Generators

# Generator function
def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b

for num in fibonacci(10):
    print(num)

# Generator expression
squares = (x**2 for x in range(1000000))
print(next(squares))

# Infinite generator
def counter(start=0):
    while True:
        yield start
        start += 1