Python Idle


Release Date: June 27, 2018

Python 3.6.6 was the sixth maintenance release of Python 3.6.

There are now newer security-fix releases of Python 3.6 that supersede 3.6.6 and Python 3.8 is now the latest feature release of Python 3. Get the latest releases of 3.6.x and 3.8.x here. Python 3.6.8 is planned to be the last bugfix releasefor 3.6.x. Following the release of 3.6.8, we plan to provide security fixes for Python 3.6 as needed through 2021, five years following its initial release.

Among the new major new features in Python 3.6 were:

Note that Python 3.6.10 cannot be used on Windows XP or earlier. No files for this release. Python 3.5.9 - Nov. Note that Python 3.5.9 cannot be used on Windows XP or earlier. No files for this release. Python 3.5.8 - Oct. Note that Python 3.5.8 cannot be used on Windows XP or earlier. No files for this release. Information on tools for unpacking archive files provided on is available. Tip: even if you download a ready-made binary for your platform, it makes sense to also download the source. This lets you browse the standard library (the subdirectory Lib ) and the standard collections of demos ( Demo ) and tools ( Tools ) that come with it.

  • PEP 468, Preserving Keyword Argument Order
  • PEP 487, Simpler customization of class creation
  • PEP 495, Local Time Disambiguation
  • PEP 498, Literal String Formatting
  • PEP 506, Adding A Secrets Module To The Standard Library
  • PEP 509, Add a private version to dict
  • PEP 515, Underscores in Numeric Literals
  • PEP 519, Adding a file system path protocol
  • PEP 520, Preserving Class Attribute Definition Order
  • PEP 523, Adding a frame evaluation API to CPython
  • PEP 524, Make os.urandom() blocking on Linux (during system startup)
  • PEP 525, Asynchronous Generators (provisional)
  • PEP 526, Syntax for Variable Annotations (provisional)
  • PEP 528, Change Windows console encoding to UTF-8
  • PEP 529, Change Windows filesystem encoding to UTF-8
  • PEP 530, Asynchronous Comprehensions

Please see What’s New In Python 3.6 for more information.

  • PEP 494, 3.6 Release Schedule
  • Report bugs at
  • Help fund Python and its community.
  • The binaries for AMD64 will also work on processors that implement the Intel 64 architecture. (Also known as the 'x64' architecture, and formerly known as both 'EM64T' and 'x86-64'.)
  • If installing Python 3.6 as a non-privileged user, you may need to escalate to administrator privileges to install an update to your C runtime libraries.
  • There are now 'web-based' installers for Windows platforms; the installer will download the needed software components at installation time.
  • There are redistributable zip files containing the Windows builds, making it easy to redistribute Python as part of another software package. Please see the documentation regarding Embedded Distribution for more information.
  • NEW as of 3.6.5: we are providing two binary installer options for download. The new variant works on macOS 10.9 (Mavericks) and later systems and comes with its own batteries-included version oF Tcl/Tk 8.6 for users of IDLE and other tkinter-based GUI applications. It is 64-bit only as Apple is deprecating 32-bit support in future macOS releases. For 3.6.5+, the 10.9+ variant is offered as an additional more modern alternative to the traditional 10.6+ variant in earlier 3.6.x releases. The 10.6+ variant still requires installing a third-party version of Tcl/Tk 8.5. If you are using macOS 10.9 or later, consider using the new installer variant, unless you are building Python applications that also need to work on older macOS systems. Binary extension modules (including wheels) built for earlier versions of 3.6.x with the 10.6 variant should continue to work with either 3.6.6 variant without recompilation.
  • Both installer variants include private copies of OpenSSL 1.0.2. Please carefully read the Important Information displayed during installation for information about SSL/TLS certificate validation and the Install Certificates.command.
VersionOperating SystemDescriptionMD5 SumFile SizeGPG
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XZ compressed source tarballSource releasec3f30a0aff425dda77d19e02f420d6ba17156744SIG
macOS 64-bit/32-bit installerMac OS Xfor Mac OS X 10.6 and laterc58267cab96f6d291d332a2b163edd3328060853SIG
macOS 64-bit installerMac OS Xfor OS X 10.9 and later3ad13cc51c488182ed21a50050a38ba726954940SIG
Windows help fileWindowse01b52e24494611121b4a866932b41238139973SIG
Windows x86-64 embeddable zip fileWindowsfor AMD64/EM64T/x647148ec14edfdc13f42e06a14d617c9217186734SIG
Windows x86-64 executable installerWindowsfor AMD64/EM64T/x64767db14ed07b245e24e10785f9d28e2931930528SIG
Windows x86-64 web-based installerWindowsfor AMD64/EM64T/x64f30be4659721a0ef68e29cae099fed6f1319992SIG
Windows x86 embeddable zip fileWindowsb4c424de065bad238c71359f3cd71ef26401894SIG
Windows x86 executable installerWindows467161f1e894254096f9a69e2db3302c30878752SIG
Windows x86 web-based installerWindowsa940f770b4bc617ab4a308ff1e27abd61293456SIG

