今天在安装retrying时报连接超时错误，最终需要使用国内镜像进行更新..
pip install retrying
Collecting retrying
Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('timed out',))': /simple/retrying/
Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('timed out',))': /simple/retrying/
Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('timed out',))': /simple/retrying/
Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('timed out',))': /simple/retrying/
Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('timed out',))': /simple/retrying/
Could not find a version that satisfies the requirement retrying (from versions: )
No matching distribution found for retrying
推荐使用douban提供的pipy国内镜像服务，如果想手动指定源，可以在pip后面跟-i 来指定源，比如用豆瓣的源来安装retrying框架：
pip install retrying -i http://pypi.douban.com/simple --trusted-host pypi.douban.com
The repository located at pypi.douban.com is not a trusted or secure host and is being ignored. If this repository is available via HTTPS it is recommended to use HTTPS instead, otherwise you may silence this warning and allow it anyways with '--trusted-host pypi.douban.com'.
