最后在Python 3生成器中尝试

Question

我遇到了一段Python 3代码：

def gen():
    try:
        while True:
            yield 1
    finally:
        print("stop")

print(next(gen()))

运行它之后，我首先想到的输出应该是：

def gen():
    try:
        while True:
            yield 1
    finally:
        print("stop")

print(next(gen()))

但实际上结果是：

1

怎么会这样 引擎盖下发生了什么？

如果我运行for i in gen(): print(i)，将会出现一个无限循环，这正是我所期望的。for和next这里和有什么不一样？

Answer 1

当生成器关闭时循环终止，如果你不保存对它的引用，它会自动发生。一旦发生这种情况，该try语句保证finally在生成器对象被垃圾收集之前执行该块。相比：

>>> next(gen())
stop
1

和

>>> x = gen()
>>> next(x)
1

Answer 2

对生成器对象的垃圾回收执行finally子句。

请考虑以下两种情况：

def gen():
    try:
        while True:
            yield 1
    finally:
        print("stop")

g1 = gen(); print('first time')
print(next(g1))
g2 = gen(); print('second time')  # no stop will be printed because we haven't hit the finally clause yet

def gen():
    try:
        while True:
            yield 1
    finally:
        print("stop")

g = gen(); print('first time')
print(next(g))
g = gen(); print('second time')   # stop will be printed when the first object g was assigned to is garbage collected