python - 如果在 "yield" block 内完成， "with"-ing 是否会触发 __exit__ 函数？

Question

This question as been asked with respect to returning从 with block 内部，但是屈服怎么样？

block 的 __exit__ 是否在 yield 上被调用，然后如果函数下次被调用，__enter__ 是否被再次调用？还是等待生成器退出 with block (或返回)

举个例子:

def tmp_csv_file():
    tmp_path = 'tmp.csv'
    with open(tmp_path, 'w+') as csv_file:
        yield csv_file # will this close the file?
    os.remove(tmp_path)

Answer 1

这取决于:

• 如果您的生成器函数超出范围(或以其他方式被删除)，则调用 __exit__。

• 如果生成器耗尽，则调用 __exit__。

=> 只要生成器在 with block 中且未耗尽并且保存生成器的变量未被删除，则不会调用 __exit__。

例如:

class Test(object):
    def __init__(self):
        print('init')

    def __enter__(self):
        print('enter')

    def __exit__(self, *args, **kwargs):
        print('exit')


def funfunc():
    with Test():
        yield 1
        yield 2

测试它:

>>> a = funfunc()
>>> next(a)  # no exit
init
enter
1
>>> next(a)  # no exit
2
>>> next(a, 0)  # exit because generator leaves the with-context inside the function
exit
0

或者如果手动删除:

>>> a = funfunc()
>>> next(a)
init
enter
1
>>> del a  # exit because the variable holding the suspended generator is deleted.
exit