Source code:Lib/idlelib/

IDLE is Python’s Integrated Development and Learning Environment.

IDLE has the following features:

  • coded in 100% pure Python, using the tkinter GUI toolkit

  • cross-platform: works mostly the same on Windows, Unix, and macOS

  • Python shell window (interactive interpreter) with colorizingof code input, output, and error messages

  • multi-window text editor with multiple undo, Python colorizing,smart indent, call tips, auto completion, and other features

  • search within any window, replace within editor windows, and searchthrough multiple files (grep)

  • debugger with persistent breakpoints, stepping, and viewingof global and local namespaces

  • configuration, browsers, and other dialogs


IDLE has two main window types, the Shell window and the Editor window. It ispossible to have multiple editor windows simultaneously. On Windows andLinux, each has its own top menu. Each menu documented below indicateswhich window type it is associated with.

Output windows, such as used for Edit => Find in Files, are a subtype of editorwindow. They currently have the same top menu but a differentdefault title and context menu.

On macOS, there is one application menu. It dynamically changes accordingto the window currently selected. It has an IDLE menu, and some entriesdescribed below are moved around to conform to Apple guidelines.

File menu (Shell and Editor)¶

New File

Create a new file editing window.


Open an existing file with an Open dialog.

Recent Files

Open a list of recent files. Click one to open it.

Open Module…

Open an existing module (searches sys.path).

Class Browser

Show functions, classes, and methods in the current Editor file in atree structure. In the shell, open a module first.

Path Browser

Show sys.path directories, modules, functions, classes and methods in atree structure.


Save the current window to the associated file, if there is one. Windowsthat have been changed since being opened or last saved have a * beforeand after the window title. If there is no associated file,do Save As instead.

Save As…

Save the current window with a Save As dialog. The file saved becomes thenew associated file for the window.

Save Copy As…

Save the current window to different file without changing the associatedfile.

Print Window

Print the current window to the default printer.


Close the current window (ask to save if unsaved).


Close all windows and quit IDLE (ask to save unsaved windows).

Edit menu (Shell and Editor)¶


Undo the last change to the current window. A maximum of 1000 changes maybe undone.


Redo the last undone change to the current window.


Copy selection into the system-wide clipboard; then delete the selection.


Copy selection into the system-wide clipboard.


Insert contents of the system-wide clipboard into the current window.

The clipboard functions are also available in context menus.

Select All

Select the entire contents of the current window.


Open a search dialog with many options

Find Again

Repeat the last search, if there is one.

Find Selection

Search for the currently selected string, if there is one.

Find in Files…

Open a file search dialog. Put results in a new output window.


Open a search-and-replace dialog.

Go to Line

Move the cursor to the beginning of the line requested and make thatline visible. A request past the end of the file goes to the end.Clear any selection and update the line and column status.

Show Completions

Open a scrollable list allowing selection of existing names. SeeCompletions in the Editing and navigation section below.

Expand Word

Expand a prefix you have typed to match a full word in the same window;repeat to get a different expansion.

Show call tip

After an unclosed parenthesis for a function, open a small window withfunction parameter hints. See Calltips in theEditing and navigation section below.

