装饰器

装饰器

装饰器(Decorators)是应用包装函数的快捷方式。这有助于将某一功能与一些代码一遍又一
遍地“包装”。举个例子,我为自己创建了一个 retry 装饰器,这样我可以将其运用到任何函
数之中,如果在一次运行中抛出了任何错误,它就会尝试重新运行,直到最大次数 5 次,并
且每次运行期间都会有一定的延迟。这对于你在对一台远程计算机进行网络调用的情况十分
有用:

代码

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# 从time模块引入sleep函数
from time import sleep
from functools import wraps
import logging

logging.basicConfig()
log = logging.getLogger("retry")


def retry(f):
@wraps(f)
def wrapped_f(*args, **kwargs):
MAX_ATTEMPTS = 5
for attempt in range(1, MAX_ATTEMPTS + 1):
try:
return f(*args, **kwargs)
except:
log.exception("Attempt %s %s failed : %s",
attempt, MAX_ATTEMPTS, (args, kwargs))
sleep(10 * attempt)
log.critical("All %s attempts failed : %s",
MAX_ATTEMPTS,
(args, kwargs))

return wrapped_f


counter = 0


@retry
def save_to_database(arg):
print("Write to a database or make a network call or etc.")
print("This will be automatically retried if exception is thrown.")
global counter
counter += 1
# 这将在第一次调用时抛出异常
# 在第二次运行时正常工作(也就是重试)
if counter < 2:
raise ValueError(arg)


# 让你写的脚本模块既可以导入到别的模块中用,另外该模块自己也可执行。
if __name__ == '__main__':
save_to_database("Some bad value")

运行结果

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ERROR:retry:Attempt 1 5 failed : (('Some bad value',), {})
Traceback (most recent call last):
File "E:/PythonProject/more/more_decorators.py", line 16, in wrapped_f
return f(*args, **kwargs)
File "E:/PythonProject/more/more_decorators.py", line 40, in save_to_database
raise ValueError(arg)
ValueError: Some bad value
Write to a database or make a network call or etc.
This will be automatically retried if exception is thrown.
Write to a database or make a network call or etc.
This will be automatically retried if exception is thrown.
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