def gen():
    yield 1
    yield 2
    return 3

g = gen()
try:
    while True:
        print(next(g), end =" ")
except StopIteration as e:
    print("Returned:", e.value)

def repeater(val):
    while True:
        new = yield val
        if new:
            val = new

g = repeater(10)
print(next(g), end =" ")
print(g.send(20), end =" ")
print(next(g), end =" ")

class MyRange:
    def __init__(self, n):
        self.n = n
        self.i = 0
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= self.n:
            raise StopIteration
        self.i += 1
        return self.i

print(list(MyRange(3)))

def counter():
    i = 0
    while i < 3:
        yield i
        i += 1
    else:
        yield 'done'

print(list(counter()))

def tricky():
    yield from range(2)
    yield from "ab"

print(list(tricky()))

def chain():
    yield from [1, 2]
    yield from (x for x in range(2))

print(list(chain()))

def inner():
    yield from [1, 2]

def outer():
    yield from inner()

print(list(outer()))

def step():
    for i in range(2):
        yield i
    yield from "xy"

print(list(step()))

def gen():
    yield from []
    yield 42

print(next(gen()))

def add_to(val, lst=[]):
    lst.append(val)
    return lst

print(add_to(1), end = " ")
print(add_to(2))