Tkinter DoubleVar

Summary: In this tutorial, you’ll learn how to use the Tkinter DoubleVar objects to link widgets with Python variables.

Introduction to the Tkinter DoubleVar #

In Tkinter, the DoubleVar class allows you to create float variable objects.

A DoubleVar object holds an float value. Tkinter links an DoubleVar object with a widget, such as an Entry or Scale. Through DoubleVar objects, you can dynamically handle the widget’s values.

Creating DoubleVar objects #

To create a DoubleVar object, you can follow these steps:

First, import the tkinter module:

import tkinter as tkCode language: Python (python)

Second, create a new DoubleVar object:

amount_var = tk.DoubleVar()Code language: Python (python)

Note that the DoubleVar() constructor has three optional parameters:

• master is the master widget.
• value is an initial value that defaults to 0.0 .
• name is an optional Tcl name that defaults to PY_VARnum.

Linking DoubleVar objects with widgets #

The following shows how to associate a DoubleVar object with a widget (Entry):

amount_entry = ttk.Entry(root, textvariable=amount_var)Code language: Python (python)

Accessing and Changing DoubleVar Value #

If a DoubleVar object associates with a widget, you can get the current value of the widget using the get() method:

current_value = double_var.get()Code language: Python (python)

Additionally, you can change the value of the widget via the DoubleVar object using the set function:

double_var.set(20)Code language: Python (python)

Tracing Values #

To automatically execute a function when the value of an DoubleVar changes, you can use the trace_add method:

double_var.trace_add(mode, callback)Code language: Python (python)

The trace_add() method accepts two parameters:

• mode: Determines when the DoubleVar object should execute the callback function. The mode can be 'write', 'read', and 'unset', or a tuple of these strings. For example, if you set the mode to 'write', the DoubleVar object will execute the callback when its value changes.
• callback: A function that the DoubleVar will execute according to the mode.

If you want to stop tracing values, you can use the trace_remove() method:

double_var.trace_remove(mode, callback)Code language: Python (python)

The trace_remove() method removes the callback from executing for specified modes.

Using DoubleVar with Entry Widgets #

The following program shows how to use an DoubleVar object with the entry widget:

import tkinter as tk
from tkinter import ttk
from tkinter.messagebox import showinfo


root = tk.Tk()
root.geometry('400x300')
root.title('DoubleVar Demo')


amount_var = tk.DoubleVar()

label = ttk.Label(root, text='Amount:')
label.pack(side=tk.LEFT, padx=5, pady=10, anchor=tk.W)   

amount_entry = ttk.Entry(root, textvariable=amount_var)
amount_entry.pack(side=tk.LEFT, padx=5, pady=10, anchor=tk.W)


button = ttk.Button(
    root, 
    text='Submit', 
    command=lambda: showinfo(title='Amount', message=amount_var.get()))

button.pack(side=tk.LEFT, padx=5, pady=10, anchor=tk.W)


root.mainloop()Code language: Python (python)

How the program works:

First, create a new DoubleVar object:

amount_var = tk.DoubleVar()Code language: Python (python)

Second, link the DoubleVar object with an Entry widget:

amount_entry = ttk.Entry(root, textvariable=amount_var)Code language: Python (python)

Third, show the current value of the entry widget via the amount_var object when the button is clicked:

button = ttk.Button(
    root, 
    text='Submit', 
    command=lambda: showinfo(title='Amount', message=amount_var.get())
)Code language: Python (python)

Summary #

• Use the DoubleVar class to create float variable objects.
• Associate DoubleVar objects with widgets to manage float values.