python爬虫：requests异常requests.exceptions.ConnectionError原因分析及处理

解决方法：

第一种方法：

try:
    response = requests.get(html)
    以下其他运行代码...
except requests.exceptions.ConnectionError:
    r.status_code = "Connection refused"

第二种原因：request的连接数过多而导致Max retries exceeded
在header中不使用持久连接，在headers中加入以下代码：

'Connection': 'close'

第三种原因：请求速度过快导致程序报错：

import time
try:
    response = requests.get(html)
    以下其他运行代码...
except:
        print("requests speed so high,need sleep!")
        time.sleep(5)
        print("continue...")
        continue

原因总结：

1. http的连接数超过最大限制，默认的情况下连接是Keep-alive的，所以这就导致了服务器保持了太多连接而不能再新建连接:a.在headers中修改连接；b.增加多个headers，random调用，如：

user_agent=[
        'Mozilla/5.0 (Linux; U; Android 6.0.1; zh-cn; MI NOTE LTE Build/MMB29M) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/53.0.2785.146 Mobile Safari/537.36 XiaoMi/MiuiBrowser/8.8.7',
        'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Mobile Safari/537.36',
        'Mozilla/5.0 (iPhone; CPU iPhone OS 11_4_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/11.0 Mobile/15E148 Safari/604.1',
        'Mozilla/5.0 (iPhone; CPU iPhone OS 10_2_1 like Mac OS X) AppleWebKit/602.4.6 (KHTML, like Gecko) Version/10.0 Mobile/14D27 Safari/602.1',
        'Mozilla/5.0 (Linux; Android 5.1.1; Nexus 5 Build/LMY48B; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/43.0.2357.65 Mobile Safari/537.36',
        'Mozilla/5.0 (Linux; U; Android-4.0.3; en-us; Galaxy Nexus Build/IML74K) AppleWebKit/535.7 (KHTML, like Gecko) CrMo/16.0.912.75 Mobile Safari/535.7',
        'Mozilla/5.0 (Linux; U; Android-4.0.3; en-us; Xoom Build/IML77) AppleWebKit/535.7 (KHTML, like Gecko) CrMo/16.0.912.75 Safari/535.7',
        'Mozilla/5.0 (Linux;u;Android 4.2.2;zh-cn;) AppleWebKit/534.46 (KHTML,like Gecko) Version/5.1 Mobile Safari/10600.6.3',
        'Mozilla/5.0 (iPhone; CPU iPhone OS 10_3 like Mac OS X) AppleWebKit/602.1.50 (KHTML, like Gecko) CriOS/56.0.2924.75 Mobile/14E5239e YisouSpider/5.0 Safari/602.1',
        'Mozilla/5.0 (Linux; Android 4.0; GT-I9300 Build/IMM76D) AppleWebKit/534.30 (KHTML, like Gecko) Chrome/59.0.3071.92',
        'Mozilla/5.0 (Linux; Android 6.0.1; SOV33 Build/35.0.D.0.326) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.91 Mobile Safari/537.36',
        'Mozilla/5.0 (Linux; Android 6.0; HUAWEI MLA-AL10 Build/HUAWEIMLA-AL10) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Mobile Safari/537.36',
        'Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.96 Mobile Safari/537.36',
        'Mozilla/5.0 (Linux; Android 7.1.1; vivo X20A Build/NMF26X; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/62.0.3202.84 Mobile Safari/537.36 VivoBrowser/5.6.1.1',
        'Mozilla/5.0 (Linux; U; Android 6.0.1; zh-CN; SM-J7108 Build/MMB29K) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/57.0.2987.108 UCBrowser/11.9.7.977 Mobile Safari/537.36',
        'Mozilla/6.0 (Linux; Android 8.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.183 Mobile Safari/537.36'
    ]

3. ip被封，可以设置代理
4. 程序请求速度过快：time.sleep(m)

参考：Python 爬漫画网下载实例