/usr/bin/python vs /opt/local/bin/python2.7 on OS X

Question

Can you shed some light on the interaction between the Python interpreter distributed with OS X and the one that can be installed through MacPorts?

While installing networkx and matplotlib I am having difficulties with the interaction of /usr/bin/python and /opt/local/bin/python2.7. (The latter is itself a soft pointer to /opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7)

How can I be certain which Python, pip, and Python libraries I am using at any one time?

More importantly, it appears that installing matplotlib is not possible on Lion. It fails with Requires numpy 1.6 or later to build. (Found 1.5.1). If I upgrade by running sudo pip install --upgrade numpy, it does not help. Subsequently attempting to install matplotlib (sudo /usr/local/bin/pip install matplotlib) still fails with the same (Requires numpy 1.6...) message. How can I install matplotlib?

Answer 1

Points to keep in mind about Python

• If a script foobar.py starts with #!/usr/bin/env python, then you will always get the OS X Python. That's the case even though MacPorts puts /opt/local/bin ahead of /usr/bin in your path. The reason is that MacPorts uses the name python2.7. If you want to use env and yet use MacPorts Python, you have to write #!/usr/bin/env python2.7.
• If a script foobar.py starts explicitly with #!/usr/bin/python or with #!/opt/local/bin/python2.7, then the corresponding Python interpreter will be used.

What to keep in mind about pip

• To install pip for /usr/bin/python, you need to run sudo /usr/bin/easy_install pip. You then call pip (which will not be installed by easy_install in /usr/bin/pip, but rather in /usr/local/bin/pip)
• To install pip for /opt/local/bin/python2.7, you need to run sudo port install py27-pip. You would then call pip-2.7. You will get the pip in /opt/local/bin. Be careful, because if you type pip2.7 you will get /usr/local/bin/pip2.7 (the OS X pip).

Installing networkx and matplotlib

• To install networkx for the OS X Python you would run sudo /usr/local/bin/pip install networkx. I don't know how to install matplotlib on OS X Lion. It may be that OS X has to stick to numpy 1.5.1 because it uses it internally.
• To install networkx and matplotlib for MacPorts-Python, call sudo pip-2.7 install networkx and sudo pip-2.7 install matplotlib. matplotlib installs with a lot of warnings, but it passes.