Using IDLE

IDLE is free, easy to use, portable, and automatically available on most platforms. I generally recommend it to Python newcomers because it sugarcoats some of the details and does not assume prior experience with system command lines. However, it is somewhat limited compared to more advanced commercial IDEs. To help you avoid some common pitfalls, here is a list of issues that IDLE beginners should bear in mind:

 

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  • You must add “.py” explicitly when saving your files. I mentioned this when talking about files in general, but it’s a common IDLE stumbling block, especially for Windows users. IDLE does not automatically add a .py extension to filenames when files are saved. Be careful to type the .py extension yourself when saving a file for the first time. If you don’t, while you will be able to run your file from IDLE (and system command lines), you will not be able to import it either interactively or from other modules.
  • Run scripts by selecting Run→Run Module in text edit windows, not by interactive imports and reloads. Earlier in this chapter, we saw that it’s possible to run a file by importing it interactively. However, this scheme can grow complex because it requires you to manually reload files after changes. By contrast, using the Run→Run Module menu option in IDLE always runs the most current version of your file, just like running it using a system shell command line. IDLE also prompts you to save your file first, if needed (another common mistake outside IDLE).
  • You need to reload only modules being tested interactively. Like system shell command lines, IDLE’s Run→Run Module menu option always runs the current version of both the top-level file and any modules it imports. Because of this, Run→Run Module eliminates common confusions surrounding imports. You only need to reload modules that you are importing and testing interactively in IDLE. If you choose to use the import and reload technique instead of Run→Run Module, remember that you can use the Alt-P/Alt-N key combinations to recall prior commands.
  • You can customize IDLE. To change the text fonts and colors in IDLE, select the Configure option in the Options menu of any IDLE window. You can also customize key combination actions, indentation settings, and more; see IDLE’s Help pull-down menu for more hints.
  • There is currently no clear-screen option in IDLE. This seems to be a frequent request (perhaps because it’s an option available in similar IDEs), and it might be added eventually. Today, though, there is no way to clear the interactive window’s text. If you want the window’s text to go away, you can either press and hold the Enter key, or type a Python loop to print a series of blank lines (nobody really uses the latter technique, of course, but it sounds more high-tech than pressing the Enter key!).
  • tkinter GUI and threaded programs may not work well with IDLE. Because IDLE is a Python/tkinter program, it can hang if you use it to run certain types of advanced Python/tkinter programs. This has become less of an issue in more recent versions of IDLE that run user code in one process and the IDLE GUI itself in another, but some programs (especially those that use multithreading) might still hang the GUI. Your code may not exhibit such problems, but as a rule of thumb, it’s always safe to use IDLE to edit GUI programs but launch them using other options, such as icon clicks or system command lines. When in doubt, if your code fails in IDLE, try it outside the GUI.
  • If connection errors arise, try starting IDLE in single-process mode. Because IDLE requires communication between its separate user and GUI processes, it can sometimes have trouble starting up on certain platforms (notably, it fails to start occasionally on some Windows machines, due to firewall software that blocks connections). If you run into such connection errors, it’s always possible to start IDLE with a system command line that forces it to run in single-process mode without a user-code subprocess and therefore avoids communication issues: its -n command-line flag forces this mode. On Windows, for example, start a Command Prompt window and run the system command line idle.py -n from within the directory C:\Python30\Lib\idlelib (cd there first if needed).
  • Beware of some IDLE usability features. IDLE does much to make life easier for beginners, but some of its tricks won’t apply outside the IDLE GUI. For instance, IDLE runs your scripts in its own interactive namespace, so variables in your code show up automatically in the IDLE interactive session—you don’t always need to run import commands to access names at the top level of files you’ve already run. This can be handy, but it can also be confusing, because outside the IDLE environment names must always be imported from files to be used.
    IDLE also automatically changes both to the directory of a file just run and adds its directory to the module import search path—a handy feature that allows you to import files there without search path settings, but also something that won’t work the same when you run files outside IDLE. It’s OK to use such features, but don’t forget that they are IDLE behavior, not Python behavior.