Show surrounding parens

Highlight the surrounding parenthesis.

Format menu (Editor window only)¶

Indent Region

Shift selected lines right by the indent width (default 4 spaces).

Dedent Region

Shift selected lines left by the indent width (default 4 spaces).

Comment Out Region

Insert ## in front of selected lines.

Uncomment Region

Remove leading # or ## from selected lines.

Tabify Region

Turn leading stretches of spaces into tabs. (Note: We recommend using4 space blocks to indent Python code.)

Untabify Region

Turn all tabs into the correct number of spaces.

Toggle Tabs

Open a dialog to switch between indenting with spaces and tabs.

New Indent Width

Open a dialog to change indent width. The accepted default by the Pythoncommunity is 4 spaces.

Format Paragraph

Reformat the current blank-line-delimited paragraph in comment block ormultiline string or selected line in a string. All lines in theparagraph will be formatted to less than N columns, where N defaults to 72.

Strip trailing whitespace

Remove trailing space and other whitespace characters after the lastnon-whitespace character of a line by applying str.rstrip to each line,including lines within multiline strings. Except for Shell windows,remove extra newlines at the end of the file.

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Run menu (Editor window only)¶

Run Module

Do Check Module. If no error, restart the shell to clean theenvironment, then execute the module. Output is displayed in the Shellwindow. Note that output requires use of print or write.When execution is complete, the Shell retains focus and displays a prompt.At this point, one may interactively explore the result of execution.This is similar to executing a file with python-ifile at a commandline.

Run… Customized

Same as Run Module, but run the module with customizedsettings. Command Line Arguments extend sys.argv as if passedon a command line. The module can be run in the Shell without restarting.

Check Module

Check the syntax of the module currently open in the Editor window. If themodule has not been saved IDLE will either prompt the user to save orautosave, as selected in the General tab of the Idle Settings dialog. Ifthere is a syntax error, the approximate location is indicated in theEditor window.

Python Shell

Open or wake up the Python Shell window.

Shell menu (Shell window only)¶

View Last Restart

Scroll the shell window to the last Shell restart.

Restart Shell

Restart the shell to clean the environment and reset display and exception handling.

Previous History

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Cycle through earlier commands in history which match the current entry.

Next History

Cycle through later commands in history which match the current entry.

Interrupt Execution

Stop a running program.

Debug menu (Shell window only)¶

Go to File/Line

Look on the current line. with the cursor, and the line above for a filenameand line number. If found, open the file if not already open, and show theline. Use this to view source lines referenced in an exception tracebackand lines found by Find in Files. Also available in the context menu ofthe Shell window and Output windows.

Debugger (toggle)

When activated, code entered in the Shell or run from an Editor will rununder the debugger. In the Editor, breakpoints can be set with the contextmenu. This feature is still incomplete and somewhat experimental.

Stack Viewer

Show the stack traceback of the last exception in a tree widget, withaccess to locals and globals.

Auto-open Stack Viewer

Toggle automatically opening the stack viewer on an unhandled exception.

Options menu (Shell and Editor)¶

Configure IDLE

Open a configuration dialog and change preferences for the following:fonts, indentation, keybindings, text color themes, startup windows andsize, additional help sources, and extensions. On macOS, open theconfiguration dialog by selecting Preferences in the applicationmenu. For more details, seeSetting preferences under Help and preferences.

Most configuration options apply to all windows or all future windows.The option items below only apply to the active window.

Show/Hide Code Context (Editor Window only)

Open a pane at the top of the edit window which shows the block contextof the code which has scrolled above the top of the window. SeeCode Context in the Editing and Navigation sectionbelow.

Show/Hide Line Numbers (Editor Window only)

Open a column to the left of the edit window which shows the numberof each line of text. The default is off, which may be changed in thepreferences (see Setting preferences).

Zoom/Restore Height

Toggles the window between normal size and maximum height. The initial sizedefaults to 40 lines by 80 chars unless changed on the General tab of theConfigure IDLE dialog. The maximum height for a screen is determined bymomentarily maximizing a window the first time one is zoomed on the screen.Changing screen settings may invalidate the saved height. This toggle hasno effect when a window is maximized.

