问题描述
class DemoException(Exception):
"""An exception type for the demonstration."""
def demo_exc_handling():
print('-> coroutine started')
while True:
try:
x = yield
except DemoException: # <1>
print('*** DemoException handled. Continuing...')
else: # <2>
print('-> coroutine received: {!r}'.format(x))
finally:
print('-> 1111111111coroutine ending')
raise RuntimeError('This line should never run.')
if __name__ == '__main__':
exc_coro = demo_exc_handling()
next(exc_coro)
exc_coro.send(11)
我得到以下输出：
-> coroutine started
-> coroutine received: 11
-> 1111111111coroutine ending
-> 1111111111coroutine ending
我想知道为什么finally语句执行两次？ 我将非常感谢您的帮助。
解决方法
这与协程或异常无关。只需生成器即可重现：
def demo_exc_handling():
print('-> coroutine started')
while True:
try:
x = yield
finally:
print('-> 1111111111coroutine ending')
raise RuntimeError('This line should never run.')
if __name__ == '__main__':
exc_coro = demo_exc_handling()
next(exc_coro)
next(exc_coro)
以下是输出：
-> coroutine started
-> 1111111111coroutine ending
-> 1111111111coroutine ending
您可能想做的是在try-finally内部进行while循环：
def demo_exc_handling():
print('-> coroutine started')
try:
while True:
x = yield
finally:
print('-> 1111111111coroutine ending')
raise RuntimeError('This line should never run.')
而是输出
-> coroutine started
-> 1111111111coroutine ending
它打印两次，因为即使主程序结束，finally子句也会执行。
协程在主程序结束时第二次产生
让我们产生迭代次数并添加一些打印输出以查看它
class DemoException(Exception):
"""An exception type for the demonstration."""
pass
def demo_exc_handling():
print('-> coroutine started')
i = 1
while True:
try:
print(f"iteration {i}")
x = yield i
except DemoException: # <1>
print('*** DemoException handled. Continuing...')
else: # <2>
print('-> coroutine received: {!r}'.format(x))
finally:
print('-> 1111111111coroutine ending')
i += 1
raise RuntimeError('This line should never run.')
if __name__ == '__main__':
exc_coro = demo_exc_handling()
print("initialised")
y = next(exc_coro)
print(f"got {y}")
exc_coro.send(11)
产生
initialised
-> coroutine started
iteration 1
got 1
-> coroutine received: 11
-> 1111111111coroutine ending
iteration 2
-> 1111111111coroutine ending