4. Using Python on a Macintosh

Author:Bob Savage <bobsavage@mac.com>

Python on a Macintosh running Mac OS X is in principle very similar to Python on any other Unix platform, but there are a number of additional features such as the IDE and the Package Manager that are worth pointing out.

4.1. Getting and Installing MacPython

Mac OS X 10.5 comes with Python 2.5.1 pre-installed by Apple. If you wish, you are invited to install the most recent version of Python from the Python website (http://www.python.org). A current “universal binary” build of Python, which runs natively on the Mac’s new Intel and legacy PPC CPU’s, is available there.

What you get after installing is a number of things:

• A MacPython 2.5 folder in your Applications folder. In here you find IDLE, the development environment that is a standard part of official Python distributions; PythonLauncher, which handles double-clicking Python scripts from the Finder; and the “Build Applet” tool, which allows you to package Python scripts as standalone applications on your system.
• A framework /Library/Frameworks/Python.framework, which includes the Python executable and libraries. The installer adds this location to your shell path. To uninstall MacPython, you can simply remove these three things. A symlink to the Python executable is placed in /usr/local/bin/.

The Apple-provided build of Python is installed in /System/Library/Frameworks/Python.framework and /usr/bin/python, respectively. You should never modify or delete these, as they are Apple-controlled and are used by Apple- or third-party software. Remember that if you choose to install a newer Python version from python.org, you will have two different but functional Python installations on your computer, so it will be important that your paths and usages are consistent with what you want to do.

IDLE includes a help menu that allows you to access Python documentation. If you are completely new to Python you should start reading the tutorial introduction in that document.

If you are familiar with Python on other Unix platforms you should read the section on running Python scripts from the Unix shell.

4.1.1. How to run a Python script

Your best way to get started with Python on Mac OS X is through the IDLE integrated development environment, see section The IDE and use the Help menu when the IDE is running.

If you want to run Python scripts from the Terminal window command line or from the Finder you first need an editor to create your script. Mac OS X comes with a number of standard Unix command line editors, vim and emacs among them. If you want a more Mac-like editor, BBEdit or TextWrangler from Bare Bones Software (see http://www.barebones.com/products/bbedit/index.shtml) are good choices, as is TextMate (see http://macromates.com/). Other editors include Gvim (http://macvim.org) and Aquamacs (http://aquamacs.org/).

To run your script from the Terminal window you must make sure that /usr/local/bin is in your shell search path.

To run your script from the Finder you have two options:

• Drag it to PythonLauncher
• Select PythonLauncher as the default application to open your script (or any .py script) through the finder Info window and double-click it. PythonLauncher has various preferences to control how your script is launched. Option-dragging allows you to change these for one invocation, or use its Preferences menu to change things globally.

4.1.2. Running scripts with a GUI

With older versions of Python, there is one Mac OS X quirk that you need to be aware of: programs that talk to the Aqua window manager (in other words, anything that has a GUI) need to be run in a special way. Use pythonw instead of python to start such scripts.

With Python 2.5, you can use either python or pythonw.

4.1.3. Configuration

Python on OS X honors all standard Unix environment variables such as PYTHONPATH, but setting these variables for programs started from the Finder is non-standard as the Finder does not read your .profile or .cshrc at startup. You need to create a file ~ /.MacOSX/environment.plist. See Apple’s Technical Document QA1067 for details.

For more information on installation Python packages in MacPython, see section Installing Additional Python Packages.

4.2. The IDE

MacPython ships with the standard IDLE development environment. A good introduction to using IDLE can be found at http://hkn.eecs.berkeley.edu/~dyoo/python/idle_intro/index.html.

4.3. Installing Additional Python Packages

There are several methods to install additional Python packages:

• http://pythonmac.org/packages/ contains selected compiled packages for Python 2.5, 2.4, and 2.3.
• Packages can be installed via the standard Python distutils mode (python setup.py install).
• Many packages can also be installed via the setuptools extension.

4.4. GUI Programming on the Mac

There are several options for building GUI applications on the Mac with Python.

PyObjC is a Python binding to Apple’s Objective-C/Cocoa framework, which is the foundation of most modern Mac development. Information on PyObjC is available from http://pyobjc.sourceforge.net.

The standard Python GUI toolkit is tkinter, based on the cross-platform Tk toolkit (http://www.tcl.tk). An Aqua-native version of Tk is bundled with OS X by Apple, and the latest version can be downloaded and installed from http://www.activestate.com; it can also be built from source.

wxPython is another popular cross-platform GUI toolkit that runs natively on Mac OS X. Packages and documentation are available from http://www.wxpython.org.

PyQt is another popular cross-platform GUI toolkit that runs natively on Mac OS X. More information can be found at http://www.riverbankcomputing.co.uk/software/pyqt/intro.

4.5. Distributing Python Applications on the Mac

The “Build Applet” tool that is placed in the MacPython 2.5 folder is fine for packaging small Python scripts on your own machine to run as a standard Mac application. This tool, however, is not robust enough to distribute Python applications to other users.

The standard tool for deploying standalone Python applications on the Mac is py2app. More information on installing and using py2app can be found at http://undefined.org/python/#py2app.

4.6. Application Scripting

Python can also be used to script other Mac applications via Apple’s Open Scripting Architecture (OSA); see http://appscript.sourceforge.net. Appscript is a high-level, user-friendly Apple event bridge that allows you to control scriptable Mac OS X applications using ordinary Python scripts. Appscript makes Python a serious alternative to Apple’s own AppleScript language for automating your Mac. A related package, PyOSA, is an OSA language component for the Python scripting language, allowing Python code to be executed by any OSA-enabled application (Script Editor, Mail, iTunes, etc.). PyOSA makes Python a full peer to AppleScript.

4.7. Other Resources

The MacPython mailing list is an excellent support resource for Python users and developers on the Mac:

http://www.python.org/community/sigs/current/pythonmac-sig/

Another useful resource is the MacPython wiki:

http://wiki.python.org/moin/MacPython