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 on the
Format menu.
Search and Replace
Any selection becomes a search target. However, only selections within
a line work because searches are only performed within lines with the
terminal newline removed. If [x] Regular expresion
is checked, the
target is interpreted according to the Python re module.
Completions
Completions are supplied, when requested and available, for module
names, attributes of classes or functions, or filenames. Each request
method displays a completion box with existing names. (See tab
completions below for an exception.) For any box, change the name
being completed and the item highlighted in the box by
typing 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.
One way to open a box is to type a key character and wait for a
predefined interval. This defaults to 2 seconds; customize it
in the settings dialog. (To prevent auto popups, set the delay to a
large number of milliseconds, such as 100000000.) For imported module
names or class or function attributes, type ‘.’.
For filenames in the root directory, type os.sep
or
os.altsep
immediately after an opening quote. (On Windows,
one can specify a drive first.) Move into subdirectories by typing a
directory name and a separator.
Instead of waiting, or after a box is closed, open a completion box
immediately with Show Completions on the Edit menu. The default hot
key is C-space. If one types a prefix for the desired name
before opening the box, the first match or near miss is made visible.
The result is the same as if one enters a prefix
after the box is displayed. Show Completions after a quote completes
filenames in the current directory instead of a root directory.
Hitting Tab after a prefix usually has the same effect as Show
Completions. (With no prefix, it indents.) However, if there is only
one match to the prefix, that match is immediately added to the editor
text without opening a box.
Invoking ‘Show Completions’, or hitting Tab after a prefix,
outside of a string and without a preceding ‘.’ opens a box with
keywords, builtin names, and available module-level names.
When editing code in an editor (as oppose to Shell), increase the
available module-level names by running your code
and not restarting the Shell thereafter. This is especially useful
after adding imports at the top of a file. This also increases
possible attribute completions.
Completion boxes initially exclude names beginning with ‘_’ or, for
modules, not included in ‘__all__’. The hidden names can be accessed
by typing ‘_’ after ‘.’, either before or after the box is opened.
Calltips
A calltip is shown automatically when one types ( after the name
of an accessible function. A function 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. Whenever the
cursor is in the argument part of a definition, select Edit and “Show
Call Tip” on the menu or enter its shortcut to display a calltip.
The calltip consists of the function’s signature and docstring up to
the latter’s first blank line or the fifth non-blank line. (Some builtin
functions lack an accessible signature.) A ‘/’ or ‘*’ in the signature
indicates that the preceding or following arguments are passed by
position or name (keyword) only. Details are subject to change.
In Shell, the accessible functions depends on what modules have been
imported 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 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 itself import turtle. The menu entry and shortcut also do
nothing. Enter import turtle
. 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, after
adding function definitions, or after opening an existing file.
Code Context
Within an editor window containing Python code, code context can be toggled
in order to show or hide a pane at the top of the window. When shown, this
pane freezes the opening lines for block code, such as those beginning with
class
, def
, or if
keywords, that would have otherwise scrolled
out of view. The size of the pane will be expanded and contracted as needed
to show the all current levels of context, up to the maximum number of
lines defined in the Configure IDLE dialog (which defaults to 15). If there
are no current context lines and the feature is toggled on, a single blank
line will display. Clicking on a line in the context pane will move that
line to the top of the editor.
The text and background colors for the context pane can be configured under
the Highlights tab in the Configure IDLE dialog.
Shell window
In IDLE’s Shell, enter, edit, and recall complete statements. (Most
consoles and terminals only work with a single physical line at a time).
Submit a single-line statement for execution by hitting Return
with the cursor anywhere on the line. If a line is extended with
Backslash (\), the cursor must be on the last physical line.
Submit a multi-line compound statement by entering a blank line after
the statement.
When one pastes code into Shell, it is not compiled and possibly executed
until one hits Return, as specified above.
One may edit pasted code first.
If one pastes more than one statement into Shell, the result will be a
SyntaxError
when multiple statements are compiled as if they were one.
