requests高阶 & BS4

1.requests高阶用法

1.requests上传文件操作
2.会话维持: Session对象(重点)
3.设置超时时间: timeout, 请求5秒内没有返回响应, 则抛出异常
4.Prepare Request: 构建request对象, 可以放入队列中实现爬取队列调度

　　

1.requests上传文件操作
        files = {'file': open('filename', 'rb')}
        res = requests.post(url=url, files=files)
​
2.会话维持: Session对象
        from requests import Session
        session = Session()
        res = session.get(url=url, headers=headers)
​
3.设置超时时间: timeout, 请求5秒内没有返回响应, 则抛出异常
        res = requests.get(url=url, headers=headers, timeout=5)
​
4.Prepare Request: 构建request对象, 可以放入队列中实现爬取队列调度
        from requests import Request, Session
        url = '....'
        data = {
            'wd': 'spiderman'
        }
        headers = {
            'User-Agent': '...'
        }
        # 1.实话session对象
        session = Session()
        # 2.构建request对象, 传入必要参数
        req = Request('POST', url, data=data, headers=headers)
        req = Request('GET', url, params=params, headers=headers)
        # 3.应用prepared_request方法将request对象转化为Prepared Request对象
        prepared = session.prepare_request(req)
        # 4.利用session的send方法发送请求
        res = session.send(prepared)

---

2.BeautifulSoup库使用

# BeautifulSoup库介绍:
BeautifulSoup也是一个解析库
BS解析数据是依赖解析器的, BS支持的解析器有html.parser, lxml, xml, html5lib等, 其中lxml解析器解析速度快, 容错能力强.
BS现阶段应用的解析器多数是lxml

　　

# BeautifulSoup 使用步骤:
from bs4 import BeautifulSoup
 
​
soup = BeautifulSoup(res.text, 'lxml')
tag = soup.select("CSS选择器表达式")   # 返回一个列表

　　

CSS选择器:

1.根据节点名及节点层次关系定位标签: 标签选择器  &  层级选择器
soup.select('title')
soup.select('div > ul > li')   # 单层级选择器
soup.select('div li')  # 多层级选择器
​
2.根据节点的class属性定位标签: class选择器(classical)
soup.select('.panel')
​
3.根据id属性定位标签: id选择器
soup.select('#item')
​
4.嵌套选择:
ul_list = soup.select('ul')
for ul in ul_list:
  print(ul.select('li'))
​
# 获取节点的文本或属性:
tag_obj.string: 获取直接子文本-->如果节点内有与直系文本平行的节点, 该方法拿到的是None
tag_obj.get_text(): 获取子孙节点的所有文本
tag_obj['attribute']: 获取节点属性

　　

# 练习示例:
html = '''
    <div class="panel">
        <div class="panel-heading">
            <h4>BeautifulSoup练习</h4>
        </div>
        <div class="panel-body">
            <ul class="list" id="list-1">
                <li class="element">第一个li标签</li>
                <li class="element">第二个li标签</li>
                <li class="element">第三个li标签</li>
            </ul>
            <ul class="list list-small">
                <li class="element">one</li>
                <li class="element">two</li>
            </ul>
            <li class="element">测试多层级选择器</li>
        </div>
    </div>
'''
from bs4 import BeautifulSoup
​
soup = BeautifulSoup(html, 'lxml')
# 1.根据节点名定位节点, 获取其文本
h4 = soup.select('h4')   # 标签选择器
print(h4[0].get_text())
​
# 2.根据class属性定位节点
panel = soup.select('.panel-heading')
print(panel)
​
# 3.根据id属性定位节点
ul = soup.select('#list-1')
print(ul)
​
# 4.嵌套选择
ul_list = soup.select('ul')
for ul in ul_list:
    li = ul.select('li')
    print(li)
    
# 5.单层级选择器与多层级选择器
li_list_single = soup.select(".panel-body > ul > li")
li_list_multi = soup.select(".panel-body li")

​
​

---

# 作业: 爬取整部三国演义销售, 写入txt文件: 'http://www.shicimingju.com/book/sanguoyanyi.html'
​
import requests
from bs4 import BeautifulSoup
​
url = 'http://www.shicimingju.com/book/sanguoyanyi.html'
headers = {
    'User-Agent':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.142 Safari/537.36'
}
res = requests.get(url=url, headers=headers)
soup = BeautifulSoup(res.text, 'lxml')
a_list = soup.select(".book-mulu ul li a")
for item in a_list:
    name = item.string
    href = item["href"]
    # print(href)
    full_url = 'http://www.shicimingju.com' + href
    detail_page = requests.get(url=full_url, headers=headers).text
    soup_detail = BeautifulSoup(detail_page, 'lxml')
    div = soup_detail.select(".chapter_content")[0]
    print(type(div.get_text()))
    with open('%s.txt' % name, 'w', encoding="utf-8") as f:
        f.write(div.get_text())
        
        
# 默写:
会话维持:Session对象
    from requests import Session
    session = Session()
    res = session.get(url=url, headers=headers)
    
# BeautifulSoup 使用步骤:
from bs4 import BeautifulSoup
soup = BeautifulSoup(res.text, 'lxml')
tag = soup.select("CSS选择器表达式")   # 返回一个列表