def DefaultUpdate(self):
    self.x -= 1    
        
def MyUpdate(self):
    self.x += 1

class A:
    def __init__(self, Update = DefaultUpdate):
        self.update = Update
        self.x = 0

a = A(lambda: MyUpdate(a))
b = A()

a.update()
b.update()

print(a.x)
print(b.x)