15. tk Scale

See: https://docs.python.org/3/library/tkinter.html#tkinter.Scale
See: https://www.geeksforgeeks.org/python-scale-widget-in-tkinter/

15.1. Usage

The tkinter.Scale widget provides a slider that allows the user to select a numeric value by dragging a slider along a horizontal or vertical bar.
It is commonly used for selecting values such as volume, brightness, or percentages.
To create a scale widget, the general syntax is
(assuming import via import tkinter as tk):
scale_widget = tk.Scale(parent, option=value)
parent is the window or frame object.
Options can be passed as parameters separated by commas.
A scale can be associated with a control variable such as IntVar or DoubleVar to store its current value.

15.2. Using a scale

../_images/scale.png 
import tkinter as tk

root = tk.Tk()
root.title("Scale Example")

value = tk.IntVar(value=50)

scale = tk.Scale(
    root,
    from_=0,
    to=100,
    orient="horizontal",
    variable=value,
    length=300
)

scale.pack(padx=10, pady=10)

root.mainloop()

Tasks

  1. Modify the code so that the scale:

    • is vertical,

    • ranges from 0 to 20,

    • has a length of 100 pixels,

    • starts at 10.

    ../_images/scale_question.png

Modify the code to produce the scale shown above.

import tkinter as tk

root = tk.Tk()
root.title("Scale Question")

value = tk.IntVar(value=10)

scale = tk.Scale(
    root,
    from_=0,
    to=20,
    orient="vertical",
    variable=value,
    length=100
)

scale.pack(padx=10, pady=10)

root.mainloop()

15.3. Methods

scale_widget.get()
Returns the current value of the scale.
scale_widget.set(value)
Sets the current value of the scale.
scale_widget.coords(value=None)
Returns the screen coordinates of the current slider position.
If value is supplied, returns the coordinates for that value.
scale_widget.identify(x, y)
Returns the name of the scale element at the specified coordinates.
scale_widget.flash()
Briefly flashes the widget several times.
Useful for drawing the user's attention to the widget.
scale_widget.invoke()
Invokes the scale's command callback, if one exists.

15.4. Control variable methods

variable.get()
Returns the current value stored in the control variable.
variable.set(value)
Sets the current value stored in the control variable.
The slider immediately moves to the specified position.

15.5. Parameter syntax

scale_widget = tk.Scale(parent, option=value)
parent is the window or frame object.
Options can be passed as parameters separated by commas.

Parameters:

