IDLE is Python’s Integrated Development and Learning Environment.
Editing and navigation
Editor windows
IDLE may open editor windows when it starts, depending on settings
and how you start IDLE. Thereafter, use the File menu. There can be only
one open editor window for a given file.
The title bar contains the name of the file, the full path, and the version
of Python and IDLE running the window. The status bar contains the line
number (‘Ln’) and column number (‘Col’). Line numbers start with 1;
column numbers with 0.
IDLE assumes that files with a known .py* extension contain Python code
and 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 and
the 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 can
also use the cursor key for this)
- C-f go forward one character without deleting (usually you can
also use the cursor key for this)
- C-p go up one line (usually you can also use the cursor key for
this)
- 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 the
Python Shell window by one tab). After certain keywords (break, return etc.)
the next line is dedented. In leading indentation, Backspace deletes up
to 4 spaces if they are there. Tab inserts spaces (in the Python
Shell window one tab), number depends on Indent width. Currently, tabs
are restricted to four spaces due to Tcl/Tk limitations.
See also the indent/dedent region commands in the edit menu.
Completions
Completions are supplied for functions, classes, and attributes of classes,
both built-in and user-defined. Completions are also provided for
filenames.
The AutoCompleteWindow (ACW) will open after a predefined delay (default is
two seconds) after a ‘.’ or (in a string) an os.sep is typed. If after one
of those characters (plus zero or more other characters) a tab is typed
the ACW will open immediately if a possible continuation is found.
If there is only one possible completion for the characters entered, a
Tab will supply that completion without opening the ACW.
‘Show Completions’ will force open a completions window, by default the
C-space will open a completions window. In an empty
string, this will contain the files in the current directory. On a
blank line, it will contain the built-in and user-defined functions and
classes in the current namespaces, plus any modules imported. If some
characters have been entered, the ACW will attempt to be more specific.
If a string of characters is typed, the ACW selection will jump to the
entry most closely matching those characters. Entering a tab will
cause the longest non-ambiguous match to be entered in the Editor window or
Shell. Two tab in a row will supply the current ACW selection, as
will return or a double click. Cursor keys, Page Up/Down, mouse selection,
and the scroll wheel all operate on the ACW.
“Hidden” attributes can be accessed by typing the beginning of hidden
name after a ‘.’, e.g. ‘_’. This allows access to modules with
__all__ set, or to class-private attributes.
Completions and the ‘Expand Word’ facility can save a lot of typing!
Completions are currently limited to those in the namespaces. Names in
an Editor window which are not via __main__ and sys.modules will
not be found. Run the module once with your imports to correct this situation.
Note that IDLE itself places quite a few modules in sys.modules, so
much can be found by default, e.g. the re module.
If you don’t like the ACW popping up unbidden, simply make the delay
longer or disable the extension.
Calltips
A calltip is shown when one types ( after the name of an accessible
function. A name expression may include dots and subscripts. A calltip
remains until it is clicked, the cursor is moved out of the argument area,
or ) is typed. When the cursor is in the argument part of a definition,
the menu or shortcut display a calltip.
A calltip consists of the function signature and the first line of the
docstring. For builtins without an accessible signature, the calltip
consists of all lines up the fifth line or the first blank line. These
details may change.
The set of accessible functions depends on what modules have been imported
into the user process, including those imported by Idle itself,
and what definitions have been run, all since the last restart.
For example, restart the Shell and enter itertools.count(. A calltip
appears because Idle imports itertools into the user process for its own use.
(This could change.) Enter turtle.write( and nothing appears. Idle does
not import turtle. The menu or shortcut do nothing either. Enter
import turtle and then turtle.write( will work.
In an editor, import statements have no effect until one runs the file. One
might want to run a file after writing the import statements at the top,
or immediately run an existing file before editing.
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 executed
until one hits Return. One may edit pasted code first.
If one pastes more that one statement into Shell, the result will be a
SyntaxError when multiple statements are compiled as if they were one.
The editing features described in previous subsections work when entering
code 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. On
macOS 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, and
user error. For Python code, at the shell prompt or in an editor, these are
keywords, builtin class and function names, names following class and
def, strings, and comments. For any text window, these are the cursor (when
present), found text (when possible), and selected text.
