网站中很多链接用的是相对路径，直接爬取会产生报错：

Missing scheme in request url: ../index.html

在python3中使用

from urllib.parse import urljoin >>> urljoin("http://www.asite.com/folder/currentpage.html", "anotherpage.html") 'http://www.asite.com/folder/anotherpage.html' >>> urljoin("http://www.asite.com/folder/currentpage.html", "folder2/anotherpage.html") 'http://www.asite.com/folder/folder2/anotherpage.html' >>> urljoin("http://www.asite.com/folder/currentpage.html", "/folder3/anotherpage.html") 'http://www.asite.com/folder3/anotherpage.html' >>> urljoin("http://www.asite.com/folder/currentpage.html", "../finalpage.html") 'http://www.asite.com/finalpage.html'将当前链接与相对路径可以自动拼接。