当使用pip install或者pip install --upgrade报错
Can‘t roll back cryptography; was not uninstalled
可以进行以下的尝试：
sudo apt-get install libssl-dev libffi-dev
之后再继续php install
pip install报错Can't roll back cryptography; was not uninstalled
原文：http://www.cnblogs.com/pcat/p/6817929.html