Lines containing RESTART
mean that the user execution process has been
re-started. This occurs when the user execution process has crashed,
when one requests a restart on the Shell menu, or when one runs code
in an editor window.
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 the cursor is 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.
IDLE also highlights the soft keywords match
,
case
, and _
in
pattern-matching statements. However, this highlighting is not perfect and
will be incorrect in some rare cases, including some _
-s in case
patterns.
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
usually displays a Tk
error box with a ‘cannot connect’ message
that directs the user here. It then exits.
One specific connection failure on Unix systems results from
misconfigured masquerading rules somewhere in a system’s network setup.
When IDLE is started from a terminal, one will see a message starting
with ** Invalid host:
.
The valid value is 127.0.0.1 (idlelib.rpc.LOCALHOST)
.
One can diagnose with tcpconnect -irv 127.0.0.1 6543
in one
terminal window and tcplisten <same args>
in another.
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 check for one and stop it if there is. Sometimes a restart
initiated by a program crash or Keyboard Interrupt (control-C) may fail
to connect. Dismissing the error box or using 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. Instead, use the
configuration dialog, under Options. Once there is an error in a user
configuration file, the best solution may be to delete it and start over
with the settings dialog.
If IDLE quits with no message, and it was not started from a console, try
starting it from a console or terminal (python -m idlelib
) and see if
this results in an error message.
On Unix-based systems with tcl/tk older than 8.6.11
(see
About IDLE
) certain characters of certain fonts can cause
a tk failure with a message to the terminal. This can happen either
if one starts IDLE to edit a file with such a character or later
when 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 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.active_count()
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
.
Sending print output from one process to a text widget in another is
slower than printing to a system terminal in the same process.
This has the most effect when printing multiple arguments, as the string
for each argument, each separator, the newline are sent separately.
For development, this is usually not a problem, but if one wants to
print faster in IDLE, format and join together everything one wants
displayed together and then print a single string. Both format strings
and str.join()
can help combine fields and lines.
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. (On Windows,
use python
or py
rather than pythonw
or pyw
.)
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.
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.
The IDLE code running in the execution process adds frames to the call stack
that would not be there otherwise. IDLE wraps sys.getrecursionlimit
and
sys.setrecursionlimit
to reduce the effect of the additional stack
frames.
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 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.
A Tk Text widget, and hence IDLE’s Shell, displays characters (codepoints) in
the BMP (Basic Multilingual Plane) subset of Unicode. Which characters are
displayed with a proper glyph and which with a replacement box depends on the
operating system and installed fonts. Tab characters cause the following text
to begin after the next tab stop. (They occur every 8 ‘characters’). Newline
characters cause following text to appear on a new line. Other control
characters are ignored or displayed as a space, box, or something else,
depending on the operating system and font. (Moving the text cursor through
such output with arrow keys may exhibit some surprising spacing behavior.)
>>> s = 'a\tb\a<\x02><\r>\bc\nd' # Enter 22 chars.
>>> len(s)
14
>>> s # Display repr(s)
'a\tb\x07<\x02><\r>\x08c\nd'
>>> print(s, end='') # Display s as is.
# Result varies by OS and font. Try it.
The repr
function is used for interactive echo of expression
values. It returns an altered version of the input string in which
control codes, some BMP codepoints, and all non-BMP codepoints are
replaced with escape codes. As demonstrated above, it allows one to
identify 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 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 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 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.
Non-default user settings are saved in a .idlerc
directory in the user’s
home directory. Problems caused by bad user configuration files are solved
by 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 size
on multiple characters in multiple languages. Edit the sample to add
other characters of personal interest. Use the sample to select
monospaced fonts. If particular characters have problems in Shell or an
editor, add them to the top of the sample and try changing first size
and then font.
On the Highlights and Keys tab, select a built-in or custom color theme
and key set. To use a newer built-in color theme or key set with older
IDLEs, save it as a new custom theme or key set and it well be accessible
to older IDLEs.
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.