class A:
    def f(self):
        print("A", end="")
class B(A):
    def f(self):
        print("B", end="")
        super().f()
        A.f(self)
class C(A):
    def f(self):
        print("C", end="")
        super().f()
        A.f(self)
class D(B, C):
    def f(self):
        print("D", end="")
        super().f()
d = D()
d.f()

class A:
    x = 1
    l = []
a1, a2 = A(), A()
a1.x = 2
a1.l.append(100)
print(a2.x, len(a2.l))

d = {}
d[2, 3] = "a", "b"

class C:
    listing = []  
    
x = C()  
x.listing.append(1)
x.listing.append(1)
x.listing = 1
print(x.listing, C.listing)

def f():
    setattr(f, "x", getattr(f, "x", 0) + 1)
    f.f = f
    return f
x = f()()().f.f.f().f.x
print(x)

class A:
    __x = 1

a = A()

class A:
    __x = 1
    def f(self):
        return "f from A"
    
    def g(self):
        return "g from A"

class B:
    __x = 2
    def f(self):
        return "f from B"
    
    def g(self):
        return "g from B"

class C(A, B):
    f = B.f
    
c = C()
print(c.f(), c.g(), c._A__x, c._B__x)

def intersect(*seqs):
    if len(seqs) > 2:
        return intersect(seqs[0], intersect(*seqs[1:]))
    seq1, seq2 = seqs[0], seqs[1]
    res = []
    for x in seq1:
        if x in seq2:
            res.append(x)    
    return res

x = intersect([1, 2, "a", "b"], (1, 4, "b"), {1, "b", "c"}) 
print(x)

def f(n):
    return 0 if n == 0 else 2**n + f(n-1)
print(f(3))

def f():
    x = 1
    y = 1
    def g():
        nonlocal x
        x, y = 2, 2
    g()
    print(x, y)

f()