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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 _get_voltage_angle_var(self, refs, buses):
 """ Returns the voltage angle variable set. """

        Va = array([b.v_angle * (pi / 180.0) for b in buses])

        Vau = Inf * ones(len(buses))
        Val = -Vau
        Vau[refs] = Va[refs]
        Val[refs] = Va[refs]

        return Variable("Va", len(buses), Va, Val, Vau)