Text coloring is done in the background, so uncolorized text is occasionally
visible. To change the color scheme, use the Configure IDLE dialog
Highlighting tab. The marking of debugger breakpoint lines in the editor and
text in popups and dialogs is not user-configurable.
Startup and code execution
Upon startup with the -s option, IDLE will execute the file referenced by
the environment variables IDLESTARTUP or PYTHONSTARTUP.
IDLE first checks for IDLESTARTUP; if IDLESTARTUP is present the file
referenced is run. If IDLESTARTUP is not present, IDLE checks for
PYTHONSTARTUP. Files referenced by these environment variables are
convenient places to store functions that are used frequently from the IDLE
shell, or for executing import statements to import common modules.
In addition, Tk also loads a startup file if it is present. Note that the
Tk file is loaded unconditionally. This additional file is .Idle.py and is
looked for in the user’s home directory. Statements in this file will be
executed in the Tk namespace, so this file is not useful for importing
functions to be used from IDLE’s Python shell.
Command line usage
idle.py [-c command] [-d] [-e] [-h] [-i] [-r file] [-s] [-t title] [-] [arg] ...
-c command run command in the shell window
-d enable debugger and open shell window
-e open editor window
-h print help message with legal combinations and exit
-i open shell window
-r file run file in shell window
-s run $IDLESTARTUP or $PYTHONSTARTUP first, in shell window
-t title set title of shell window
- run stdin in shell (- must be last option before args)
If there are arguments:
- If
-, -c, or r is used, all arguments are placed in
sys.argv[1:...] and sys.argv[0] is set to '', '-c',
or '-r'. No editor window is opened, even if that is the default
set in the Options dialog.
- Otherwise, arguments are files opened for editing and
sys.argv reflects the arguments passed to IDLE itself.
Startup failure
IDLE uses a socket to communicate between the IDLE GUI process and the user
code execution process. A connection must be established whenever the Shell
starts or restarts. (The latter is indicated by a divider line that says
‘RESTART’). If the user process fails to connect to the GUI process, it
displays a Tk error box with a ‘cannot connect’ message that directs the
user here. It then exits.
A common cause of failure is a user-written file with the same name as a
standard library module, such as random.py and tkinter.py. When such a
file 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 the
user file.
Though less common than in the past, an antivirus or firewall program may
stop the connection. If the program cannot be taught to allow the
connection, then it must be turned off for IDLE to work. It is safe to
allow this internal connection because no data is visible on external
ports. A similar problem is a network mis-configuration that blocks
connections.
Python installation issues occasionally stop IDLE: multiple versions can
clash, or a single installation might need admin access. If one undo the
clash, or cannot or does not want to run as admin, it might be easiest to
completely remove Python and start over.
A zombie pythonw.exe process could be a problem. On Windows, use Task
Manager to detect and stop one. Sometimes a restart initiated by a program
crash or Keyboard Interrupt (control-C) may fail to connect. Dismissing
the error box or Restart Shell on the Shell menu 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 error
message should be displayed. Leaving aside random disk glitches, this can
be prevented by never editing the files by hand, using the configuration
dialog, under Options, instead Options. Once it happens, the solution may
be to delete one or more of the configuration files.
If IDLE quits with no message, and it was not started from a console, try
starting from a console (python -m idlelib) and see if a message appears.
Running user code
With rare exceptions, the result of executing Python code with IDLE is
intended 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 affect
visible results. For instance, sys.modules starts with more entries,
and threading.activeCount() returns 2 instead of 1.
By default, IDLE runs user code in a separate OS process rather than in
the user interface process that runs the shell and editor. In the execution
process, it replaces sys.stdin, sys.stdout, and sys.stderr
with objects that get input from and send output to the Shell window.
The original values stored in sys.__stdin__, sys.__stdout__, and
sys.__stderr__ are not touched, but may be None.
When Shell has the focus, it controls the keyboard and screen. This is
normally transparent, but functions that directly access the keyboard
and screen will not work. These include system-specific functions that
determine whether a key has been pressed and if so, which.
