24.1. Tkinter — Python interface to Tcl/Tk
The Tkinter module (“Tk interface”) is the standard Python interface to
the Tk GUI toolkit. Both Tk and Tkinter are available on most Unix
platforms, as well as on Windows systems. (Tk itself is not part of Python; it
is maintained at ActiveState.)
Note
Tkinter has been renamed to tkinter in Python 3.0. The
2to3 tool will automatically adapt imports when converting your
sources to 3.0.
24.1.1. Tkinter Modules
Most of the time, the Tkinter module is all you really need, but a number
of additional modules are available as well. The Tk interface is located in a
binary module named _tkinter. This module contains the low-level
interface to Tk, and should never be used directly by application programmers.
It is usually a shared library (or DLL), but might in some cases be statically
linked with the Python interpreter.
In addition to the Tk interface module, Tkinter includes a number of
Python modules. The two most important modules are the Tkinter module
itself, and a module called Tkconstants. The former automatically imports
the latter, so to use Tkinter, all you need to do is to import one module:
Or, more often:
-
class
Tkinter.Tk(screenName=None, baseName=None, className='Tk', useTk=1)
The Tk class is instantiated without arguments. This creates a toplevel
widget of Tk which usually is the main window of an application. Each instance
has its own associated Tcl interpreter.
Changed in version 2.4:
Changed in version 2.4: The useTk parameter was added.
-
Tkinter.Tcl(screenName=None, baseName=None, className='Tk', useTk=0)
The Tcl() function is a factory function which creates an object much like
that created by the Tk class, except that it does not initialize the Tk
subsystem. This is most often useful when driving the Tcl interpreter in an
environment where one doesn’t want to create extraneous toplevel windows, or
where one cannot (such as Unix/Linux systems without an X server). An object
created by the Tcl() object can have a Toplevel window created (and the Tk
subsystem initialized) by calling its loadtk() method.
New in version 2.4:
New in version 2.4.
Other modules that provide Tk support include:
ScrolledText- Text widget with a vertical scroll bar built in.
tkColorChooser- Dialog to let the user choose a color.
tkCommonDialog- Base class for the dialogs defined in the other modules listed here.
tkFileDialog- Common dialogs to allow the user to specify a file to open or save.
tkFont- Utilities to help work with fonts.
tkMessageBox- Access to standard Tk dialog boxes.
tkSimpleDialog- Basic dialogs and convenience functions.
Tkdnd- Drag-and-drop support for
Tkinter. This is experimental and should become
deprecated when it is replaced with the Tk DND.
turtle- Turtle graphics in a Tk window.
These have been renamed as well in Python 3.0; they were all made submodules of
the new tkinter package.
24.1.3. A (Very) Quick Look at Tcl/Tk
The class hierarchy looks complicated, but in actual practice, application
programmers almost always refer to the classes at the very bottom of the
hierarchy.
Notes:
- These classes are provided for the purposes of organizing certain functions
under one namespace. They aren’t meant to be instantiated independently.
- The
Tk class is meant to be instantiated only once in an application.
Application programmers need not instantiate one explicitly, the system creates
one whenever any of the other classes are instantiated.
- The
Widget class is not meant to be instantiated, it is meant only
for subclassing to make “real” widgets (in C++, this is called an ‘abstract
class’).
To make use of this reference material, there will be times when you will need
to know how to read short passages of Tk and how to identify the various parts
of a Tk command. (See section Mapping Basic Tk into Tkinter for the
Tkinter equivalents of what’s below.)
Tk scripts are Tcl programs. Like all Tcl programs, Tk scripts are just lists
of tokens separated by spaces. A Tk widget is just its class, the options
that help configure it, and the actions that make it do useful things.
To make a widget in Tk, the command is always of the form:
classCommand newPathname options
- classCommand
- denotes which kind of widget to make (a button, a label, a menu...)
- newPathname
- is the new name for this widget. All names in Tk must be unique. To help
enforce this, widgets in Tk are named with pathnames, just like files in a
file system. The top level widget, the root, is called
. (period) and
children are delimited by more periods. For example,
.myApp.controlPanel.okButton might be the name of a widget.
- options
- configure the widget’s appearance and in some cases, its behavior. The options
come in the form of a list of flags and values. Flags are preceded by a ‘-‘,
like Unix shell command flags, and values are put in quotes if they are more
than one word.
For example:
button .fred -fg red -text "hi there"
^ ^ \_____________________/
| | |
class new options
command widget (-opt val -opt val ...)
