简单python爬虫案例(爬取慕课网全部实战课程信息)

技术选型

下载器是Requests
解析使用的是正则表达式
效果图:

准备好各个包

# -*- coding: utf-8 -*-
import requests #第三方下载器
import re #正则表达式
import json #格式化数据用
from requests.exceptions import RequestException #做异常处理
from multiprocessing import Pool #使用多进程

开始编写代码,new一个py文件

1.requests下载页面

response =requests.get(url)
url:当前需要爬取的链接
requests.get()获取页面

这里需要注意编码的问题;

就像下面这样：

  response = requests.get(url)
        if response.status_code == 200:
            return response.content.decode("utf-8")
        return None

这样返回的就是一个string类型的数据

2.except RequestException:捕捉异常

为了代码更加健壮，我们在可能发生异常的地方做异常捕获

  try:
        response = requests.get(url)
        if response.status_code == 200:
            return response.content.decode("utf-8")
        return None
    except RequestException:
        return None

更多异常介绍官网
http://www.python-requests.org/en/master/_modules/requests/exceptions/#RequestException

到这里，我们就可以编写main方法进行调用程序了

代码如下:

# -*- coding: utf-8 -*-
import requests
from requests.exceptions import RequestException

def get_one_page(url):
    try:
        response = requests.get(url)
        if response.status_code == 200:
            return response.content.decode("utf-8")
        return None
    except RequestException:
        return None


def main():
    url = 'https://coding.imooc.com/?page=1'
    html = get_one_page(url)
    print(html)

if __name__ == '__main__':
    main()

这样就可以把页面下载下来了

接着,就是解析页面

3.正则表达式介绍

re.compile()方法:编译正则表达式

通过一个正则表达式字符串 编译生成 一个字符串对象

re.findall(pattern,html)方法:找到所有匹配的内容

参数:
pattern：编译过的正则表达式
html：用response.content.decode("utf-8")得到的页面内容

def parse_one_page(html):
    pattern = re.compile('<div class="box">.*?lecturer-info.*?<span>(.*?)</span>.*?shizhan-intro-box.*?title=".*?">'
                         '(.*?)</p>.*?class="grade">(.*?)</span>.*?imv2-set-sns.*?</i>'
                         '(.*?)</span>.*?class="big-text">(.*?)</p>.*?shizan-desc.*?>'
                         '(.*?)</p>.*?</div>',re.S)
    items = re.findall(pattern,html)
    for item in items:
    #格式化每一条数据为字典类型的数据
        yield {
            'teacher': item[0],
            'title': item[1],
            'grade': item[2],
            'people':item[3],
            'score': item[4],
            'describe': item[5]
        }

完整代码:

# -*- coding: utf-8 -*-
import requests
import re
from requests.exceptions import RequestException

def get_one_page(url):
    try:
        response = requests.get(url)
        if response.status_code == 200:
            return response.content.decode("utf-8")
        return None
    except RequestException:
        return None

def parse_one_page(html):
    pattern = re.compile('<div class="box">.*?lecturer-info.*?<span>(.*?)</span>.*?shizhan-intro-box.*?title=".*?">'
                         '(.*?)</p>.*?class="grade">(.*?)</span>.*?imv2-set-sns.*?</i>'
                         '(.*?)</span>.*?class="big-text">(.*?)</p>.*?shizan-desc.*?>'
                         '(.*?)</p>.*?</div>',re.S)
    items = re.findall(pattern,html)
    for item in items:
        yield {
            'teacher': item[0],
            'title': item[1],
            'grade': item[2],
            'people':item[3],
            'score': item[4],
            'describe': item[5]
        }

def main():
    url = 'https://coding.imooc.com/?page=1'
    html = get_one_page(url)
    for item in parse_one_page(html):
        print(item)

if __name__ == '__main__':
    main()

