Installing nova client: PIP Permission Denied even as root
As per this StackOverflow answer, sudo pip install is a rather unsafe practice in that it attempts/allows/intends to modify system Python libraries. In this specific case, the command fails because an install script is attempting to modify the /System/Library/Frameworks/Python.framework directory, which as of macOS 10.11 is guarded by System Integrity Protection. Try using a virtualenv.