Once created, the pathname to the widget becomes a new command. This new
widget command is the programmer’s handle for getting the new widget to
perform some action. In C, you’d express this as someAction(fred,
someOptions), in C++, you would express this as fred.someAction(someOptions),
and in Tk, you say:
.fred someAction someOptions
Note that the object name, .fred, starts with a dot.
As you’d expect, the legal values for someAction will depend on the widget’s
class: .fred disable works if fred is a button (fred gets greyed out), but
does not work if fred is a label (disabling of labels is not supported in Tk).
The legal values of someOptions is action dependent. Some actions, like
disable, require no arguments, others, like a text-entry box’s delete
command, would need arguments to specify what range of text to delete.
24.1.4. Mapping Basic Tk into Tkinter
Class commands in Tk correspond to class constructors in Tkinter.
button .fred =====> fred = Button()
The master of an object is implicit in the new name given to it at creation
time. In Tkinter, masters are specified explicitly.
button .panel.fred =====> fred = Button(panel)
The configuration options in Tk are given in lists of hyphened tags followed by
values. In Tkinter, options are specified as keyword-arguments in the instance
constructor, and keyword-args for configure calls or as instance indices, in
dictionary style, for established instances. See section
Setting Options on setting options.
button .fred -fg red =====> fred = Button(panel, fg = "red")
.fred configure -fg red =====> fred["fg"] = red
OR ==> fred.config(fg = "red")
In Tk, to perform an action on a widget, use the widget name as a command, and
follow it with an action name, possibly with arguments (options). In Tkinter,
you call methods on the class instance to invoke actions on the widget. The
actions (methods) that a given widget can perform are listed in the Tkinter.py
module.
.fred invoke =====> fred.invoke()
To give a widget to the packer (geometry manager), you call pack with optional
arguments. In Tkinter, the Pack class holds all this functionality, and the
various forms of the pack command are implemented as methods. All widgets in
Tkinter are subclassed from the Packer, and so inherit all the packing
methods. See the Tix module documentation for additional information on
the Form geometry manager.
pack .fred -side left =====> fred.pack(side = "left")
24.1.6. Handy Reference
24.1.6.1. Setting Options
Options control things like the color and border width of a widget. Options can
be set in three ways:
- At object creation time, using keyword arguments
fred = Button(self, fg = "red", bg = "blue")
- After object creation, treating the option name like a dictionary index
fred["fg"] = "red"
fred["bg"] = "blue"
- Use the config() method to update multiple attrs subsequent to object creation
fred.config(fg = "red", bg = "blue")
For a complete explanation of a given option and its behavior, see the Tk man
pages for the widget in question.
Note that the man pages list “STANDARD OPTIONS” and “WIDGET SPECIFIC OPTIONS”
for each widget. The former is a list of options that are common to many
widgets, the latter are the options that are idiosyncratic to that particular
widget. The Standard Options are documented on the options(3) man
page.
No distinction between standard and widget-specific options is made in this
document. Some options don’t apply to some kinds of widgets. Whether a given
widget responds to a particular option depends on the class of the widget;
buttons have a command option, labels do not.
The options supported by a given widget are listed in that widget’s man page, or
can be queried at runtime by calling the config() method without
arguments, or by calling the keys() method on that widget. The return
value of these calls is a dictionary whose key is the name of the option as a
string (for example, 'relief') and whose values are 5-tuples.
Some options, like bg are synonyms for common options with long names
(bg is shorthand for “background”). Passing the config() method the name
of a shorthand option will return a 2-tuple, not 5-tuple. The 2-tuple passed
back will contain the name of the synonym and the “real” option (such as
('bg', 'background')).
| Index |
Meaning |
Example |
|---|
| 0 |
option name |
'relief' |
| 1 |
option name for database lookup |
'relief' |
| 2 |
option class for database
lookup |
'Relief' |
| 3 |
default value |
'raised' |
| 4 |
current value |
'groove' |
Example:
>>> print fred.config()
{'relief' : ('relief', 'relief', 'Relief', 'raised', 'groove')}
Of course, the dictionary printed will include all the options available and
their values. This is meant only as an example.
24.1.6.2. The Packer
The packer is one of Tk’s geometry-management mechanisms. Geometry managers
are used to specify the relative positioning of the positioning of widgets
within their container - their mutual master. In contrast to the more
cumbersome placer (which is used less commonly, and we do not cover here), the
packer takes qualitative relationship specification - above, to the left of,
filling, etc - and works everything out to determine the exact placement
coordinates for you.