IDLE’s standard stream replacements are not inherited by subprocesses
created in the execution process, whether directly by user code or by modules
such as multiprocessing. If such subprocess use input from sys.stdin
or print or write to sys.stdout or sys.stderr,
IDLE should be started in a command line window. The secondary subprocess
will 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 screen
will not work correctly.
User output in Shell
When a program outputs text, the result is determined by the
corresponding output device. When IDLE executes user code, sys.stdout
and sys.stderr are connected to the display area of IDLE’s Shell. Some of
its features are inherited from the underlying Tk Text widget. Others
are programmed additions. Where it matters, Shell is designed for development
rather than production runs.
For instance, Shell never throws away output. A program that sends unlimited
output 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.
Text widgets display a subset of Unicode, the Basic Multilingual Plane (BMP).
Which characters get a proper glyph instead of a replacement box depends on
the operating system and installed fonts. Newline characters cause following
text to appear on a new line, but other control characters are either
replaced with a box or deleted. However, repr(), which is used for
interactive echo of expression values, replaces control characters,
some BMP codepoints, and all non-BMP characters with escape codes
before they are output.
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 was
detected is replaced by coloring the text with an error highlight.
When code run from a file causes other exceptions, one may right click
on 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 automatically
for output over N lines (N = 50 by default).
N can be changed in the PyShell section of the General
page of the Settings dialog. Output with fewer lines can be squeezed by
right clicking on the output. This can be useful lines long enough to slow
down 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 by
right-clicking the label.
Developing tkinter applications
IDLE is intentionally different from standard Python in order to
facilitate development of tkinter programs. Enter import tkinter as tk;
root = tk.Tk() in standard Python and nothing appears. Enter the same
in IDLE and a tk window appears. In standard Python, one must also enter
root.update() to see the window. IDLE does the equivalent in the
background, about 20 times a second, which is about every 50 milleseconds.
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 not
return until the tk app is destroyed. If the program is run with
python -i or from an IDLE editor, a >>> shell prompt does not
appear until mainloop() returns, at which time there is nothing left
to interact with.
When running a tkinter program from an IDLE editor, one can comment out
the mainloop call. One then gets a shell prompt immediately and can
interact with the live application. One just has to remember to
re-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 not
externally 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 problem
may be either a firewall blocking the connection or misconfiguration of
a particular system. Until the problem is fixed, one can run Idle with
the -n command line switch.
If IDLE is started with the -n command line switch it will run in a
single process and will not create the subprocess which runs the RPC
Python execution server. This can be useful if Python cannot create
the subprocess or the RPC socket interface on your platform. However,
in this mode user code is not isolated from IDLE itself. Also, the
environment is not restarted when Run/Run Module (F5) is selected. If
your code has been modified, you must reload() the affected modules and
re-import any specific items (e.g. from foo import baz) if the changes
are to take effect. For these reasons, it is preferable to run IDLE
with the default subprocess if at all possible.
Deprecated since version 3.4.
Help and preferences
Help sources
Help menu entry “IDLE Help” displays a formatted html version of the
IDLE chapter of the Library Reference. The result, in a read-only
tkinter 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 section
header in the opened box.
Help menu entry “Python Docs” opens the extensive sources of help,
including tutorials, available at docs.python.org/x.y, where ‘x.y’
is the currently running Python version. If your system
has 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 the
General tab of the Configure IDLE dialog .
Setting preferences
The font preferences, highlighting, keys, and general preferences can be
changed via Configure IDLE on the Option menu. Keys can be user defined;
IDLE ships with four built-in key sets. In addition, a user can create a
custom key set in the Configure IDLE dialog under the keys tab.
IDLE on macOS
Under System Preferences: Dock, one can set “Prefer tabs when opening
documents” to “Always”. This setting is not compatible with the tk/tkinter
GUI framework used by IDLE, and it breaks a few IDLE features.
Extensions
IDLE contains an extension facility. Preferences for extensions can be
changed with the Extensions tab of the preferences dialog. See the
beginning of config-extensions.def in the idlelib directory for further
information. The only current default extension is zzdummy, an example
also used for testing.