保存解析后的数据到本地文件

4.保存文件操作

with open('imooctest.txt','a',encoding='utf-8') as f
		with as :打开自动闭合的文件并设立对象f进行操作
		参数:
		imooctest.txt:文件名字
		a:追加方式
		encoding:编码格式 不这样设置可能保存的数据会乱码
 f.write(json.dumps(content,ensure_ascii =False)+'
')
		 json.dumps:将刚才被格式化后的字典转为字符串
		 ensure_ascii =False  不这样设置可能保存的数据会乱码
		 +'
' 每条数据为一行

代码如下:

# -*- coding: utf-8 -*-
import requests
import re
import json
from requests.exceptions import RequestException

def get_one_page(url):
    try:
        response = requests.get(url)
        if response.status_code == 200:
            return response.content.decode("utf-8")
        return None
    except RequestException:
        return None

def parse_one_page(html):
    pattern = re.compile('<div class="box">.*?lecturer-info.*?<span>(.*?)</span>.*?shizhan-intro-box.*?title=".*?">'
                         '(.*?)</p>.*?class="grade">(.*?)</span>.*?imv2-set-sns.*?</i>'
                         '(.*?)</span>.*?class="big-text">(.*?)</p>.*?shizan-desc.*?>'
                         '(.*?)</p>.*?</div>',re.S)
    items = re.findall(pattern,html)
    for item in items:
        yield {
            'teacher': item[0],
            'title': item[1],
            'grade': item[2],
            'people':item[3],
            'score': item[4],
            'describe': item[5]
        }

def write_to_file(content):
    with open('imooctest.txt','a',encoding='utf-8') as f:
        f.write(json.dumps(content,ensure_ascii=False)+'
')
        f.close()



def main():
    url = 'https://coding.imooc.com/?page=1'
    html = get_one_page(url)
    for item in parse_one_page(html):
        print(item)
        write_to_file(item)

if __name__ == '__main__':
    main()

5.爬取所有页面并以多进程方式

分析页面,会发现,需要爬取的页面如下

https://coding.imooc.com/?page=1
https://coding.imooc.com/?page=2
https://coding.imooc.com/?page=3
https://coding.imooc.com/?page=4

我们需要构造这种格式的页面

url = 'https://coding.imooc.com/?page='+str(page)

主函数可以类似这样:
for i in range(4):
main(i+1)
完整代码:

# -*- coding: utf-8 -*-
import requests
import re
import json
from requests.exceptions import RequestException
from multiprocessing import Pool


def get_one_page(url):
    try:
        response = requests.get(url)
        if response.status_code == 200:
            return response.content.decode("utf-8")
        return None
    except RequestException:
        return None


def parse_one_page(html):
    pattern = re.compile('<div class="box">.*?lecturer-info.*?<span>(.*?)</span>.*?shizhan-intro-box.*?title=".*?">'
                         '(.*?)</p>.*?class="grade">(.*?)</span>.*?imv2-set-sns.*?</i>'
                         '(.*?)</span>.*?class="big-text">(.*?)</p>.*?shizan-desc.*?>'
                         '(.*?)</p>.*?</div>',re.S)
    items = re.findall(pattern,html)
    for item in items:
        yield {
            'teacher': item[0],
            'title': item[1],
            'grade': item[2],
            'people':item[3],
            'score': item[4],
            'describe': item[5]
        }


def write_to_file(content):
    with open('imoocAll.txt','a',encoding='utf-8') as f:
        f.write(json.dumps(content,ensure_ascii=False)+'
')
        f.close()


def main(page):
    url = 'https://coding.imooc.com/?page='+str(page)
    html = get_one_page(url)
    # parse_one_page(html)
    # print(html)
    for item in parse_one_page(html):
        print(item)
        write_to_file(item)



if __name__ == '__main__':
    pool = Pool()
    pool.map(main,[i+1 for i in range(4)])
    # for i in range(4):
    #     main(i+1)

到这里,我们就能够把慕课网上面的全部实战课程的信息爬取下来,拿到这些数据,你就可以做自己喜爱的分析了