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)

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

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

from itertools import islice

def infinite_seq():
    n = 1
    while True:
        yield n
        n *= 2

gen = infinite_seq()
result = list(islice(gen, 5))
print(sum(result))

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

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

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