The size of any master widget is determined by the size of the “slave widgets”
inside. The packer is used to control where slave widgets appear inside the
master into which they are packed. You can pack widgets into frames, and frames
into other frames, in order to achieve the kind of layout you desire.
Additionally, the arrangement is dynamically adjusted to accommodate incremental
changes to the configuration, once it is packed.
Note that widgets do not appear until they have had their geometry specified
with a geometry manager. It’s a common early mistake to leave out the geometry
specification, and then be surprised when the widget is created but nothing
appears. A widget will appear only after it has had, for example, the packer’s
pack() method applied to it.
The pack() method can be called with keyword-option/value pairs that control
where the widget is to appear within its container, and how it is to behave when
the main application window is resized. Here are some examples:
fred.pack() # defaults to side = "top"
fred.pack(side = "left")
fred.pack(expand = 1)
24.1.6.3. Packer Options
For more extensive information on the packer and the options that it can take,
see the man pages and page 183 of John Ousterhout’s book.
- anchor
- Anchor type. Denotes where the packer is to place each slave in its parcel.
- expand
- Boolean,
0 or 1.
- fill
- Legal values:
'x', 'y', 'both', 'none'.
- ipadx and ipady
- A distance - designating internal padding on each side of the slave widget.
- padx and pady
- A distance - designating external padding on each side of the slave widget.
- side
- Legal values are:
'left', 'right', 'top', 'bottom'.
24.1.6.5. The Window Manager
In Tk, there is a utility command, wm, for interacting with the window
manager. Options to the wm command allow you to control things like titles,
placement, icon bitmaps, and the like. In Tkinter, these commands have
been implemented as methods on the Wm class. Toplevel widgets are
subclassed from the Wm class, and so can call the Wm methods
directly.
To get at the toplevel window that contains a given widget, you can often just
refer to the widget’s master. Of course if the widget has been packed inside of
a frame, the master won’t represent a toplevel window. To get at the toplevel
window that contains an arbitrary widget, you can call the _root() method.
This method begins with an underscore to denote the fact that this function is
part of the implementation, and not an interface to Tk functionality.
Here are some examples of typical usage:
from Tkinter import *
class App(Frame):
def __init__(self, master=None):
Frame.__init__(self, master)
self.pack()
# create the application
myapp = App()
#
# here are method calls to the window manager class
#
myapp.master.title("My Do-Nothing Application")
myapp.master.maxsize(1000, 400)
# start the program
myapp.mainloop()
24.1.6.6. Tk Option Data Types
- anchor
- Legal values are points of the compass:
"n", "ne", "e", "se",
"s", "sw", "w", "nw", and also "center".
- bitmap
- There are eight built-in, named bitmaps:
'error', 'gray25',
'gray50', 'hourglass', 'info', 'questhead', 'question',
'warning'. To specify an X bitmap filename, give the full path to the file,
preceded with an @, as in "@/usr/contrib/bitmap/gumby.bit".
- boolean
- You can pass integers 0 or 1 or the strings
"yes" or "no" .
- callback
This is any Python function that takes no arguments. For example:
def print_it():
print "hi there"
fred["command"] = print_it
- color
- Colors can be given as the names of X colors in the rgb.txt file, or as strings
representing RGB values in 4 bit:
"#RGB", 8 bit: "#RRGGBB", 12 bit”
"#RRRGGGBBB", or 16 bit "#RRRRGGGGBBBB" ranges, where R,G,B here
represent any legal hex digit. See page 160 of Ousterhout’s book for details.
- cursor
- The standard X cursor names from
cursorfont.h can be used, without the
XC_ prefix. For example to get a hand cursor (XC_hand2), use the
string "hand2". You can also specify a bitmap and mask file of your own.
See page 179 of Ousterhout’s book.
- distance
- Screen distances can be specified in either pixels or absolute distances.
Pixels are given as numbers and absolute distances as strings, with the trailing
character denoting units:
c for centimetres, i for inches, m for
millimetres, p for printer’s points. For example, 3.5 inches is expressed
as "3.5i".
- font
- Tk uses a list font name format, such as
{courier 10 bold}. Font sizes with
positive numbers are measured in points; sizes with negative numbers are
measured in pixels.
