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Troubleshooting

❝ Where’s the ANY key? ❞
— variously attributed

Diving In

FIXME

Getting to the Command Line

Throughout this book, there are examples of executing Python programs from the command line. Where is the command line?

On Linux, look in your Applications menu for a program called Terminal. (It may be in a submenu like Accessories or System.)

On Mac OS X, there is an application called Terminal in your /Applications/Utilities/ folder. To get there, click on your desktop, open the Go menu, select Go to folder..., and type /Applications/Utilities/. Then double-click the Terminal program.

On Windows, click Start, select Run..., type cmd, and press ENTER.

Running Python on the command line

Once you get to the command line, you should be able to run the Python interactive shell. On the Linux or Mac OS X command line, type python3 and press ENTER. On the Windows command line, type c:\python31\python and press ENTER. If all goes well, you should see something like this:

you@localhost:~$ python3
Python 3.1 (r31:73572, Jul 28 2009, 06:52:23) 
[GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

(Type exit() and press ENTER to exit the Python interactive shell and go back to the command line. This works on all platforms.)

If you get a “command not found” error, it probably means you don’t have Python 3 installed.

you@localhost:~$ python3
bash: python3: command not found

On the other hand, if you get into a Python interactive shell but the version number is not what you expected, you may have more than one version of Python installed. This happens most often on Linux and Mac OS X systems, where an older version of Python is pre-installed. You can install the latest version without deleting the older version (they will live side-by-side in peace), but you will need to be more specific when you run Python from the command line.

For example, on my home Linux box, I have several versions of Python installed so I can test the Python software that I write. To run a specific version, I can type python3.0, python3.1, or python2.6.

mark@atlantis:~$ python3.0
Python 3.0.1+ (r301:69556, Apr 15 2009, 17:25:52)
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()
mark@atlantis:~$ python3.1
Python 3.1 (r31:73572, Jul 28 2009, 06:52:23) 
[GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()
mark@atlantis:~$ python2.6
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

☜ ☞