python爬虫多次请求超时的几种重试方法

第一种方法

headers = Dict()
url = 'https://www.baidu.com'
try:
    proxies = None
    response = requests.get(url, headers=headers, verify=False, proxies=None, timeout=3)
except:
    # logdebug('requests failed one time')
    try:
        proxies = None
        response = requests.get(url, headers=headers, verify=False, proxies=None, timeout=3)
    except:
        # logdebug('requests failed two time')
        print('requests failed two time')

总结：代码比较冗余，重试try的次数越多，代码行数越多，但是打印日志比较方便

第二种方法

def requestDemo(url，):
	headers = Dict()
	trytimes = 3  #  重试的次数
	for i in range(trytimes):
		try:
		    proxies = None
		    response = requests.get(url, headers=headers, verify=False, proxies=None, timeout=3)
		    #	注意此处也可能是302等状态码
		    if response.status_code == 200:
		    	break
		except:
	    	# logdebug(f'requests failed {i}time')
        	print(f'requests failed {i} time')

总结：遍历代码明显比第一个简化了很多，打印日志也方便

第三种方法

def requestDemo(url， times=1):
	headers = Dict()
	try:
	    proxies = None
	    response = requests.get(url, headers=headers, verify=False, proxies=None, timeout=3)
	    html = response.text()
	    #	todo  此处处理代码正常逻辑
	    pass
	    return html
	except:
    	# logdebug(f'requests failed {i}time')
    	trytimes = 3  #  重试的次数
    	if times < trytimes:
    		times += 1
       		return requestDemo(url， times)
       	return 'out of maxtimes'

总结：迭代显得比较高大上，中间处理代码时有其它错误照样可以进行重试；缺点不太好理解，容易出错，另外try包含的内容过多时，对代码运行速度不利。

第四种方法

@retry(3)	#	重试的次数 3
def requestDemo(url):
	headers = Dict()
    proxies = None
    response = requests.get(url, headers=headers, verify=False, proxies=None, timeout=3)
    html = response.text()
    #	todo  此处处理代码正常逻辑
    pass
    return html
   
def retry(times):
    def wrapper(func):
        def inner_wrapper(*args, **kwargs):
            i = 0
            while i < times:
                try:
                    print(i)
                    return func(*args, **kwargs)
                except:
                	#	此处打印日志  func.__name__ 为say函数
                    print("logdebug: {}()".format(func.__name__))
                    i += 1
        return inner_wrapper
    return wrapper

总结：装饰器优点多种函数复用，使用十分方便

第五种方法

#!/usr/bin/python
# -*-coding='utf-8' -*-
import requests
import time
import json
from lxml import etree
import warnings
warnings.filterwarnings("ignore")





def get_xiaomi():
    try:
        # for n in range(5):  # 重试5次
        #     print("第"+str(n)+"次")
        for a in range(5): # 重试5次
            print(a)
            url = "https://www.mi.com/"
            headers = {
                "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3",
                "Accept-Encoding": "gzip, deflate, br",
                "Accept-Language": "zh-CN,zh;q=0.9,en;q=0.8",
                "Connection": "keep-alive",
                # "Cookie": "xmuuid=XMGUEST-D80D9CE0-910B-11EA-8EE0-3131E8FF9940; Hm_lvt_c3e3e8b3ea48955284516b186acf0f4e=1588929065; XM_agreement=0; pageid=81190ccc4d52f577; lastsource=www.baidu.com; mstuid=1588929065187_5718; log_code=81190ccc4d52f577-e0f893c4337cbe4d|https%3A%2F%2Fwww.mi.com%2F; Hm_lpvt_c3e3e8b3ea48955284516b186acf0f4e=1588929099; mstz=||1156285732.7|||; xm_vistor=1588929065187_5718_1588929065187-1588929100964",
                "Host": "www.mi.com",
                "Upgrade-Insecure-Requests": "1",
                "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.90 Safari/537.36"
            }
            response = requests.get(url,headers=headers,timeout=10,verify=False)
            html = etree.HTML(response.text)
            # print(html)
            result = etree.tostring(html)
            # print(result)
            print(result.decode("utf-8"))
            title = html.xpath('//head/title/text()')[0]
            print("title==",title)
            if "左左" in title:
            # print(response.status_code)
            # if response.status_code ==200:
                break
        return title

    except:
        result = "异常"
        return result

if __name__ == '__main__':
    print(get_xiaomi())

第六种方法

Python重试模块retrying

# 设置最大重试次数
@retry(stop_max_attempt_number=5)
def get_proxies(self):
    r = requests.get('代理地址')
    print('正在获取')
    raise Exception("异常")
    print('获取到最新代理 = %s' % r.text)
    params = dict()
    if r and r.status_code == 200:
        proxy = str(r.content, encoding='utf-8')
        params['http'] = 'http://' + proxy
        params['https'] = 'https://' + proxy

# 设置方法的最大延迟时间，默认为100毫秒(是执行这个方法重试的总时间)
@retry(stop_max_attempt_number=5,stop_max_delay=50)
# 通过设置为50，我们会发现，任务并没有执行5次才结束！

# 添加每次方法执行之间的等待时间
@retry(stop_max_attempt_number=5,wait_fixed=2000)
# 随机的等待时间
@retry(stop_max_attempt_number=5,wait_random_min=100,wait_random_max=2000)
# 每调用一次增加固定时长
@retry(stop_max_attempt_number=5,wait_incrementing_increment=1000)

# 根据异常重试，先看个简单的例子
def retry_if_io_error(exception):
    return isinstance(exception, IOError)

@retry(retry_on_exception=retry_if_io_error)
def read_a_file():
    with open("file", "r") as f:
        return f.read()

read_a_file函数如果抛出了异常，会去retry_on_exception指向的函数去判断返回的是True还是False，如果是True则运行指定的重试次数后，抛出异常，False的话直接抛出异常。
当时自己测试的时候网上一大堆抄来抄去的，意思是retry_on_exception指定一个函数，函数返回指定异常，会重试，不是异常会退出。真坑人啊！
来看看获取代理的应用(仅仅是为了测试retrying模块)