How to install Python package with CMake?

How do I upgrade Python on OS X without conflicting with the pre-installed Python binaries and libraries?

• My OS X 10.6.5 comes with Python 2.6.1 pre-installed. However, it is an outdated version of Python and it does not include any external Python libraries, such as the "Image" library for example. I can download a Python 2.7.1 OS X installer from http://python.org (http://www.python.org/ftp/python/2.7.1/python-2.7.1-macosx10.6.dmg). After I install this package, I will have two Python versions on my OS X: The old, pre-installed one, and the new one. How do I keep them separate? Can I remove the old one? When I type 'python' how do I tell it to use the new one? How and where do I install additional Python libraries, since there are two Python versions installed on the system? Unless I take precautions, this seems like a potential for dependency and version conflicts.

• Answer:

  There are three main ways to live with multiple python versions installed. Change the default python interpreter by using python_select which is available from macports sudo port install python27 python_select sudo python_select python27 Note: python_select is actually just setting the link that /opt/local/bin/python points to, so you will need to make sure that /opt/local/bin precedes /usr/bin in your $PATH environment variable. Run a specific python version explicitly by running pythonX.X where X.X is the version number you want to use (presuming it is installed) Keep packages separate using virtualenv which is a bit like a Virtual Machine for python libraries (i.e. a virtual environment).  Google around for an in depth tutorial on how to best use virtualenv as it can be tricky. Finally, as Ash Rust mentions, using libraries that link against non-python C libraries can be a major pain because they tend to link against libraries that are installed outside of the individual python sandboxes (i.e. site-packages) and, for example, MySQLdb might want to link against version 1.4 in a python2.5 version and 2.1 in a python2.6 version (made up example).  For this case it's best to install packages by downloading the eggs and explicitly locating where the relevant library is.  Virtualenv might help out here as well. Myself, I tend to stick with 2) (and put something at the top of a script like #!/usr/bin/python2.7) because it keeps the required configuration with the relevant script instead of the entire system.  1) makes most sense if you're starting with a blank slate of scripts.  I'm getting into 3) as I start to configure deployment scenarios but as of right now I haven't 100% converted.