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

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

class A:
    def __new__(cls):
        return 42
        
    def __init__(self):
        print("Init")

print(A())

class Point:
    __slots__ = ['x', 'y']

p = Point()
p.x = 1
p.z = 2
print(p.x)

def add_item(val, target=[]):
    target.append(val)
    return target

print(add_item(1), add_item(2))

colors = ['red', 'green', 'blue']
colors.insert(1, colors.pop())
colors.reverse()
print(colors[0])

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

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))