
 """ Look up all the lists that the user is a member of. Args: username (str):
 The MIT username of the user member_type(str):
 The type of user, "USER" or "STRING" Returns: list of strings: names of the lists that this user is a member of """

        return self.client.service.getUserLists(username, member_type, self.proxy_id)