Descriptor vs Instance Attribute

class Descriptor:
    def __get__(self, obj, objtype):
        return 100

class A:
    x = Descriptor()

a = A()
a.x = 50
print(a.x)

Late Binding in Closures

funcs = []

for i in range(3):
    funcs.append(lambda: i)

print([f() for f in funcs])

MRO Resolution Order

class A:
    def show(self):
        print("A")

class B(A):
    def show(self):
        print("B")

class C(A):
    def show(self):
        print("C")

class D(B, C):
    pass

D().show()

Mutable Default + Generator

def f(x, cache=[]):
    cache.append(x)
    yield sum(cache)

g1 = f(1)
g2 = f(2)

print(next(g1), next(g2))

Hashing & Mutability

d = {}
x = (1, [2, 3])
d[x] = "value"
print(d)

__slots__ vs __dict__

class A:
    __slots__ = ('x',)

a = A()
a.x = 10
a.y = 20
print(a.x)

Async Execution Order

import asyncio

async def main():
    print(1)
    await asyncio.sleep(0)
    print(2)

asyncio.run(main())

Metaclass Execution Timing

class Meta(type):
    def __new__(cls, name, bases, dct):
        print(name)
        return super().__new__(cls, name, bases, dct)

class A(metaclass=Meta):
    pass

class B(A):
    pass