在Python中重试功能

Question

前段时间,我需要retryR中的一个函数来处理缓慢的服务器响应.该函数将具有以下行为:(尝试操作(函数或方法),如果失败,请稍等一下,然后重试)x10

我想出了以下内容:

retry <- function(fun, max_trys = 10, init = 0){
  suppressWarnings(tryCatch({
    Sys.sleep(0.3);
    if(init<max_trys) {fun}
}, error=function(e){retry(fun, max_trys, init = init+1)}))}

它运作良好.现在我在Python3中需要相同的东西,所以我尝试制作相同的代码:

import time
def retry_fun(fun, max_trys = 10, init=0):
    try:
        time.sleep(0.3)
        if(init<max_trys):
            fun
    except:
        retry_fun(fun, max_trys, init = init+1)

但是当我运行它时,它会崩溃我的内核.由于我是Python的初学者,我不确定是什么导致了崩溃,以及函数是否/如何作为参数传递到另一个函数.

你能救我吗？

Answer 1

有几个 Python 包：

1. 退避
2. 韧性

退避示例

import backoff

@backoff.on_exception(backoff.expo,
                      (MyPossibleException1,
                       MyPossibleException2))
def your_function(param1, param2):
    # Do something

坚韧的例子

from tenacity import wait_exponential, retry, stop_after_attempt

@retry(wait=wait_exponential(multiplier=2, min=2, max=30),  stop=stop_after_attempt(5))
def your_function(param1, param2):
   # Do something

Answer 2

除了能够传递功能,并通过添加使用他们()的名字(Python的语法调用调用)后,您不要需要使用递归; 把它放在一个循环中:

import time
def retry(fun, max_tries=10):
    for i in range(max_tries):
        try:
           time.sleep(0.3) 
           fun()
           break
        except Exception:
            continue

except Exception应该更改以捕获函数可能引发的有意义的异常.使用Exception(正如我在示例中所做的)通常是不好的做法,因为它捕获了一大堆您可能不想被捕获的异常.

除此之外,使用a for-loop而不是显式的第三个计数器和递归(这导致较大的值的长调用堆栈)更好.

Answer 3

我知道这是一个老问题。但是，我想添加我已经准备好的解决方案。最好的方法是编写一个retry装饰器，它会在发生异常时重试。此外，您还可以设置自定义指数延迟。文档字符串解释了如何使用装饰器。干得好：

import logging
import time
from functools import partial, wraps


def retry(func=None, exception=Exception, n_tries=5, delay=5, backoff=1, logger=False):
    """Retry decorator with exponential backoff.

    Parameters
    ----------
    func : typing.Callable, optional
        Callable on which the decorator is applied, by default None
    exception : Exception or tuple of Exceptions, optional
        Exception(s) that invoke retry, by default Exception
    n_tries : int, optional
        Number of tries before giving up, by default 5
    delay : int, optional
        Initial delay between retries in seconds, by default 5
    backoff : int, optional
        Backoff multiplier e.g. value of 2 will double the delay, by default 1
    logger : bool, optional
        Option to log or print, by default False

    Returns
    -------
    typing.Callable
        Decorated callable that calls itself when exception(s) occur.

    Examples
    --------
    >>> import random
    >>> @retry(exception=Exception, n_tries=4)
    ... def test_random(text):
    ...    x = random.random()
    ...    if x < 0.5:
    ...        raise Exception("Fail")
    ...    else:
    ...        print("Success: ", text)
    >>> test_random("It works!")
    """

    if func is None:
        return partial(
            retry,
            exception=exception,
            n_tries=n_tries,
            delay=delay,
            backoff=backoff,
            logger=logger,
        )

    @wraps(func)
    def wrapper(*args, **kwargs):
        ntries, ndelay = n_tries, delay

        while ntries > 1:
            try:
                return func(*args, **kwargs)
            except exception as e:
                msg = f"{str(e)}, Retrying in {ndelay} seconds..."
                if logger:
                    logging.warning(msg)
                else:
                    print(msg)
                time.sleep(ndelay)
                ntries -= 1
                ndelay *= backoff

        return func(*args, **kwargs)

    return wrapper