我有一个循环,开头为for I,范围为(0,100)。正常情况下,它可以正常运行,但有时由于网络条件而出现故障。目前,我已经设置它,以便在失败时,它将继续在except子句中(继续到I的下一个数字)。
我是否可以将相同的数字重新分配给i,并再次运行失败的循环迭代?
我有一个循环,开头为for I,范围为(0,100)。正常情况下,它可以正常运行,但有时由于网络条件而出现故障。目前,我已经设置它,以便在失败时,它将继续在except子句中(继续到I的下一个数字)。
我是否可以将相同的数字重新分配给i,并再次运行失败的循环迭代?
当前回答
更新2021-12-01:
自2016年6月起,不再维护重试包。 考虑使用活动的fork github.com/jd/tenacity,或者github.com/litl/backoff。
重试包是在失败时重试代码块的好方法。
例如:
@retry(wait_random_min=1000, wait_random_max=2000)
def wait_random_1_to_2_s():
print("Randomly wait 1 to 2 seconds between retries")
其他回答
使用while和计数器:
count = 1
while count <= 3: # try 3 times
try:
# do_the_logic()
break
except SomeSpecificException as e:
# If trying 3rd time and still error??
# Just throw the error- we don't have anything to hide :)
if count == 3:
raise
count += 1
如果你想要一个没有嵌套循环和成功调用break的解决方案,你可以为任何可迭代对象开发一个快速的可检索包装。这里有一个我经常遇到的网络问题的例子——保存的身份验证过期。它的用法是这样的:
client = get_client()
smart_loop = retriable(list_of_values):
for value in smart_loop:
try:
client.do_something_with(value)
except ClientAuthExpired:
client = get_client()
smart_loop.retry()
continue
except NetworkTimeout:
smart_loop.retry()
continue
这里有一个快速装饰器来处理这个问题。7行,没有依赖关系。
def retry(exception=Exception, retries=3, delay=0):
def wrap(func):
for i in range(retries):
try:
return func()
except exception as e:
print(f'Retrying {func.__name__}: {i}/{retries}')
time.sleep(delay)
raise e
return wrap
@retry()
def do_something():
...
@retry(HTTPError, retries=100, delay=3)
def download_something():
...
可以添加的一个功能是扩展异常以处理多个异常(splat一个列表)。
使用递归
for i in range(100):
def do():
try:
## Network related scripts
except SpecificException as ex:
do()
do() ## invoke do() whenever required inside this loop
如果您正在寻找的是重新尝试x次失败的尝试,那么单个for else循环可能就是您想要的。考虑这个例子,尝试了3次:
attempts = 3
for attempt in range(1, attempts+1):
try:
if attempt < 4:
raise TypeError(f"Error raised on attempt: {attempt}")
else:
print(f'Attempt {attempt} finally worked.')
except (TypeError) as error:
print(f'Attempt {attempt} hit the exception.')
continue
else:
break
else:
print(f'Exit after final attempt: {attempt}')
print(f'\nGo on to execute other code ...')
给出输出:
Attempt 1 hit the exception.
Attempt 2 hit the exception.
Attempt 3 hit the exception.
Exit after final attempt: 3
Go on to execute other code ...
再试一次它就成功了
attempts = 4
给出输出:
Attempt 1 hit the exception.
Attempt 2 hit the exception.
Attempt 3 hit the exception.
Attempt 4 finally worked.
Go on to execute other code ...