pip安装第三方库报错如下：
[root@besttest ld.so.conf.d]# pip3 install xlrd
pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.
Collecting xlrd
Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.")': /simple/xlrd/
Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.")': /simple/xlrd/
Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.")': /simple/xlrd/
Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.")': /simple/xlrd/
Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.")': /simple/xlrd/
Could not fetch URL https://pypi.org/simple/xlrd/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/xlrd/ (Caused by SSLError("Can't connect to HTTPS URL because the SSL module is not available.")) - skipping
Could not find a version that satisfies the requirement xlrd (from versions: )
No matching distribution found for xlrd
You are using pip version 10.0.1, however version 19.2.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
解决方案：
pip3 install xlrd -i http://pypi.douban.com/simple --trusted-host pypi.douban.com
原因：可能资源在国外服务器，导致下载不下来，加上豆瓣，表示去豆瓣源上下载，较国外网址快一些
其他源地址：
1)http://mirrors.aliyun.com/pypi/simple/ 阿里云
2)https://pypi.mirrors.ustc.edu.cn/simple/ 中国科技大学
3) http://pypi.douban.com/simple/ 豆瓣
4) https://pypi.tuna.tsinghua.edu.cn/simple/ 清华大学
5) http://pypi.mirrors.ustc.edu.cn/simple/ 中国科学技术大学