Constructors: Usage of super vs. class.__init__()?

Question

class A: def init(self, x, y): self.x = x self.y = y

    def to_string(self):
        return "x, y = (" + str(self.x) + ", " + str(self.y) + ")"

    def __str__(self):
        return self.to_string()

class B(A):
    def __init__(self, z, *args):
        A.__init__(self, *args)
        self.z = z

    def __str__(self):
        return super().__str__()

class C(A):
    def __init__(self, *args):
        super().__init__(*args)

    def to_string(self):
        return "Klasse C, " + super().to_string()  

Why can one init an instance of A in class C without passing "self" as an argument, while in class B we need to pass "self" as an argument in order to let the code run properly?

Thanks in advance for any help understanding this problem