如何在urllib3的Retry类中使用固定重试间隔而非指数退避？

问题场景 #

想要在urllib3的Retry类中使用固定重试间隔而非指数退避，于是封装了LoggingRetry子类，初始化时指定delay_between_retries=2，但实际重试时该参数始终是默认值0，backoff_factor参数却能正常生效。

问题原因 #

urllib3在处理重试逻辑时，每次重试都会调用Retry类的new()方法生成新的Retry实例，而原代码没有重写这个方法，导致自定义的delay_between_retries属性无法传递给新实例，新实例会使用该参数的默认值0。

解决方案 #

重写LoggingRetry类的new()方法，在创建新实例时将当前实例的delay_between_retries属性传递进去，确保每次重试时该参数都能保留初始设置的值。

修改后的完整代码：

import time
import urllib3
from urllib3.util.retry import Retry
from urllib3.exceptions import MaxRetryError
from requests.exceptions import HTTPError
import traceback

# 带日志的自定义重试策略
class LoggingRetry(Retry):
    def __init__(self, delay_between_retries=0, *args, **kwargs):
        print(f"初始化LoggingRetry，delay_between_retries={delay_between_retries}")
        self.delay_between_retries = delay_between_retries
        super().__init__(*args, **kwargs)

    def sleep(self, response=None):
        backoff = self.get_backoff_time()
        total_sleep_time = self.delay_between_retries + backoff
        print(f"LoggingRetry 睡眠 - delay_between_retries: {self.delay_between_retries}, 退避时间: {backoff}")
        time.sleep(total_sleep_time)

    # 重写new方法，传递自定义参数
    def new(self, **kwargs):
        # 调用父类new方法生成新实例，同步自定义参数
        new_retry = super().new(**kwargs)
        new_retry.delay_between_retries = self.delay_between_retries
        return new_retry

class MyClient:
    def __init__(self, total_tries=3, delay_between_retries=0, backoff_factor=0):
        self.total_tries = total_tries
        self.delay_between_retries = delay_between_retries
        self.backoff_factor = backoff_factor

        # 初始化自定义重试策略
        self.retry_strategy = LoggingRetry(
            total=self.total_tries,
            status_forcelist=[202],
            backoff_factor=self.backoff_factor,
            delay_between_retries=self.delay_between_retries,
            raise_on_status=False,
            allowed_methods=frozenset(['GET'])
        )
        
        # 初始化带重试策略的HTTP客户端
        self.http = urllib3.PoolManager(retries=self.retry_strategy, maxsize=4, block=True)

    
    def request_data(self, url):    
        try:
            response = self.http.request('GET', url,)
            return response
        except MaxRetryError as me:
            print(f"达到最大重试次数: {me}")
        except HTTPError as he:
            print(f"HTTP错误发生: {he}")
            traceback.print_exc()
        except Exception as e:
            print(f"未知错误发生: {e}")
            traceback.print_exc()

MyClient(delay_between_retries=2, backoff_factor=0).request_data(url='http://0.0.0.202/')

验证效果 #

运行修改后的代码，每次重试时会打印出delay_between_retries: 2，说明固定间隔参数已生效，每次重试会睡眠2秒（因backoff_factor=0，总睡眠时长等于固定间隔）。

内容的提问来源于stack exchange，提问作者JMortey