python用from gevent import monkey; monkey.patch_all()之后报ssl等错误

　　楼主今天第一次用python基于greenlet实现的第三方协程库gevent，由于gevent在切换IO操作（文件IO、网络IO）时是自动完成的，所以gevent需要通过修改Python自带的一些阻塞式系统调用的标准库，包括socket、ssl、threading和 select等模块，而变为协程，这一过程需要在启动时通过monkey patch完成。

import gevent
from gevent import monkey
monkey.patch_all()

　　楼主遇到的报错如下(简略版，只保留了前半部分报错内容)：

Traceback (most recent call last):
File "/usr/local/python3.6/lib/python3.6/site-packages/gevent/greenlet.py", line 536, in run
result = self._run(*self.args, **self.kwargs)
File "test.py", line 14, in req
res = requests.get(url)
File "/usr/local/python3.6/lib/python3.6/site-packages/requests/api.py", line 72, in get
return request('get', url, params=params, **kwargs)
File "/usr/local/python3.6/lib/python3.6/ssl.py", line 459, in options
super(SSLContext, SSLContext).options.set(self, value)
[Previous line repeated 316 more times]

解决方案：

　　仔细阅读官方文档发现有这样一段Tip：

Tip: 
When monkey patching, it is recommended to do so as early as possible in the lifetime of the process. 
If possible, monkey patching should be the first lines executed. 
Monkey patching later, especially if native threads have been created, atexit or signal handlers have been installed, or sockets have been created, 
may lead to unpredictable results including unexpected LoopExit errors.

即，monkey patching需要放到第一行导入，否则会报错，所以，把 from gevent import monkey；monkey.patch_all() 放到文件最前面就好啦

注：

　　1、monkey patching 官方文档地址

　　2、如果你用的python3.6，推荐使用asyncio