Window menu (Shell and Editor)¶

Lists the names of all open windows; select one to bring it to the foreground(deiconifying it if necessary).

Help menu (Shell and Editor)¶

About IDLE

Display version, copyright, license, credits, and more.


Display this IDLE document, detailing the menu options, basic editing andnavigation, and other tips.

Python Docs

Access local Python documentation, if installed, or start a web browserand open showing the latest Python documentation.

Turtle Demo

Run the turtledemo module with example Python code and turtle drawings.

Additional help sources may be added here with the Configure IDLE dialog underthe General tab. See the Help sources subsection belowfor more on Help menu choices.

Context Menus¶

Open a context menu by right-clicking in a window (Control-click on macOS).Context menus have the standard clipboard functions also on the Edit menu.


Copy selection into the system-wide clipboard; then delete the selection.


Copy selection into the system-wide clipboard.


Insert contents of the system-wide clipboard into the current window.

Editor windows also have breakpoint functions. Lines with a breakpoint set arespecially marked. Breakpoints only have an effect when running under thedebugger. Breakpoints for a file are saved in the user’s .idlercdirectory.

Set Breakpoint

Set a breakpoint on the current line.

Clear Breakpoint

Clear the breakpoint on that line.

Shell and Output windows also have the following.

Go to file/line

Same as in Debug menu.

The Shell window also has an output squeezing facility explained in the PythonShell window subsection below.


If the cursor is over an output line, squeeze all the output betweenthe code above and the prompt below down to a ‘Squeezed text’ label.

Editing and navigation¶

Editor windows¶

IDLE may open editor windows when it starts, depending on settingsand how you start IDLE. Thereafter, use the File menu. There can be onlyone open editor window for a given file.

The title bar contains the name of the file, the full path, and the versionof Python and IDLE running the window. The status bar contains the linenumber (‘Ln’) and column number (‘Col’). Line numbers start with 1;column numbers with 0.

Python Idle Online

IDLE assumes that files with a known .py* extension contain Python codeand that other files do not. Run Python code with the Run menu.

Key bindings¶

In this section, ‘C’ refers to the Control key on Windows and Unix andthe Command key on macOS.

  • Backspace deletes to the left; Del deletes to the right

  • C-Backspace delete word left; C-Del delete word to the right

  • Arrow keys and Page Up/Page Down to move around

  • C-LeftArrow and C-RightArrow moves by words

  • Home/End go to begin/end of line

  • C-Home/C-End go to begin/end of file

  • Some useful Emacs bindings are inherited from Tcl/Tk:

    • C-a beginning of line

    • C-e end of line

    • C-k kill line (but doesn’t put it in clipboard)

    • C-l center window around the insertion point

    • C-b go backward one character without deleting (usually you canalso use the cursor key for this)

    • C-f go forward one character without deleting (usually you canalso use the cursor key for this)

    • C-p go up one line (usually you can also use the cursor key forthis)

    • C-d delete next character

Standard keybindings (like C-c to copy and C-v to paste)may work. Keybindings are selected in the Configure IDLE dialog.

Automatic indentation¶

After a block-opening statement, the next line is indented by 4 spaces (in thePython Shell window by one tab). After certain keywords (break, return etc.)the next line is dedented. In leading indentation, Backspace deletes upto 4 spaces if they are there. Tab inserts spaces (in the PythonShell window one tab), number depends on Indent width. Currently, tabsare restricted to four spaces due to Tcl/Tk limitations.

See also the indent/dedent region commands on theFormat menu.


Completions are supplied, when requested and available, for modulenames, attributes of classes or functions, or filenames. Each requestmethod displays a completion box with existing names. (See tabcompletions below for an exception.) For any box, change the namebeing completed and the item highlighted in the box bytyping and deleting characters; by hitting Up, Down,PageUp, PageDown, Home, and End keys;and by a single click within the box. Close the box with Escape,Enter, and double Tab keys or clicks outside the box.A double click within the box selects and closes.

