在想要获取https站点的资源时，会报出SNIMissingWarning和InsecurePlatformWarning警告
SNIMissingWarning: An HTTPS request has been made, but the SNI (Subject Name Indication) extension to TLS is not available on this platform.
This may cause the server to present an incorrect TLS certificate, which can cause validation failures. For more information, see 
https://urllib3.readthedocs.org/en/latest/security.html#snimissingwarning.
SNIMissingWarning
A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
InsecurePlatformWarning
解决方法：
在cmd中输入：
pip install pyopenssl ndg-httpsclient pyasn1