python inheritance

myfirstclass.py

class FirstClass:
    def setdata(self,value):
        self.data = value

    def display(self):
        print(self.data)

class Bclass(FirstClass):
    def concatena(self,arg):
        self.data = arg + ' ' + self.data

class SecondClass(FirstClass, Bclass):
    def display(self):
        print ('current value = "%s"' % self.data)

if __name__ == '__main__':
    
    x = FirstClass()
    y = FirstClass()
    z = SecondClass()

    x.setdata("king arthur")
    y.setdata(3.14159)

    x.display()
    y.display()

    z.setdata('42')
    z.concatena('Hola')
    z.display()