class A:
    def hello(self):
        return "Hello from A"

class B(A):
    def hello(self):
        return "Hello from B"

b = B()
print(b.hello())

class A:
    @staticmethod
    def stat():
        return "Static"

    @classmethod
    def cls(cls):
        return cls.__name__

    def inst(self):
        return self.__class__.__name__

a = A()

print(A.stat(), A.cls(), a.inst())

class A:
    def __init__(self, value):
        self._x = value

    @property
    def x(self):
        return self._x * 2

a = A(5)
print(a.x)

class A:
    def __str__(self):
        return "Custom str"

a = A()
print(a)

class A:
    def __init__(self, val):
        self.val = val

    def __eq__(self, other):
        return self.val == other.val

a1 = A(3)
a2 = A(3)
print(a1 == a2)

class A:
    def __init__(self):
        print("A", end='')

class B(A):
    pass

b = B()

class A:
    __slots__ = ['x']

a = A()
a.x = 10
a.y = 20
print(a.x)

class Descriptor:
    def __get__(self, obj, objtype=None):
        return 99

class A:
    x = Descriptor()

a = A()
print(a.x)

class Descriptor:
    def __init__(self):
        self.value = 0

    def __get__(self, obj, objtype=None):
        return self.value

    def __set__(self, obj, val):
        self.value = val

class A:
    x = Descriptor()

a = A()
b = A()

a.x = 100
b.x = 200

print(a.x)