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One way to open a box is to type a key character and wait for apredefined interval. This defaults to 2 seconds; customize itin the settings dialog. (To prevent auto popups, set the delay to alarge number of milliseconds, such as 100000000.) For imported modulenames or class or function attributes, type ‘.’.For filenames in the root directory, type os.sep oros.altsep immediately after an opening quote. (On Windows,one can specify a drive first.) Move into subdirectories by typing adirectory name and a separator.

Instead of waiting, or after a box is closed, open a completion boximmediately with Show Completions on the Edit menu. The default hotkey is C-space. If one types a prefix for the desired namebefore opening the box, the first match or near miss is made visible.The result is the same as if one enters a prefixafter the box is displayed. Show Completions after a quote completesfilenames in the current directory instead of a root directory.

Hitting Tab after a prefix usually has the same effect as ShowCompletions. (With no prefix, it indents.) However, if there is onlyone match to the prefix, that match is immediately added to the editortext without opening a box.

Invoking ‘Show Completions’, or hitting Tab after a prefix,outside of a string and without a preceding ‘.’ opens a box withkeywords, builtin names, and available module-level names.

When editing code in an editor (as oppose to Shell), increase theavailable module-level names by running your codeand not restarting the Shell thereafter. This is especially usefulafter adding imports at the top of a file. This also increasespossible attribute completions.

Completion boxes intially exclude names beginning with ‘_’ or, formodules, not included in ‘__all__’. The hidden names can be accessedby typing ‘_’ after ‘.’, either before or after the box is opened.

Python Idle Shell


A calltip is shown automatically when one types ( after the nameof an accessible function. A function name expression may includedots and subscripts. A calltip remains until it is clicked, the cursoris moved out of the argument area, or ) is typed. Whenever thecursor is in the argument part of a definition, select Edit and “ShowCall Tip” on the menu or enter its shortcut to display a calltip.

The calltip consists of the function’s signature and docstring up tothe latter’s first blank line or the fifth non-blank line. (Some builtinfunctions lack an accessible signature.) A ‘/’ or ‘*’ in the signatureindicates that the preceding or following arguments are passed byposition or name (keyword) only. Details are subject to change.

In Shell, the accessible functions depends on what modules have beenimported into the user process, including those imported by Idle itself,and which definitions have been run, all since the last restart.

For example, restart the Shell and enter itertools.count(. A calltipappears because Idle imports itertools into the user process for its ownuse. (This could change.) Enter turtle.write( and nothing appears.Idle does not itself import turtle. The menu entry and shortcut also donothing. Enter importturtle. Thereafter, turtle.write(will display a calltip.

In an editor, import statements have no effect until one runs the file.One might want to run a file after writing import statements, afteradding function definitions, or after opening an existing file.

Code Context¶

Within an editor window containing Python code, code context can be toggledin order to show or hide a pane at the top of the window. When shown, thispane freezes the opening lines for block code, such as those beginning withclass, def, or if keywords, that would have otherwise scrolledout of view. The size of the pane will be expanded and contracted as neededto show the all current levels of context, up to the maximum number oflines defined in the Configure IDLE dialog (which defaults to 15). If thereare no current context lines and the feature is toggled on, a single blankline will display. Clicking on a line in the context pane will move thatline to the top of the editor.

The text and background colors for the context pane can be configured underthe Highlights tab in the Configure IDLE dialog.

Python Shell window¶

With IDLE’s Shell, one enters, edits, and recalls complete statements.Most consoles and terminals only work with a single physical line at a time.

When one pastes code into Shell, it is not compiled and possibly executeduntil one hits Return. One may edit pasted code first.If one pastes more that one statement into Shell, the result will be aSyntaxError when multiple statements are compiled as if they were one.

The editing features described in previous subsections work when enteringcode interactively. IDLE’s Shell window also responds to the following keys.

  • C-c interrupts executing command

  • C-d sends end-of-file; closes window if typed at a >>> prompt

  • Alt-/ (Expand word) is also useful to reduce typing

    Command history

    • Alt-p retrieves previous command matching what you have typed. OnmacOS use C-p.