- geometry
- This is a string of the form
widthxheight, where width and height are
measured in pixels for most widgets (in characters for widgets displaying text).
For example: fred["geometry"] = "200x100".
- justify
- Legal values are the strings:
"left", "center", "right", and
"fill".
- region
- This is a string with four space-delimited elements, each of which is a legal
distance (see above). For example:
"2 3 4 5" and "3i 2i 4.5i 2i" and
"3c 2c 4c 10.43c" are all legal regions.
- relief
- Determines what the border style of a widget will be. Legal values are:
"raised", "sunken", "flat", "groove", and "ridge".
- scrollcommand
- This is almost always the
set() method of some scrollbar widget, but can
be any widget method that takes a single argument. Refer to the file
Demo/tkinter/matt/canvas-with-scrollbars.py in the Python source
distribution for an example.
- wrap:
- Must be one of:
"none", "char", or "word".
24.1.6.7. Bindings and Events
The bind method from the widget command allows you to watch for certain events
and to have a callback function trigger when that event type occurs. The form
of the bind method is:
def bind(self, sequence, func, add=''):
where:
- sequence
- is a string that denotes the target kind of event. (See the bind man page and
page 201 of John Ousterhout’s book for details).
- func
- is a Python function, taking one argument, to be invoked when the event occurs.
An Event instance will be passed as the argument. (Functions deployed this way
are commonly known as callbacks.)
- add
- is optional, either
'' or '+'. Passing an empty string denotes that
this binding is to replace any other bindings that this event is associated
with. Passing a '+' means that this function is to be added to the list
of functions bound to this event type.
For example:
def turnRed(self, event):
event.widget["activeforeground"] = "red"
self.button.bind("<Enter>", self.turnRed)
Notice how the widget field of the event is being accessed in the
turnRed() callback. This field contains the widget that caught the X
event. The following table lists the other event fields you can access, and how
they are denoted in Tk, which can be useful when referring to the Tk man pages.
Tk Tkinter Event Field Tk Tkinter Event Field
-- ------------------- -- -------------------
%f focus %A char
%h height %E send_event
%k keycode %K keysym
%s state %N keysym_num
%t time %T type
%w width %W widget
%x x %X x_root
%y y %Y y_root
24.1.6.8. The index Parameter
A number of widgets require”index” parameters to be passed. These are used to
point at a specific place in a Text widget, or to particular characters in an
Entry widget, or to particular menu items in a Menu widget.
- Entry widget indexes (index, view index, etc.)
Entry widgets have options that refer to character positions in the text being
displayed. You can use these Tkinter functions to access these special
points in text widgets:
- AtEnd()
- refers to the last position in the text
- AtInsert()
- refers to the point where the text cursor is
- AtSelFirst()
- indicates the beginning point of the selected text
- AtSelLast()
- denotes the last point of the selected text and finally
- At(x[, y])
- refers to the character at pixel location x, y (with y not used in the
case of a text entry widget, which contains a single line of text).
- Text widget indexes
- The index notation for Text widgets is very rich and is best described in the Tk
man pages.
- Menu indexes (menu.invoke(), menu.entryconfig(), etc.)
Some options and methods for menus manipulate specific menu entries. Anytime a
menu index is needed for an option or a parameter, you may pass in:
- an integer which refers to the numeric position of the entry in the widget,
counted from the top, starting with 0;
- the string
'active', which refers to the menu position that is currently
under the cursor;
- the string
"last" which refers to the last menu item;
- An integer preceded by
@, as in @6, where the integer is interpreted
as a y pixel coordinate in the menu’s coordinate system;
- the string
"none", which indicates no menu entry at all, most often used
with menu.activate() to deactivate all entries, and finally,
- a text string that is pattern matched against the label of the menu entry, as
scanned from the top of the menu to the bottom. Note that this index type is
considered after all the others, which means that matches for menu items
labelled
last, active, or none may be interpreted as the above
literals, instead.
24.1.6.9. Images
Bitmap/Pixelmap images can be created through the subclasses of
Tkinter.Image:
BitmapImage can be used for X11 bitmap data.PhotoImage can be used for GIF and PPM/PGM color bitmaps.
Either type of image is created through either the file or the data
option (other options are available as well).
The image object can then be used wherever an image option is supported by
some widget (e.g. labels, buttons, menus). In these cases, Tk will not keep a
reference to the image. When the last Python reference to the image object is
deleted, the image data is deleted as well, and Tk will display an empty box
wherever the image was used.