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))

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

def f(x, y, z):
    return x + y + z

d1 = {'x': 1, 'y': 2}
d2 = {'y': 3, 'z': 4}

try:
    print(f(**d1, **d2))
except TypeError:
    print("TypeError")