    • Alt-n retrieves next. On macOS use C-n.

    • Return while on any previous command retrieves that command

Text colors¶

Idle defaults to black on white text, but colors text with special meanings.For the shell, these are shell output, shell error, user output, anduser error. For Python code, at the shell prompt or in an editor, these arekeywords, builtin class and function names, names following class anddef, strings, and comments. For any text window, these are the cursor (whenpresent), found text (when possible), and selected text.

Text coloring is done in the background, so uncolorized text is occasionallyvisible. To change the color scheme, use the Configure IDLE dialogHighlighting tab. The marking of debugger breakpoint lines in the editor andtext in popups and dialogs is not user-configurable.

Startup and code execution¶

Upon startup with the -s option, IDLE will execute the file referenced bythe environment variables IDLESTARTUP or PYTHONSTARTUP.IDLE first checks for IDLESTARTUP; if IDLESTARTUP is present the filereferenced is run. If IDLESTARTUP is not present, IDLE checks forPYTHONSTARTUP. Files referenced by these environment variables areconvenient places to store functions that are used frequently from the IDLEshell, or for executing import statements to import common modules.

In addition, Tk also loads a startup file if it is present. Note that theTk file is loaded unconditionally. This additional file is and islooked for in the user’s home directory. Statements in this file will beexecuted in the Tk namespace, so this file is not useful for importingfunctions to be used from IDLE’s Python shell.

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Command line usage¶

If there are arguments:

  • If -, -c, or r is used, all arguments are placed insys.argv[1:..] and sys.argv[0] is set to ', '-c',or '-r'. No editor window is opened, even if that is the defaultset in the Options dialog.

  • Otherwise, arguments are files opened for editing andsys.argv reflects the arguments passed to IDLE itself.

Startup failure¶

IDLE uses a socket to communicate between the IDLE GUI process and the usercode execution process. A connection must be established whenever the Shellstarts or restarts. (The latter is indicated by a divider line that says‘RESTART’). If the user process fails to connect to the GUI process, itusually displays a Tk error box with a ‘cannot connect’ messagethat directs the user here. It then exits.

One specific connection failure on Unix systems results frommisconfigured masquerading rules somewhere in a system’s network setup.When IDLE is started from a terminal, one will see a message startingwith **Invalidhost:.The valid value is can diagnose with tcpconnect-irv127.0.0.16543 in oneterminal window and tcplisten<sameargs> in another.

A common cause of failure is a user-written file with the same name as astandard library module, such as and When such afile is located in the same directory as a file that is about to be run,IDLE cannot import the stdlib file. The current fix is to rename theuser file.

Though less common than in the past, an antivirus or firewall program maystop the connection. If the program cannot be taught to allow theconnection, then it must be turned off for IDLE to work. It is safe toallow this internal connection because no data is visible on externalports. A similar problem is a network mis-configuration that blocksconnections.

Python installation issues occasionally stop IDLE: multiple versions canclash, or a single installation might need admin access. If one undo theclash, or cannot or does not want to run as admin, it might be easiest tocompletely remove Python and start over.

A zombie pythonw.exe process could be a problem. On Windows, use TaskManager to check for one and stop it if there is. Sometimes a restartinitiated by a program crash or Keyboard Interrupt (control-C) may failto connect. Dismissing the error box or using Restart Shell on the Shellmenu may fix a temporary problem.

When IDLE first starts, it attempts to read user configuration files in~/.idlerc/ (~ is one’s home directory). If there is a problem, an errormessage should be displayed. Leaving aside random disk glitches, this canbe prevented by never editing the files by hand. Instead, use theconfiguration dialog, under Options. Once there is an error in a userconfiguration file, the best solution may be to delete it and start overwith the settings dialog.

If IDLE quits with no message, and it was not started from a console, trystarting it from a console or terminal (python-midlelib) and see ifthis results in an error message.

On Unix-based systems with tcl/tk older than 8.6.11 (seeAboutIDLE) certain characters of certain fonts can causea tk failure with a message to the terminal. This can happen eitherif one starts IDLE to edit a file with such a character or laterwhen entering such a character. If one cannot upgrade tcl/tk,then re-configure IDLE to use a font that works better.

