Before installing software, back up your computer. While you can't easily burn a DVD of everything on your computer, you can usually burn a DVD of everything in your Mac OS X Home directory.

I've never had a single problem installing Python. I've worked with a number of people, however, who either have bad luck or don't read carefully and have managed to corrupt their Mac OS installation by downloading and installing software. While Python is safe, stable, reliable, virus-free, and well-respected, you may be someone with bad luck who has a problem. A backup is cheap insurance.

You should also have a folder for saving your downloads. You can create a folder in hour Documents called downloads. I suggest that you keep all of your various downloaded tools and utilities in this folder for two reasons. If you need to reinstall your software, you know exactly what you downloaded. When you get a new computer (or an additional computer), you know what needs to be installed on that computer.

Download. After making a backup, go to the www.python.org web site and look for the Download area. In here, you're looking for the pre-built Mac OS X installer. This book will emphasize Python 2.5. In that case, the kit is python-2.5. x -macosx date .dmg. When you click on the filename, your browser should start downloading the file. Save it in your downloads folder.

Backup. Now is a good time to make a second backup. Seriously. It is still cheap insurance.

At this point, you have everything you need to install Python:

When you double-click the python-2.5. x -macosx date .dmg file, it will create a disk image named Universal MacPython 2.5. x . This disk image has your license, a ReadMe file, and the MacPython.mpkg.

When you double-click the MacPython.mpkg fie, it will take all the necessary steps to install Python on your computer. The installer will take you through seven steps. Generally, you'll read the messages and

Introduction. Read the message and click Continue.

Read Me. This is the contents of the ReadMe file on the installer disk image. Read the message and click Continue.

License. You can read the history of Python, and the terms and conditions for using it. To install Python, you must agree with the license. When you click Continue, you will get a pop-up window that asks if you agree. Click Agree to install Python.

Select Destination. Generally, your primary disk drive, usually named Macintosh HD will be highlighted with a green arrow. Click Continue.

Installation Type. If you've done this before, you'll see that this will be an upgrade. If this is the first time, you'll be doing an install. Click the Install or Upgrade button.

You'll be asked for your password. If, for some reason, you aren't the administrator for this computer, you won't be able to install software. Otherwise, provide your password so that you can install software.

Finish Up. The message is usually "The software was successfully installed". Click Close to finish.

In your Applications folder, you'll find a MacPython 2.5 folder, which contains a number of applications.

Look in /System/Library/Frameworks/Python.Framework/Versions for the relevant files. In the bin, Extras and Resources directories you'll find the various applications. The bin/idle file will launch IDLE for us.

Once you've finished installation, you should check to be sure that everything is working correctly.

Python 2.5.1 (r251:54863, Oct  5 2007, 21:08:09) 
[GCC 4.0.1 (Apple Inc. build 5465)] on darwin
Type "copyright", "credits" or "license()" for more information.

    ****************************************************************
    Personal firewall software may warn about the connection IDLE
    makes to its subprocess using this computer's internal loopback
    interface.  This connection is not visible on any external
    interface and no data is sent to or received from the Internet.
    ****************************************************************
    
IDLE 1.2.1      
>>> 

You may notice a Help menu. This has the Python Docs menu item, which you can access through the menu or by hitting F1 . This will launch Safari to show you the Python documents available on the Internet.