摘要：百度云搜索搜網(wǎng)盤(pán)如果爬蟲(chóng)沒(méi)有異常處理，那么爬行中一旦出現(xiàn)錯(cuò)誤，程序?qū)⒈罎⑼Ｖ构ぷ?，有異常處理即使出現(xiàn)錯(cuò)誤也能繼續(xù)執(zhí)行下去常見(jiàn)狀態(tài)碼重定向到新的，永久性重定向到臨時(shí)，非永久性請(qǐng)求的資源未更新非法請(qǐng)求請(qǐng)求未經(jīng)授權(quán)禁止訪問(wèn)沒(méi)找到對(duì)應(yīng)頁(yè)面服務(wù)器內(nèi)部

如果爬蟲(chóng)沒(méi)有異常處理，那么爬行中一旦出現(xiàn)錯(cuò)誤，程序?qū)⒈罎⑼Ｖ构ぷ鳎挟惓Ｌ幚砑词钩霈F(xiàn)錯(cuò)誤也能繼續(xù)執(zhí)行下去

1.常見(jiàn)狀態(tài)碼

301：重定向到新的URL，永久性
302：重定向到臨時(shí)URL，非永久性
304：請(qǐng)求的資源未更新
400：非法請(qǐng)求
401：請(qǐng)求未經(jīng)授權(quán)
403：禁止訪問(wèn)
404：沒(méi)找到對(duì)應(yīng)頁(yè)面
500：服務(wù)器內(nèi)部出現(xiàn)錯(cuò)誤
501：服務(wù)器不支持實(shí)現(xiàn)請(qǐng)求所需要的功能

2.異常處理

URLError捕獲異常信息

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import urllib.request
import urllib.error

try:                                    #嘗試執(zhí)行里面的內(nèi)容
    html = urllib.request.urlopen("http://www.xiaohuar.com/").read().decode("utf-8")
    print(html)

except urllib.error.URLError as e:      #如果出現(xiàn)錯(cuò)誤
    if hasattr(e,"code"):               #如果有錯(cuò)誤代碼
        print(e.code)                   #打印錯(cuò)誤代碼
    if hasattr(e,"reason"):             #如果有錯(cuò)誤信息
        print(e.reason)                 #打印錯(cuò)誤信息

#返回   說(shuō)明網(wǎng)站禁止了爬蟲(chóng)訪問(wèn)
# 403
# Forbidden

瀏覽器偽裝技術(shù)

很多網(wǎng)站，做了反爬技術(shù)，一般在后臺(tái)檢測(cè)請(qǐng)求頭信息里是否有User-Agent瀏覽器信息，如果沒(méi)有說(shuō)明不是瀏覽器訪問(wèn)，就屏蔽了這次請(qǐng)求

所以，我們需要偽裝瀏覽器報(bào)頭來(lái)請(qǐng)求

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import urllib.request
url = "https://www.qiushibaike.com/"                    #抓取頁(yè)面URL
tou = ("User-Agent","Mozilla/5.0 (Windows NT 10.0; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0")  #設(shè)置模擬瀏覽器報(bào)頭
b_tou = urllib.request.build_opener()               #創(chuàng)建請(qǐng)求對(duì)象
b_tou.addheaders=[tou]                              #添加報(bào)頭
html = b_tou.open(url).read().decode("utf-8")       #開(kāi)始抓取頁(yè)面
print(html)

注意：我們可以看到這次請(qǐng)求并不是用urlopen()方法請(qǐng)求的，此時(shí)用urlopen()無(wú)法請(qǐng)求，但是我們就會(huì)感覺(jué)到這樣很費(fèi)勁，難道每次請(qǐng)求都要?jiǎng)?chuàng)建build_opener()，所以我們需要設(shè)置使用urlopen()方法請(qǐng)求自動(dòng)報(bào)頭

設(shè)置使用urlopen()方法請(qǐng)求自動(dòng)報(bào)頭，也就是設(shè)置用戶(hù)代理

install_opener()將報(bào)頭信息設(shè)置為全局，urlopen()方法請(qǐng)求時(shí)也會(huì)自動(dòng)添加報(bào)頭

