Next / Previous / Contents

22. The Scrollbar widget

A number of widgets, such as listboxes and canvases, can act like sliding windows into a larger virtual area. You can connect scrollbar widgets to them to give the user a way to slide the view around relative to the contents. Here's a screen shot of an entry widget with an associated scrollbar widget:

  • Scrollbars can be horizontal, like the one shown above, or vertical. A widget that has two scrollable dimensions, such as a canvas or listbox, can have both a horizontal and a vertical scrollbar.

  • The slider, or scroll thumb, is the raised-looking rectangle that shows the current scroll position.

  • The two triangular arrowheads at each end are used for moving the position by small steps. The one on the left or top is called arrow1, and the one on the right or bottom is called arrow2.

  • The trough is the sunken-looking area visible behind the arrowheads and slider. The trough is divided into two areas named trough1 (above or to the left of the slider) and trough2 (below or to the right of the slider).

  • The slider's size and position, relative to the length of the entire widget, show the size and position of the view relative to its total size. For example, if a vertical scrollbar is associated with a listbox, and its slider extends from 50% to 75% of the height of the scrollbar, that means that the visible part of the listbox shows that portion of the overall list starting at the halfway mark and ending at the three-quarter mark.

  • In a horizontal scrollbar, clicking B1 (button 1) on the left arrowhead moves the view by a small amount to the left. Clicking B1 on the right arrowhead moves the view by that amount to the right. For a vertical scrollbar, clicking the upward- and downward-pointing arrowheads moves the view small amounts up or down. Refer to the discussion of the associated widget to find out the exact amount that these actions move the view.

  • The user can drag the slider with B1 or B2 (the middle button) to move the view.

  • For a horizontal scrollbar, clicking B1 in the trough to the left of the slider moves the view left by a page, and clicking B1 in the trough to the right of the slider moves the view a page to the right. For a vertical scrollbar, the corresponding actions move the view a page up or down.

  • Clicking B2 anywhere along the trough moves the slider so that its left or top end is at the mouse, or as close to it as possible.

The normalized position of the scrollbar refers to a number in the closed interval [0.0, 1.0] that defines the slider's position. For vertical scrollbars, position 0.0 is at the top and 1.0 at the bottom; for horizontal scrollbars, position 0.0 is at the left end and 1.0 at the right.

To create a new Scrollbar widget as the child of a root window or frame parent:

    w = tk.Scrollbar(parent, option, ...)

The constructor returns the new Scrollbar widget. Options for scrollbars include:

Table 31. Scrollbar widget options

activebackground The color of the slider and arrowheads when the mouse is over them. See Section 5.3, “Colors”.
activerelief By default, the slider is shown with the tk.RAISED relief style. To display the slider with a different relief style when the mouse is over the slider.
bg or background The color of the slider and arrowheads when the mouse is not over them.
bd or borderwidth The width of the 3-d borders around the entire perimeter of the trough, and also the width of the 3-d effects on the arrowheads and slider. Default is no border around the trough, and a two-pixel border around the arrowheads and slider. For possible values, see Section 5.1, “Dimensions”.
command A procedure to be called whenever the scrollbar is moved. For a discussion of the calling sequence, see Section 22.1, “The Scrollbar command callback”.
cursor The cursor that appears when the mouse is over the scrollbar. See Section 5.8, “Cursors”.
elementborderwidth The width of the borders around the arrowheads and slider. The default is elementborderwidth=-1, which means to use the value of the borderwidth option.
highlightbackground The color of the focus highlight when the scrollbar does not have focus. See Section 53, “Focus: routing keyboard input”.
highlightcolor The color of the focus highlight when the scrollbar has the focus.
highlightthickness The thickness of the focus highlight. Default is 1. Set to 0 to suppress display of the focus highlight.
jump This option controls what happens when a user drags the slider. Normally (jump=0), every small drag of the slider causes the command callback to be called. If you set this option to 1, the callback isn't called until the user releases the mouse button.
orient Set orient=tk.HORIZONTAL for a horizontal scrollbar, orient=tk.VERTICAL for a vertical one (the default orientation).
relief Controls the relief style of the widget; the default style is tk.SUNKEN. This option has no effect in Windows.
repeatdelay This option controls how long button 1 has to be held down in the trough before the slider starts moving in that direction repeatedly. Default is repeatdelay=300, and the units are milliseconds.
repeatinterval This option controls how often slider movement will repeat when button 1 is held down in the trough. Default is repeatinterval=100, and the units are milliseconds.
takefocus Normally, you can tab the focus through a scrollbar widget; see Section 53, “Focus: routing keyboard input”. Set takefocus=0 if you don't want this behavior. The default key bindings for scrollbars allow the user to use the ← and → arrow keys to move horizontal scrollbars, and they can use the ↑ and ↓ keys to move vertical scrollbars.
troughcolor The color of the trough.
width Width of the scrollbar (its y dimension if horizontal, and its x dimension if vertical). Default is 16. For possible values, see Section 5.1, “Dimensions”.

Methods on scrollbar objects include:


If no argument is provided, this method returns one of the strings 'arrow1', 'arrow2', 'slider', or '', depending on where the mouse is. For example, the method returns 'slider' if the mouse is on the slider. The empty string is returned if the mouse is not currently on any of these three controls.

To highlight one of the controls (using its activerelief relief style and its activebackground color), call this method and pass a string identifying the control you want to highlight, one of 'arrow1', 'arrow2', or 'slider'.

.delta(dx, dy)

Given a mouse movement of (dx, dy) in pixels, this method returns the float value that should be added to the current slider position to achieve that same movement. The value must be in the closed interval [-1.0, 1.0].

.fraction(x, y)

Given a pixel location (x, y), this method returns the corresponding normalized slider position in the interval [0.0, 1.0] that is closest to that location.


Returns two numbers (a, b) describing the current position of the slider. The a value gives the position of the left or top edge of the slider, for horizontal and vertical scrollbars respectively; the b value gives the position of the right or bottom edge. Each value is in the interval [0.0, 1.0] where 0.0 is the leftmost or top position and 1.0 is the rightmost or bottom position. For example, if the slider extends from halfway to three-quarters of the way along the trough, you might get back the tuple (0.5,0.75).

.identify(x, y)

This method returns a string indicating which (if any) of the components of the scrollbar are under the given (x, y) coordinates. The return value is one of 'arrow1', 'trough1', 'slider', 'trough2', 'arrow2', or the empty string '' if that location is not on any of the scrollbar components.

.set(first, last)

To connect a scrollbar to another widget w, set w's xscrollcommand or yscrollcommand to the scrollbar's .set method. The arguments have the same meaning as the values returned by the .get() method. Please note that moving the scrollbar's slider does not move the corresponding widget.