Fixing gevent Installation Errors on OS X 10.11
A fix for gevent installation failures on OS X 10.11 caused by the protected system Python and bundled six package.
On OS X 10.11, installing gevent directly with pip failed.
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I found several possible fixes on Stack Overflow, but they all failed because six 1.4.1 could not be uninstalled. The operating system ships that version with its framework-based Python installation. System Integrity Protection prevents it from being removed, even by the root user.
The simplest solution is to install and use your own Python. Other approaches are discussed in this pip issue.
brew install python