Install Python 2.7.1 side-by-side with Apple-supplied Python

I have just downloaded the Python 2.7.1 DMG from Python.org. I have seen suggestions to get ActivePython, but I would prefer the one from Python.org.

1. If I just run the mpkg installer inside the DMG, accepting all defaults, will it live peacefully with the Apple-supplied Python?
2. If I type python in Terminal, which one will I get?
3. In Terminal, how do I specify to run the Apple-supplied Python? What about the Python I installed myself?
4. What are these talk about setting the PATH when installing a different Python version? I understand that the Python installer will just set it up automatically. But I still want to peek under the hood. I know how to do this in Windows (Environment Variables). For Mac OS X, how do I tinker with the PATH?

I might as well try these out myself first, but I'm new to the Mac. Python is quite a complicated installation, writing 开发者_运维技巧files to different folders and configuring OS settings like PATH. TrashMe or AppCleaner might not be very effective with uninstalling Python if ever I want to go back to a clean slate. Therefore I want to gain clear insights to my questions above.

If you did not change the default set of packages when using the python.org installer, typing python from a command line should run the newly-installed Python 2.7. (You will need to start a new terminal session after running the installer to see this.) The current python.org installers for OS X create a folder in your Applications directory named Python m.n depending on the Python version. If you look in /Applications/Python 2.7, you'll see a file called Update Shell Profile.command. It's a shell script; you can inspect it in an editor or with Quicklook. Its purpose is to modify the startup files for the most common shell programs on OS X (bash, sh, csh) to ensure that the directory where the new Python's executable commands are located gets added to the front of the list of directories in the PATH environment variable, so that the python commands in it will be found before the Apple-suppled python commands are found. By default, the installer runs the Update Shell Profile.command for you automatically. This should result in something like this:

$ cat ~/.bash_profile
# .bash_profile
# ... other stuff

# Setting PATH for Python 2.7
# The orginal version is saved in .bash_profile.pysave
PATH="/Library/Frameworks/Python.framework/Versions/2.7/bin:${PATH}"
export PATH

If you take a look in that directory, you should see something like this:

$ ls -l /Library/Frameworks/Python.framework/Versions/2.7/bin
total 272
lrwxr-xr-x  1 root  admin      8 Nov 30 00:49 2to3@ -> 2to3-2.7
-rwxrwxr-x  1 root  admin    140 Nov 30 00:30 2to3-2.7*
lrwxr-xr-x  1 root  admin      7 Nov 30 00:49 idle@ -> idle2.7
-rwxrwxr-x  1 root  admin    138 Nov 30 00:30 idle2.7*
lrwxr-xr-x  1 root  admin      8 Nov 30 00:49 pydoc@ -> pydoc2.7
-rwxrwxr-x  1 root  admin    123 Nov 30 00:30 pydoc2.7*
lrwxr-xr-x  1 root  admin      9 Nov 30 00:49 python@ -> python2.7
lrwxr-xr-x  1 root  admin     16 Nov 30 00:49 python-config@ -> python2.7-config
-rwxrwxr-x  1 root  admin  33764 Nov 30 00:31 python2.7*
-rwxrwxr-x  1 root  admin   1663 Nov 30 00:31 python2.7-config*
lrwxr-xr-x  1 root  admin     10 Nov 30 00:49 pythonw@ -> pythonw2.7
-rwxrwxr-x  1 root  admin  33764 Nov 30 00:31 pythonw2.7*
lrwxr-xr-x  1 root  admin     11 Nov 30 00:49 smtpd.py@ -> smtpd2.7.py
-rwxrwxr-x  1 root  admin  18586 Nov 30 00:30 smtpd2.7.py*

The new python is available as the command python2.7 but there is also a symbolic link to it as python. Because the PATH environment has been changed:

$ echo $PATH
/Library/Frameworks/Python.framework/Versions/2.7/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin

when you type python as a command in the shell, that symlink will be found first before the Apple-supplied python in /usr/bin one of the directories where system-supplied user commands are installed (as on OS X 10.6):

$ ls /usr/bin/py*
/usr/bin/pydoc*            /usr/bin/python-config*    /usr/bin/python2.6-config@
/usr/bin/pydoc2.5@         /usr/bin/python2.5@        /usr/bin/pythonw*
/usr/bin/pydoc2.6@         /usr/bin/python2.5-config@ /usr/bin/pythonw2.5@
/usr/bin/python*           /usr/bin/python2.6@        /usr/bin/pythonw2.6@

(Note, in general, you should not attempt to modify or delete files in /usr/bin since they are part of OS X and managed by Apple.)

There are many ways to manage multiple Python installations on OS X; check the archives or the web. One thing to keep in mind is that you can always use an absolute path to the desired python command to check. So with the modified path as above you should see the following behaviors:

$ /Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7 -c 'import sys;print(sys.version)'
2.7.1 (r271:86882M, Nov 30 2010, 09:39:13) 
[GCC 4.0.1 (Apple Inc. build 5494)]
$ python2.7 -c 'import sys;print(sys.version)'
2.7.1 (r271:86882M, Nov 30 2010, 09:39:13) 
[GCC 4.0.1 (Apple Inc. build 5494)]
$ python -c 'import sys;print(sys.version)'
2.7.1 (r271:86882M, Nov 30 2010, 09:39:13) 
[GCC 4.0.1 (Apple Inc. build 5494)]
$ /usr/bin/python -c 'import sys;print(sys.version)'
2.6.1 (r261:67515, Jun 24 2010, 21:47:49) 
[GCC 4.2.1 (Apple Inc. build 5646)]
$ /usr/bin/python2.6 -c 'import sys;print(sys.version)'
2.6.1 (r261:67515, Jun 24 2010, 21:47:49) 
[GCC 4.2.1 (Apple Inc. build 5646)]

1. Yes, it will work fine.
2. You will have to change the appropriate symlink. You can always check using which python.
3. You can create extra symlinks for the different versions (e.g. python_mac and python_standard).
4. Read this.

Different python installations can be made to run without hinderance specially, if you use virtualenv

You can follow these article about

1. bootstrapping virtual environments
2. setting up python ecosystems

These will instruct you on installing different versions of python in different places each with their own set of site-packages and have them individually work on different projects. Highly recommend you look into it as it also explains how to change the PATH variable in an easy way so that different python installations can be found by your shell commands.

Here is some quick info about where different python installations go to..

Typing which python at the terminal will tell you its location. You can also use python -V to see the version used. Remember, python and python2.x can be different things. You can assign appropriate names to different python installations in order to call them at the terminal or in your scripts by using alias command. For instance,

alias /Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7 sys-py27

• Apple supplied system python is installed at /System/Library/Frameworks/Python.framework and /usr/bin/python

  • Indeed, you shouldn't mess with these by trying to delete them manually. The system python could be in use by other software in your computer.

  • To check what is currently the system python you can use

    python -c 'import sys;print(sys.version)'

• Packaged installers that you download and run typically install to /Library/Frameworks/Python.framework/Versions/2.7/bin/

  • You can manually remove the Python.framework folder. You might also see Python in the Applications folder along with other things like IDLE, AppBuilder and PythonLauncher. You can just go ahead and delete those if you need to.

• MacPorts will install python or something like python26 and python27 to /opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin/

  • You can uninstall them by using usual sudo port uninstall packageName and if you want to remove dependencies use something like this code

    sudo port uninstall python27 --follow-dependents installed

  • All additional things like numpy, scipy, PIL, opencv, etc. that you try to install using port will go to

    /opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages