Generators & classes

def fib():
    a, b = 0, 1
    while True:
        yield a
        a, b = b, a + b

from itertools import islice
list(islice(fib(), 20))

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181]

class Vec:
    def __init__(self, *xs): self.xs = xs
    def __add__(self, o): return Vec(*(a + b for a, b in zip(self.xs, o.xs)))
    def __mul__(self, k): return Vec(*(k * a for a in self.xs))
    __rmul__ = __mul__
    def __repr__(self): return f"Vec{self.xs}"

3 * Vec(1, 2) + Vec(0, 1)

Vec(3, 7)

# Coroutines, driven by hand
async def square(x):
    return x * x

async def main():
    total = 0
    for i in range(5):
        total += await square(i)
    return total

c = main()
try:
    c.send(None)
except StopIteration as e:
    print('result', e.value)

result 30