set attributes values
        :param prop:
        :param value:
        :param ef:
        :return:

def set_prop(self, prop, value, ef=None):
        """
        set attributes values
        :param prop:
        :param value:
        :param ef:
        :return:
        """
        if ef:
            # prop should be restricted to n_decoys, an int, the no. of decoys corresponding to a given FPF.
            # value is restricted to the corresponding enrichment factor and should be a float
            self.ef[prop] = value
        else:
            if prop == 'ensemble':
                # value is a tuple of strings that gives the ensemble composition
                self.ensemble = value
            elif prop == 'auc':
                # value is a float that gives the auc value
                self.auc = value