リクエストライブラリクローラーとは何ですか?使い方？ （例を挙げて説明）

import requests
url = "https://item.jd.com/21508090549.html"
try:
	r = requests.get(url)
	r.raise_for_status()          #检验http状态码是否为200
	r.encoding = r.apparent_encoding#识别页面正确编码
	print(r.text[:1000])
except:
	print("爬取失败")

import requests
url = "https://www.amazon.cn/gp/product/B01M8L5Z3Y"
try:
	#kv = {'user-agent':'Mozilla/5.0'}#假装访问浏览器为Mozilla/5.0
	r = requests.get(url)
	r.raise_for_status()#检验http状态码是否为200
	r.encoding = r.apparent_encoding#识别页面正确编码
	print(r.text[:1000])
except:
	print("爬取失败")

import requests
url = "http://www.baidu.com/s"
keyword="python"
try:
	kv = {'wd':key}
	r = requests.get(url,params=kv)
	print(r.request.url)
	r.raise_for_status()#检验http状态码是否为200
	r.encoding = r.apparent_encoding#识别页面正确编码
	print(len(r.text))#由于信息量可能特别大，这里只输出长度
except:
	print("爬取失败")

import requests
import os
url = "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1540201265460&di=64720dcd3bbc24b7d855454028173deb&imgtype=0&src=http%3A%2F%2Fpic34.photophoto.cn%2F20150105%2F0005018358919011_b.jpg"
root = "D://pics//"
path = root + url.split('.')[-2]+'.'+url.split('.')[-1]#得到文件名，生成文件路径
if not os.path.exists(root):
	os.mkdir(root)#如果目录不存在，创建目录
if not os.path.exists(path):#如果文件不存在爬取文件并保存
	r = requests.get(url)
	with open(path,'wb') as f:#打开文件对象
		f.write(r.content)#写入爬取的图片
		f.close()
		print("文件保存成功")
else:
	print("文件已存在")