python - 最后在 Python 3 生成器中尝试

Question

我见过一段 Python 3 代码:

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

print(next(gen()))

运行之后，我一开始以为输出应该是:

1

但实际上结果是:

stop
1

这怎么会发生？幕后发生了什么？

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。这里的for和next有什么区别？

Answer 1

finally 子句正在生成器对象的垃圾回收中执行。

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