class Base:
    cls = "BASE"
    def do(self, var):
        return f"{self.cls} - {var}"

class Sub1(Base):
    cls = "SUB1"
    def do(self, vars):
        return " + ".join(super().do(var) for var in vars)

class Sub2(Base):
    cls = "SUB2"
    def do(self, vars):
        do = super().do
        return " + ".join(do(var) for var in vars)


sub1 = Sub1()
sub2 = Sub2()
data = "alpha beta gamma delta".split()
print(sub2.do(data))
print(sub1.do(data))