Running user code¶

With rare exceptions, the result of executing Python code with IDLE isintended to be the same as executing the same code by the default method,directly with Python in a text-mode system console or terminal window.However, the different interface and operation occasionally affectvisible results. For instance, sys.modules starts with more entries,and threading.active_count() returns 2 instead of 1.

By default, IDLE runs user code in a separate OS process rather than inthe user interface process that runs the shell and editor. In the executionprocess, it replaces sys.stdin, sys.stdout, and sys.stderrwith objects that get input from and send output to the Shell window.The original values stored in sys.__stdin__, sys.__stdout__, andsys.__stderr__ are not touched, but may be None.

Sending print output from one process to a text widget in another isslower than printing to a system terminal in the same process.This has the most effect when printing multiple arguments, as the stringfor each argument, each separator, the newline are sent separately.For development, this is usually not a problem, but if one wants toprint faster in IDLE, format and join together everything one wantsdisplayed together and then print a single string. Both format stringsand str.join() can help combine fields and lines.

IDLE’s standard stream replacements are not inherited by subprocessescreated in the execution process, whether directly by user code or bymodules such as multiprocessing. If such subprocess use input fromsys.stdin or print or write to sys.stdout or sys.stderr,IDLE should be started in a command line window. The secondary subprocesswill then be attached to that window for input and output.

If sys is reset by user code, such as with importlib.reload(sys),IDLE’s changes are lost and input from the keyboard and output to the screenwill not work correctly.

When Shell has the focus, it controls the keyboard and screen. This isnormally transparent, but functions that directly access the keyboardand screen will not work. These include system-specific functions thatdetermine whether a key has been pressed and if so, which.

The IDLE code running in the execution process adds frames to the call stackthat would not be there otherwise. IDLE wraps sys.getrecursionlimit andsys.setrecursionlimit to reduce the effect of the additional stackframes.

When user code raises SystemExit either directly or by calling sys.exit,IDLE returns to a Shell prompt instead of exiting.

User output in Shell¶

When a program outputs text, the result is determined by thecorresponding output device. When IDLE executes user code, sys.stdoutand sys.stderr are connected to the display area of IDLE’s Shell. Some ofits features are inherited from the underlying Tk Text widget. Othersare programmed additions. Where it matters, Shell is designed for developmentrather than production runs.

For instance, Shell never throws away output. A program that sends unlimitedoutput to Shell will eventually fill memory, resulting in a memory error.In contrast, some system text windows only keep the last n lines of output.A Windows console, for instance, keeps a user-settable 1 to 9999 lines,with 300 the default.

A Tk Text widget, and hence IDLE’s Shell, displays characters (codepoints) inthe BMP (Basic Multilingual Plane) subset of Unicode. Which characters aredisplayed with a proper glyph and which with a replacement box depends on theoperating system and installed fonts. Tab characters cause the following textto begin after the next tab stop. (They occur every 8 ‘characters’). Newlinecharacters cause following text to appear on a new line. Other controlcharacters are ignored or displayed as a space, box, or something else,depending on the operating system and font. (Moving the text cursor throughsuch output with arrow keys may exhibit some surprising spacing behavior.)

The repr function is used for interactive echo of expressionvalues. It returns an altered version of the input string in whichcontrol codes, some BMP codepoints, and all non-BMP codepoints arereplaced with escape codes. As demonstrated above, it allows one toidentify the characters in a string, regardless of how they are displayed.

Normal and error output are generally kept separate (on separate lines)from code input and each other. They each get different highlight colors.

For SyntaxError tracebacks, the normal ‘^’ marking where the error wasdetected is replaced by coloring the text with an error highlight.When code run from a file causes other exceptions, one may right clickon a traceback line to jump to the corresponding line in an IDLE editor.The file will be opened if necessary.

Shell has a special facility for squeezing output lines down to a‘Squeezed text’ label. This is done automaticallyfor output over N lines (N = 50 by default).N can be changed in the PyShell section of the Generalpage of the Settings dialog. Output with fewer lines can be squeezed byright clicking on the output. This can be useful lines long enough to slowdown scrolling.

