Adds a Branch object to the case.

def push_line(self, tokens):
        """ Adds a Branch object to the case.
        """
        logger.debug("Pushing line data: %s" % tokens)

        from_bus = self.case.buses[tokens["fbus"]-1]
        to_bus = self.case.buses[tokens["tbus"]-1]

        e = Branch(from_bus=from_bus, to_bus=to_bus)
        e.r = tokens["r"]
        e.x = tokens["x"]
        e.b = tokens["b"]
        e.rate_a = tokens["s_limit"]
        e.rate_b = tokens["p_limit"]
        e.rate_c = tokens["i_limit"]
        # Optional parameter
        if tokens["tap"] == 0: #Transmission line
            e.ratio = 1.0
        else: # Transformer
            e.ratio = tokens["tap"]
        e.phase_shift = tokens["shift"]
        # Optional parameter
#        if "status" in tokens.keys:
#        e.online = tokens["status"]

        self.case.branches.append(e)