Why does a tkinter scale widget require a tkinter variable

Question

I understand that you don't need a variable to be specified for a scale like such:

scale = tk.Scale(root, from_ = 1, to = 100) # makes scale without variable
scaleValue = scale.get() # sets value to scale

I, however, need a way to have a variable set in real time and every time the scale value is changed. Is there a way to make that work without constantly resetting scaleValue to scale.get()?

Answer 1

If you use something like an IntVar() to track the value you can see that it is auto updated with a function that will check the current value.

If you want the value to be displayed and returned as a float you can use DoubleVar() and then also set resolution=0.01 as an argument in the Scale widget.

import tkinter as tk

class Example(tk.Tk):
    def __init__(self):
        super().__init__()
        self.int_var = tk.IntVar()
        self.scale = tk.Scale(self, from_=1, to=100, variable=self.int_var)
        self.scale.pack()

        tk.Button(self, text="Check Scale", command=self.check_scale).pack()

    def check_scale(self):
        print(self.int_var.get())


if __name__ == "__main__":
    Example().mainloop()

Results:

For an example using the DoubleVar() you can do this:

import tkinter as tk

class Example(tk.Tk):
    def __init__(self):
        super().__init__()
        self.dou_var = tk.DoubleVar()
        self.scale = tk.Scale(self, from_=1, to=100, resolution=0.01, variable=self.dou_var)
        self.scale.pack()

        tk.Button(self, text="Check Scale", command=self.check_scale).pack()

    def check_scale(self):
        print(self.dou_var.get())


if __name__ == "__main__":
    Example().mainloop()

Results:

Answer 2

By making a tkinter variable using variable = tk.DoubleVar(), it will automatically update variable when a change has happened.

scaleVar = tk.DoubleVar
scale = tk.Scale(
    root,
    from_ = 1,
    to = 100,
    variable = scaleVar    # makes scale with updating variable
)