Reference: http://2.python-requests.org/zh_CN/latest/user/advanced.html#advanced
Reference: http://2.python-requests.org/zh_CN/latest/api.html#sessionapi
Reference: http://2.python-requests.org/zh_CN/latest/user/advanced.html#advanced
Reference: http://2.python-requests.org/zh_CN/latest/api.html#sessionapi