用于符号数学的Python库。
tutorial
urllib — URL handling modules
Source code: Lib/urllib/
urllib is a package that collects several modules for working with URLs:
urllib.request for opening and reading URLs
urllib.error containing the exceptions raised by urllib.request
urllib.parse for parsing URLs
urllib.robotparser for parsing robots.txt files
Requests is an elegant and simple HTTP library for Python, built for human beings.
Urllib是Python内置模块，Requests是第三方库，Requests是对Urllib的进一步包装，更加的For Human。