Squeezed output is expanded in place by double-clicking the label.It can also be sent to the clipboard or a separate view window byright-clicking the label.

Developing tkinter applications¶

IDLE is intentionally different from standard Python in order tofacilitate development of tkinter programs. Enter importtkinterastk;root=tk.Tk() in standard Python and nothing appears. Enter the samein IDLE and a tk window appears. In standard Python, one must also enterroot.update() to see the window. IDLE does the equivalent in thebackground, about 20 times a second, which is about every 50 milliseconds.Next enter b=tk.Button(root,text='button');b.pack(). Again,nothing visibly changes in standard Python until one enters root.update().

Most tkinter programs run root.mainloop(), which usually does notreturn until the tk app is destroyed. If the program is run withpython-i or from an IDLE editor, a >>> shell prompt does notappear until mainloop() returns, at which time there is nothing leftto interact with.

When running a tkinter program from an IDLE editor, one can comment outthe mainloop call. One then gets a shell prompt immediately and caninteract with the live application. One just has to remember tore-enable the mainloop call when running in standard Python.

Running without a subprocess¶

By default, IDLE executes user code in a separate subprocess via a socket,which uses the internal loopback interface. This connection is notexternally visible and no data is sent to or received from the Internet.If firewall software complains anyway, you can ignore it.

If the attempt to make the socket connection fails, Idle will notify you.Such failures are sometimes transient, but if persistent, the problemmay be either a firewall blocking the connection or misconfiguration ofa particular system. Until the problem is fixed, one can run Idle withthe -n command line switch.

If IDLE is started with the -n command line switch it will run in asingle process and will not create the subprocess which runs the RPCPython execution server. This can be useful if Python cannot createthe subprocess or the RPC socket interface on your platform. However,in this mode user code is not isolated from IDLE itself. Also, theenvironment is not restarted when Run/Run Module (F5) is selected. Ifyour code has been modified, you must reload() the affected modules andre-import any specific items (e.g. from foo import baz) if the changesare to take effect. For these reasons, it is preferable to run IDLEwith the default subprocess if at all possible.

Help and preferences¶

Help sources¶

Help menu entry “IDLE Help” displays a formatted html version of theIDLE chapter of the Library Reference. The result, in a read-onlytkinter text window, is close to what one sees in a web browser.Navigate through the text with a mousewheel,the scrollbar, or up and down arrow keys held down.Or click the TOC (Table of Contents) button and select a sectionheader in the opened box.

Help menu entry “Python Docs” opens the extensive sources of help,including tutorials, available at, where ‘x.y’is the currently running Python version. If your systemhas an off-line copy of the docs (this may be an installation option),that will be opened instead.

Selected URLs can be added or removed from the help menu at any time using theGeneral tab of the Configure IDLE dialog.

Setting preferences¶

The font preferences, highlighting, keys, and general preferences can bechanged via Configure IDLE on the Option menu.Non-default user settings are saved in a .idlerc directory in the user’shome directory. Problems caused by bad user configuration files are solvedby editing or deleting one or more of the files in .idlerc.

On the Font tab, see the text sample for the effect of font face and sizeon multiple characters in multiple languages. Edit the sample to addother characters of personal interest. Use the sample to selectmonospaced fonts. If particular characters have problems in Shell or aneditor, add them to the top of the sample and try changing first sizeand then font.

On the Highlights and Keys tab, select a built-in or custom color themeand key set. To use a newer built-in color theme or key set with olderIDLEs, save it as a new custom theme or key set and it well be accessibleto older IDLEs.

IDLE on macOS¶

Under System Preferences: Dock, one can set “Prefer tabs when openingdocuments” to “Always”. This setting is not compatible with the tk/tkinterGUI framework used by IDLE, and it breaks a few IDLE features.


IDLE contains an extension facility. Preferences for extensions can bechanged with the Extensions tab of the preferences dialog. See thebeginning of config-extensions.def in the idlelib directory for furtherinformation. The only current default extension is zzdummy, an examplealso used for testing.