add contracts to groups

def register_combo(self, parent, legs):
        """ add contracts to groups """
        parent = self.ibConn.contractString(parent)
        legs_dict = {}
        for leg in legs:
            leg = self.ibConn.contractString(leg)
            legs_dict[leg] = self.get_instrument(leg)
        self.instrument_combos[parent] = legs_dict