IDLE
****

**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 colorizing of
  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
  search through multiple files (grep)

* debugger with persistent breakpoints, stepping, and viewing of
  global and local namespaces

* configuration, browsers, and other dialogs


Menus
=====

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

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

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


File menu (Shell and Editor)
----------------------------

New File
   Create a new file editing window.

Open…
   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
   a tree structure.  In the shell, open a module first.

Path Browser
   Show sys.path directories, modules, functions, classes and methods
   in a tree structure.

Save
   Save the current window to the associated file, if there is one.
   Windows that have been changed since being opened or last saved
   have a * before and 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 the new associated file for the window.

Save Copy As…
   Save the current window to different file without changing the
   associated file.

Print Window
   Print the current window to the default printer.

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

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


Edit menu (Shell and Editor)
----------------------------

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

Redo
   Redo the last undone change to the current window.

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

Copy
   Copy selection into the system-wide clipboard.

Paste
   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.

Find…
   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.

Replace…
   Open a search-and-replace dialog.

Go to Line
   Move cursor to the line number requested and make that line
   visible.

Show Completions
   Open a scrollable list allowing selection of keywords and
   attributes. See Completions 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
   with function parameter hints.  See Calltips in the Editing 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
   using 4 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
   Python community is 4 spaces.

Format Paragraph
   Reformat the current blank-line-delimited paragraph in comment
   block or multiline string or selected line in a string.  All lines
   in the paragraph 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
   last non-whitespace character of a line by applying str.rstrip to
   each line, including lines within multiline strings.


Run menu (Editor window only)
-----------------------------

Run Module
   Do Check Module.  If no error, restart the shell to clean the
   environment, then execute the module.  Output is displayed in the
   Shell window.  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 -i
   file" at a command line.

Run… Customized
   Same as Run Module, but run the module with customized settings.
   *Command Line Arguments* extend "sys.argv" as if passed on 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 the module has not been saved IDLE will either prompt the user
   to save or autosave, as selected in the General tab of the Idle
   Settings dialog.  If there is a syntax error, the approximate
   location is indicated in the Editor 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.

Previous History
   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
   filename and line number.  If found, open the file if not already
   open, and show the line.  Use this to view source lines referenced
   in an exception traceback and lines found by Find in Files. Also
   available in the context menu of the Shell window and Output
   windows.

Debugger (toggle)
   When activated, code entered in the Shell or run from an Editor
   will run under the debugger.  In the Editor, breakpoints can be set
   with the context menu.  This feature is still incomplete and
   somewhat experimental.

Stack Viewer
   Show the stack traceback of the last exception in a tree widget,
   with access 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 and size, additional help sources, and extensions.
   On macOS, open the configuration dialog by selecting Preferences in
   the application menu. For more details, see Setting 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
   context of the code which has scrolled above the top of the window.
   See Code Context in the Editing and Navigation section below.

Show/Hide Line Numbers (Editor Window only)
   Open a column to the left of the edit window which shows the number
   of each line of text.  The default is off, which may be changed in
   the preferences (see Setting preferences).

Zoom/Restore Height
   Toggles the window between normal size and maximum height. The
   initial size defaults to 40 lines by 80 chars unless changed on the
   General tab of the Configure IDLE dialog.  The maximum height for a
   screen is determined by momentarily maximizing a window the first
   time one is zoomed on the screen. Changing screen settings may
   invalidate the saved height.  This toggle has no 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.

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

Python Docs
   Access local Python documentation, if installed, or start a web
   browser and open docs.python.org 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 under the General tab. See the Help sources subsection below
for 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.

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

Copy
   Copy selection into the system-wide clipboard.

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

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

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 *Python Shell window* subsection below.

Squeeze
   If the cursor is over an output line, squeeze all the output
   between the 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 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.


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.


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.


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.

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.

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 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.
