最最最基础的爬虫知识（python、urllib），百度贴吧和有道翻译的实例，内置模块

1. urllib

1.1 python版本的区别

• python2:urlib2、urlib
• python3:把python2中的两个包合成urlib.request

1.2 常用方法

• #向百度网站发起一个请求 得到一个响应结果 用一个变量接收
• response.read()
  注:可以表明编码方式，如response.read().decode(‘utf-8’)，同时也将字节流转化成字符串

1.3 实例

import urllib.request
# #向百度网站发起一个请求 得到一个响应结果 用一个变量接收
# response=urllib.request.urlopen('https://www.baidu.com/')
# print(response.read().decode('utf-8'))
url='https://www.baidu.com/'
headers={
     
    'User-Agent':' Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36'
}

#创建百度请求的数据（网页源码）
# 1. 创建请求的对象（构建用户：User-Agent）

response=urllib.request.Request(url,headers=headers)
# 2.获取相应的对象(urlopen())
res=urllib.request.urlopen(response)
# 3.读取响应对象的内容(read().decode('utf-8'))
html=res.read().decode('utf-8')
print(html)

1.4 十六进制转码

import urllib.parse
url='https://www.baidu.com/s?ie=UTF-8&wd=%E6%B5%B7%E8%B4%BC%E7%8E%8B'

r={
     'wd':'海贼王'}
result=urllib.parse.urlencode(r)
print(result)

2.百度贴吧练习

2.1直接写的方式

话不多说，直接上代码，下面有运行成功截图

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time    : 2020/7/22 19:33
# @Author  : 沐白
# @Site    : 
# @File    : 百度贴吧联系一.py
# @Software: PyCharm

# 需求：1输入要爬取贴吧的主题
# 2.输入爬取的起始页和终止页
# 3.把每一页的内容保存到本地

# 找规律
# https://tieba.baidu.com/f?kw=%E5%85%83%E5%B0%8A&ie=utf-8&pn=0
# https://tieba.baidu.com/f?kw=%E5%85%83%E5%B0%8A&ie=utf-8&pn=50
# https://tieba.baidu.com/f?kw=%E5%85%83%E5%B0%8A&ie=utf-8&pn=100

# 主要在于pn的值

import random
import urllib.request
import urllib.parse
headers_list=[ {
     'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/14.0.835.163 Safari/535.1'},
               {
     'User-Agent':' Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36'}
               ,{
     'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0) Gecko/20100101 Firefox/6.0'}
               ]
headers=random.choice(headers_list)

name=input('请输入贴吧名：')
start=int(input('请输入起始页：'))
end=int(input('请输入结束页：'))

kw={
     'kw':name}
kw=urllib.parse.urlencode(kw)

# 拼接url
for i in range(start,end+1):
    pn=(i-1*50)
    baseurl='https://tieba.baidu.com/f?kw='
    req=baseurl+kw+'&pn='+str(pn)
    res=urllib.request.urlopen(req)
    html=res.read().decode('utf-8')

    filename='第'+str(i)+'页.html'

    with open(filename,'w',encoding='utf-8') as f:
        print('正在爬取第{}页'.format(i))
        f.write(html)

2.2优化成函数后的代码

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time    : 2020/7/22 20:25
# @Author  : 沐白
# @Site    : 
# @File    : 百度贴吧联系二.py
# @Software: PyCharm


import random
import urllib.parse
import urllib.request
# 读取页面


def readPage(url):
    headers_list = [{
     
                        'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/14.0.835.163 Safari/535.1'},
                    {
     
                        'User-Agent': ' Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36'}
        , {
     'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0) Gecko/20100101 Firefox/6.0'}
                    ]
    headers = random.choice(headers_list)
    req=urllib.request.Request(url,headers=headers)
    res=urllib.request.urlopen(req)
    html=res.read().decode('utf-8')
    return html
# 写入文件
def writePage(filename,html):
    with open(filename,'w',encoding='utf-8')as f:
        f.write(html)
        print('写入成功')
# 主函数
def main():
    name=input('请输入贴吧名:')
    start=int(input('请输入起始页:'))
    end=int(input('请输入结束页:'))
    kw={
     'kw':name}
    kw=urllib.parse.urlencode(kw)
    for i in range(start,end+1):
        pn=(i-1)*50
        url='https://tieba.baidu.com/f?'+kw+'&pn='+str(pn)
        html=readPage(url)
        filename='第{}页.html'.format(i)
        writePage(filename,html)
if __name__ == '__main__':
    main()

2.3类的方式

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time    : 2020/7/22 20:41
# @Author  : 沐白
# @Site    : 
# @File    : 百度贴吧练习三.py
# @Software: PyCharm


import urllib.request
import urllib.parse
class BaiduSpider:
    def __init__(self):
        self.headers={
     
    'User-Agent':' Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36'
}
        self.beaseurl='https://tieba.baidu.com/f?'

    def readPage(self,url):
        req=urllib.request.Request(url,headers=self.headers)
        res=urllib.request.urlopen(req)
        html=res.read().decode('utf-8')
        return html

    def writePage(self,filename,html):
        with open(filename,'w',encoding='utf-8')as f:
            f.write(html)
            print('写入成功')
        pass
    def main(self):
        name = input('请输入贴吧名:')
        start = int(input('请输入起始页:'))
        end = int(input('请输入结束页:'))
        kw = {
     'kw': name}
        kw = urllib.parse.urlencode(kw)
        for i in range(start, end + 1):
            pn = (i - 1) * 50
            url = self.beaseurl+ kw + '&pn=' + str(pn)
            html = self.readPage(url)
            filename = '第{}页.html'.format(i)
            self.writePage(filename, html)
        pass

if __name__ == '__main__':
    # 创建类的实例
    spider=BaiduSpider()
    spider.main()

3.有道翻译

**注：**需要将data请求转换成bytes

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time    : 2020/7/22 21:34
# @Author  : 沐白
# @Site    : 
# @File    : 有道翻译.py
# @Software: PyCharm

# 需求:制作一个有道翻译小软件

import urllib.request
import urllib.parse
import json
# 请输入要翻译的内容

key=input('请输入要翻译的内容:')

# 把提交的form表单数据转换成bytes类型数据
data={
     
'i': key,
'from': 'AUTO',
'to': 'AUTO',
'smartresult': 'dict',
'client': 'fanyideskweb',
'salt': '15954251040982',
'sign': '5728388cef63a7407571cbf1b5991361',
'ts': '1595425104098',
'bv': 'a9c3483a52d7863608142cc3f302a0ba',
'doctype': 'json',
'version': '2.1',
'keyfrom': 'fanyi.web',
'action': 'FY_BY_REALTlME'
}

data=urllib.parse.urlencode(data)
# 把data数据转换成字节流数据
data=bytes(data,'utf-8')
#发起请求获取响应
# url需要去掉_o
url='http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule'

headers={
     
    'User-Agent':' Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36'
}
req=urllib.request.Request(url,data=data,headers=headers)
res=urllib.request.urlopen(req)
html=res.read().decode('utf-8')
# 把json类型的字符串转换成字典
r_dict=json.loads(html)
r=r_dict['translateResult']
content=r[0]
print(content)

# print(html)
# {"type":"ZH_CN2EN","errorCode":0,"elapsedTime":1,"translateResult":[[{"src":"你好","tgt":"hello"}]]}