activebackground
Syntax: scale_widget = tk.Scale(parent, activebackground="color")
Description: Sets the slider colour while it is being dragged.
Default: SystemButtonFace
Example: scale_widget = tk.Scale(root, activebackground="lightblue")
background
bg
Syntax: scale_widget = tk.Scale(parent, bg="color")
Description: Sets the background colour of the widget.
Default: SystemButtonFace
Example: scale_widget = tk.Scale(root, bg="white")
bd
Syntax: scale_widget = tk.Scale(parent, bd=width)
Description: Sets the width of the widget border.
Default: 2
Example: scale_widget = tk.Scale(root, bd=4)
borderwidth
Syntax: scale_widget = tk.Scale(parent, borderwidth=width)
Description: Sets the width of the widget border.
Default: 2
Example: scale_widget = tk.Scale(root, borderwidth=4)
command
Syntax: scale_widget = tk.Scale(parent, command=function)
Description: Calls a function whenever the slider is moved.
Example: scale_widget = tk.Scale(root, command=my_function)
cursor
Syntax: scale_widget = tk.Scale(parent, cursor="cursor_type")
Description: Sets the mouse cursor when hovering over the widget.
Default: arrow
Example: scale_widget = tk.Scale(root, cursor="hand2")
digits
Syntax: scale_widget = tk.Scale(parent, digits=value)
Description: Specifies the number of significant digits displayed for a StringVar.
Default: 0
font
Syntax: scale_widget = tk.Scale(parent, font=("font", size, style))
Description: Sets the font used for labels and values.
Default: TkDefaultFont
foreground
fg
Syntax: scale_widget = tk.Scale(parent, fg="color")
Description: Sets the text colour.
Default: SystemWindowText
from_
Syntax: scale_widget = tk.Scale(parent, from_=value)
Description: Sets the minimum value of the scale.
Default: 0
to
Syntax: scale_widget = tk.Scale(parent, to=value)
Description: Sets the maximum value of the scale.
Default: 100
rst id="w2kp8m"
label
Syntax: scale_widget = tk.Scale(parent, label="text")
Description: Displays a text label above a horizontal scale or beside a vertical scale.
Default: None
Example: scale_widget = tk.Scale(root, label="Volume")
length
Syntax: scale_widget = tk.Scale(parent, length=value)
Description: Sets the length of the scale in pixels.
Default: 100
Example: scale_widget = tk.Scale(root, length=250)
orient
Syntax: scale_widget = tk.Scale(parent, orient="horizontal")
Description: Specifies whether the scale is horizontal or vertical.
Valid values: "horizontal", "vertical"
Default: "vertical"
Example: scale_widget = tk.Scale(root, orient="horizontal")
relief
Syntax: scale_widget = tk.Scale(parent, relief="style")
Description: Sets the border style of the widget.
Default: flat
Example: scale_widget = tk.Scale(root, relief="groove")
repeatdelay
Syntax: scale_widget = tk.Scale(parent, repeatdelay=milliseconds)
Description: Specifies how long to wait before auto-repeating when the trough is held down.
Default: 300
Example: scale_widget = tk.Scale(root, repeatdelay=500)
repeatinterval
Syntax: scale_widget = tk.Scale(parent, repeatinterval=milliseconds)
Description: Specifies the time between repeated movements while the trough is held down.
Default: 100
Example: scale_widget = tk.Scale(root, repeatinterval=50)
resolution
Syntax: scale_widget = tk.Scale(parent, resolution=value)
Description: Sets the smallest increment between selectable values.
Default: 1
Example: scale_widget = tk.Scale(root, resolution=0.5)
showvalue
Syntax: scale_widget = tk.Scale(parent, showvalue=boolean)
Description: Determines whether the current value is displayed.
Default: 1
Example: scale_widget = tk.Scale(root, showvalue=0)
sliderlength
Syntax: scale_widget = tk.Scale(parent, sliderlength=value)
Description: Sets the length of the slider in pixels.
Default: 30
Example: scale_widget = tk.Scale(root, sliderlength=40)
sliderrelief
Syntax: scale_widget = tk.Scale(parent, sliderrelief="style")
Description: Sets the border style of the slider.
Default: raised
Example: scale_widget = tk.Scale(root, sliderrelief="sunken")
state
Syntax: scale_widget = tk.Scale(parent, state="state")
Description: Specifies whether the widget is enabled.
Valid values: "normal", "disabled"
Default: "normal"
Example: scale_widget = tk.Scale(root, state="disabled")
takefocus
Syntax: scale_widget = tk.Scale(parent, takefocus=1)
Description: Determines whether the widget can receive keyboard focus.
Default: 1
Example: scale_widget = tk.Scale(root, takefocus=0)
tickinterval
Syntax: scale_widget = tk.Scale(parent, tickinterval=value)
Description: Displays tick marks at the specified interval.
Default: 0 (no tick marks)
Example: scale_widget = tk.Scale(root, tickinterval=10)
troughcolor
Syntax: scale_widget = tk.Scale(parent, troughcolor="color")
Description: Sets the colour of the trough behind the slider.
Default: SystemButtonFace
Example: scale_widget = tk.Scale(root, troughcolor="lightgray")
variable
Syntax: scale_widget = tk.Scale(parent, variable=control_variable)
Description: Associates the scale with a control variable such as IntVar or DoubleVar.
Default: An internal Tcl variable.
Example: scale_widget = tk.Scale(root, variable=my_var)
width
Syntax: scale_widget = tk.Scale(parent, width=value)
Description: Sets the width of the trough in pixels.
Default: 15
Example: scale_widget = tk.Scale(root, width=25)

15.6. Default options

Code to display the default value for each Scale option is shown below.
import tkinter as tk

root = tk.Tk()

widget = tk.Scale(root)
widget_options = widget.keys()

for option in widget_options:
    print(f"{option}: {widget.cget(option)}")  # cget retrieves the current value of the option