data = {}
data.setdefault("keys", []).append(1)
data.setdefault("keys", []).append(2)
print(data["keys"])

class A:
    x = 1

class B(A):
    pass

class C(A):
    pass

B.x = 2
A.x = 3

print(C.x)

def make_counter():
    count = 0
    def increment():
        nonlocal count
        count += 1
        return count
    return increment

c1 = make_counter()
c2 = make_counter()
c1()
print(c1(), c2())

from collections import defaultdict

class Tree(defaultdict):
    def __init__(self):
        super().__init__(Tree)

t = Tree()
t['a']['b']['c'] = 10
t['a']['b']['d'] = 20
t['a']['e'] = 5

def count_leaves(d):
    total = 0
    for v in d.values():
        if isinstance(v, dict):
            total += count_leaves(v)
        else:
            total += v
    return total

print(count_leaves(t))

d = {'a': 1, 'b': 2, 'c': 3}
try:
    for k in d:
        del d[k]
    print(len(d))
except RuntimeError:
    print("RuntimeError")

gen = (x for x in range(5))
print(2 in gen, 2 in gen)

tpl = ([],)
tpl[0].extend([1, 2])
print(tpl)

a = 256
b = 256
c = 257
d = 257
print(a is b, c is d)

gen = (x for x in range(3))
a = list(gen)
b = list(gen)
print(a, b)

def modify(x, y=[]):
    y.append(x)
    return sum(y)

result = modify(5) + modify(7) + modify(4)
print(result)