使用命令：pip install PyYAML
提示：
Could not fetch URL https://pypi.org/simple/pyyaml/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/pyyaml/ (Cause d by SSLError(SSLError(1, '[SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1123)'))) - skipping ERROR: Could not find a version that satisfies the requirement PyYAML (from versions: none) ERROR: No matching distribution found for PyYAML Could not fetch URL https://pypi.org/simple/pip/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/pip/ (Caused by S SLError(SSLError(1, '[SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1123)'))) - skipping
后面使用这个命令成功下载：pip --default-timeout=100 install PyYAML -i http://pypi.douban.com/simple/ --trusted-host pypi.douban.com