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import urllib.request
#設(shè)置報(bào)頭信息
tou = ("User-Agent","Mozilla/5.0 (Windows NT 10.0; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0")  #設(shè)置模擬瀏覽器報(bào)頭
b_tou = urllib.request.build_opener()               #創(chuàng)建請(qǐng)求對(duì)象
b_tou.addheaders=[tou]                              #添加報(bào)頭到請(qǐng)求對(duì)象
#將報(bào)頭信息設(shè)置為全局，urlopen()方法請(qǐng)求時(shí)也會(huì)自動(dòng)添加報(bào)頭
urllib.request.install_opener(b_tou)

#請(qǐng)求
url = "https://www.qiushibaike.com/"
html = urllib.request.urlopen(url).read().decode("utf-8")
print(html)

創(chuàng)建用戶(hù)代理池

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import urllib.request
import random   #引入隨機(jī)模塊文件

def yh_dl():    #創(chuàng)建用戶(hù)代理池
   yhdl = [
       "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-us) AppleWebKit/534.50 (KHTML, like Gecko) Version/5.1 Safari/534.50",
       "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0",
       "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)",
       "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0.1) Gecko/20100101 Firefox/4.0.1",
       "Mozilla/5.0 (Windows NT 6.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1",
       "Opera/9.80 (Macintosh; Intel Mac OS X 10.6.8; U; en) Presto/2.8.131 Version/11.11",
       "Opera/9.80 (Windows NT 6.1; U; en) Presto/2.8.131 Version/11.11",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Maxthon 2.0)",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; TencentTraveler 4.0)",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; The World)",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; 360SE)",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Avant Browser)",
       "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)",
       "Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5",
       "User-Agent:Mozilla/5.0 (iPod; U; CPU iPhone OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5",
       "Mozilla/5.0 (iPad; U; CPU OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5",
       "Mozilla/5.0 (Linux; U; Android 2.3.7; en-us; Nexus One Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1",
       "Opera/9.80 (Android 2.3.4; Linux; Opera Mobi/build-1107180945; U; en-GB) Presto/2.8.149 Version/11.10",
       "Mozilla/5.0 (Linux; U; Android 3.0; en-us; Xoom Build/HRI39) AppleWebKit/534.13 (KHTML, like Gecko) Version/4.0 Safari/534.13",
       "Mozilla/5.0 (BlackBerry; U; BlackBerry 9800; en) AppleWebKit/534.1+ (KHTML, like Gecko) Version/6.0.0.337 Mobile Safari/534.1+",
       "Mozilla/5.0 (compatible; MSIE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0; HTC; Titan)",
       "UCWEB7.0.2.37/28/999",
       "NOKIA5700/ UCWEB7.0.2.37/28/999",
       "Openwave/ UCWEB7.0.2.37/28/999",
       "Mozilla/4.0 (compatible; MSIE 6.0; ) Opera/UCWEB7.0.2.37/28/999"
       ]
   thisua = random.choice(yhdl)                    #隨機(jī)獲取代理信息
   headers = ("User-Agent",thisua)                 #拼接報(bào)頭信息
   opener = urllib.request.build_opener()          #創(chuàng)建請(qǐng)求對(duì)象
   opener.addheaders=[headers]                     #添加報(bào)頭到請(qǐng)求對(duì)象
   urllib.request.install_opener(opener)           #將報(bào)頭信息設(shè)置為全局，urlopen()方法請(qǐng)求時(shí)也會(huì)自動(dòng)添加報(bào)頭

#請(qǐng)求
yh_dl()     #執(zhí)行用戶(hù)代理池函數(shù)
url = "https://www.qiushibaike.com/"
html = urllib.request.urlopen(url).read().decode("utf-8")
print(html)

這樣爬蟲(chóng)會(huì)隨機(jī)調(diào)用，用戶(hù)代理，也就是隨機(jī)報(bào)頭，保證每次報(bào)頭信息不一樣