Python網絡爬蟲實例教程——第2章 爬蟲基礎

2.1 認識HTTP請求

2.1.1 HTTP請求的含義

2.1.2 HTTP請求信息

1. 請求方法

2. 請求頭部

2.2 爬蟲基礎-Requests庫入門

2.2.1 Requests庫的安裝

2.2.2 Requests庫的請求方法

import requests

# get 獲取
response = requests.get('https://www.douban.com/')

# post 提交
requests.post('https://www.douban.com/')

2.2.3 Requests庫的響應對象

2.2.4 響應狀態碼

418 反爬蟲
200 正常登錄

import requests

url = 'https://www.douban.com/search'

r = requests.get(url)

# 狀態碼
code = r.status_code
print(code)

沒有定製頭部文件，被反爬蟲了

2.2.5 定製請求頭部

# headers 頭部信息
headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36'}

# 網址
url = 'https://www.douban.com/search'

# get 獲取
r = requests.get(url, headers=headers)

2.2.6 重定向與超時

# timeout=3 3秒內網頁無反應拋出timeout異常
r = requests.get(url, headers=headers, timeout=3)
# 重定向  ，重新定位到網頁，相當於重新訪問，刷新
r.history

2.2.7 傳遞URL參數

import requests

# headers 頭部信息
headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36'}

# 網址
url = 'https://www.douban.com/search'

payload = {'q': 'python', 'cat': '1001'}

# get 獲取
# timeout=3 3秒內網頁無反應拋出timeout異常
r = requests.get(url, headers=headers, timeout=3,params=payload)

url = r.url
print(url)

2.7.1 更改cat

1、搜索全部，不加cat

import requests

# headers 頭部信息
headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36'}

# 網址
url = 'https://www.douban.com/search'

payload = {'q': 'python'}

# get 獲取
# timeout=3 3秒內網頁無反應拋出timeout異常
r = requests.get(url, headers=headers, timeout=3,params=payload)

url = r.url
print(url)

2、搜索圖片，cat=1025

import requests

# headers 頭部信息
headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36'}

# 網址
url = 'https://www.douban.com/search'

payload = {'q': 'python', 'cat': '1025'}

# get 獲取
# timeout=3 3秒內網頁無反應拋出timeout異常
r = requests.get(url, headers=headers, timeout=3,params=payload)

url = r.url
print(url)

2.3 爬蟲基礎——Urllib庫基礎

2.3.1 Urllib庫簡介

2.3.2 發送GET請求

不自定義頭部文件，都會被反爬蟲

2.3.3 模擬瀏覽器發送GET請求

和Requests庫一樣，需要定義頭部纔行

2.3.4 POST發送一個請求

2.3.5 URL解析

1. urlparse: 拆分URL

from urllib.parse import urlparse

# 1. urlparse: 拆分URL
urlparse = urlparse('https://www.douban.com/search?cat=1001&q=python')
print(urlparse)

2. urlunparse: 拼接URL

# 2. urlunparse: 拼接URL
from urllib.parse import urlunparse
data = ['https', 'www.douban.com', '/search', '', 'cat=1001&q=python', '']
print(urlunparse(data))

3.urljoin: 拼接兩個URL

# 3.urljoin: 拼接兩個URL
from urllib.parse import urljoin
urljoin = urljoin('https://www.douban.com', 'accounts/login')
print(urljoin)

4. 總代碼

# -*- coding: utf-8 -*-
from urllib.parse import urlparse

# 1. urlparse: 拆分URL
urlparse = urlparse('https://www.douban.com/search?cat=1001&q=python')
print(urlparse)
# ParseResult(scheme='https',
#             netloc='www.douban.com',
#             path='/search',
#             params='',
#             query='cat=1001&q=python',
#             fragment='')

# 2. urlunparse: 拼接URL
from urllib.parse import urlunparse
data = ['https', 'www.douban.com', '/search', '', 'cat=1001&q=python', '']
print(urlunparse(data))


# 3.urljoin: 拼接兩個URL
from urllib.parse import urljoin
urljoin = urljoin('https://www.douban.com', 'accounts/login')
print(urljoin)

2.4 本章小結及要求