重试运行函数的Pythonic方式[重复]

Question

Python 专业人士如何重试运行请求网络服务的函数（网络服务有时会失败）

功能：

def some_request(uri):
    try:
        req = requests.post('http://someuri.com', {'test': 'yes'})
    except Exception as e:
        return False
    return {'id': req.json()['value'], 'other': req.json()['other']}

您使用 while 或其他 python 习语来处理重试？

请告诉我如何以正确的方式进行操作。

Answer 1

定义重试实用程序：

# Retry utility   
# set logging for `retry` channel
import logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger('retry')

# Define Exception class for retry
class RetryException(Exception):
    u_str = "Exception ({}) raised after {} tries."

    def __init__(self, exp, max_retry):
        self.exp = exp
        self.max_retry = max_retry    
    def __unicode__(self):
        return self.u_str.format(self.exp, self.max_retry)
    def __str__(self):
        return self.__unicode__()

# Define retry util function
def retry_func(func, max_retry=10):
    """
    @param func: The function that needs to be retry
    @param max_retry: Maximum retry of `func` function, default is `10`
    @return: func
    @raise: RetryException if retries exceeded than max_retry
    """
    for retry in range(1, max_retry + 1):
        try:
            return func()
        except Exception, e:
            logger.info('Failed to call {}, in retry({}/{})'.format(func.func,
                                                           retry, max_retry))
    else:
        raise RetryException(e, max_retry)

使用它：

from functools import partial
import requests

def some_request(uri, post):
    req = requests.post(uri, post)
    return req

uri = 'http://someuri.com'
post = {'test': 'yes'}

try:
    retry_func(partial(some_request, uri, post), max_retry=3)
except RetryException, e:
    print(e)

输出：

INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): someuri.com
INFO:retry:Failed to call <function some_request at 0x7faaba2318c0>, in retry(1/3)
INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): someuri.com
INFO:retry:Failed to call <function some_request at 0x7faaba2318c0>, in retry(2/3)
INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): someuri.com
INFO:retry:Failed to call <function some_request at 0x7faaba2318c0>, in retry(3/3)
Exception (HTTPConnectionPool(host='someuri.com', port=80): Max retries exceeded with url: / (Caused by <class 'socket.gaierror'>: [Errno -2] Name or service not known)) raised after 3 tries.

Answer 2

我使用的模式重试次数有限，每次尝试之间的睡眠时间间隔很短，呈指数增长，最后在反复失败后引发最后一次看到的异常：

def wrappedRequest( self, uri, args ):
    lastException = None 
    interval = 1.0
    for _ in range(3):
        try:
            result = requests.post(uri, args)
            return result
        except Exception as e:
            lastException = e

        time.sleep(interval)
        interval *= 2.0
    raise lastException 

（我实际上专门检查 HTTPError、URLError、IOError 和 BadStatusLine 异常，而不是广泛的异常网络。）

Answer 3

这肯定需要装饰器。

你可能想要这样的东西：

import functools
def retry(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        retExc = None
        for i in xrange(4):
            try:
                return func(*args, **kwargs)
            except Exception, e:
                retExc = e
        raise retExc
    return wrapper

然后运行您的代码，只需使用：

@retry
def some_request(...):
    ...

你可以通过添加一点睡眠、添加一个 numTimes 来重试等来让它变得更漂亮，但这样就可以了。

Answer 4

这是一个通用装饰器，可让您指定重试次数以及要忽略的异常类型：

from functools import wraps
def retry(count=5, exc_type=Exception):
    def decorator(func):
        @wraps(func):
        def result(*args, **kwargs):
            for _ in range(count):
                try:
                    return func(*args, **kwargs)
                except exc_type:
                    pass
                raise
         return result
     return decorator

像这样使用它：

@retry(count=10, exc_type=IOError)
def read_file():
    pass # do something