1. tk command binding

1.1. Overview

In Tkinter, command binding allows you to connect a widget (such as a

button or slider) to a Python function. | When the user interacts with the widget (e.g., clicks a button), the linked function is executed. | This is essential for making your GUI interactive. | This is best for buttons, menus, scales, spinboxes

Many Tkinter widgets support the command option.

A callback function is called automatically when the user interacts with the widget.

The callback can then modify other widgets in the window.

---

1.2. Basic Syntax

The general syntax for command binding is:

widget = tk.Widget(parent, command=function_name)

Explanation:

• The command option is used to bind a function to the widget.

• Do NOT use parentheses () after the function name.

---

1.3. Example 1: Button Command Binding

import tkinter as tk


def change_text():
    label.config(text="Button pressed!")


# Create the main window
root = tk.Tk()
root.geometry("200x100")  # Set window size
root.title("Button -> label Example")  # Set window title

button = tk.Button(root, text="Click me", command=change_text)
button.pack(pady=10)

label = tk.Label(root, text="Waiting...")
label.pack(pady=10)

root.mainloop()

Explanation:

• The command option is used to bind change_text to the button.

• When the button is clicked, change_text runs.

• The label is updated with the new text.

---

1.4. Example 2: Using Lambda for Arguments

Sometimes you need to pass arguments to a function.

import tkinter as tk


def greet(name):
    label.config(text=f"Hello {name}.")


# Create the main window
root = tk.Tk()
root.geometry("200x100")  # Set window size
root.title("Button lambda -> label Example")  # Set window title

button = tk.Button(root, text="Click", command=lambda: greet("Alice"))
button.pack(pady=10)

label = tk.Label(root, text="Waiting...")
label.pack(pady=10)

root.mainloop()

Explanation:

• lambda creates an anonymous function.

• This allows passing arguments safely.

---

1.5. Example 3: Checkbutton Command Binding

tk.Checkbutton(..., command=function)

A Checkbutton calls the function whenever it is selected or deselected.

import tkinter as tk

root = tk.Tk()

selected = tk.IntVar()

def update():
    if selected.get():
        label.config(text="Checked")
    else:
        label.config(text="Unchecked")

check = tk.Checkbutton(
    root,
    text="Option",
    variable=selected,
    command=update
)

label = tk.Label(root, text="Unchecked")

check.pack()
label.pack()

root.mainloop()

---

tk.Radiobutton(..., command=function)

A Radiobutton calls the function whenever a different option is selected.

import tkinter as tk

root = tk.Tk()

choice = tk.StringVar(value="Red")

def update():
    label.config(text=choice.get())

tk.Radiobutton(
    root,
    text="Red",
    variable=choice,
    value="Red",
    command=update
).pack()

tk.Radiobutton(
    root,
    text="Blue",
    variable=choice,
    value="Blue",
    command=update
).pack()

label = tk.Label(root, text="Red")
label.pack()

root.mainloop()

---

tk.Scale(..., command=function)

A Scale passes the current slider value to the callback.

import tkinter as tk

root = tk.Tk()

def update(value):
    label.config(text=value)

scale = tk.Scale(
    root,
    from_=0,
    to=100,
    command=update
)

label = tk.Label(root, text="0")

scale.pack()
label.pack()

root.mainloop()

---

tk.Spinbox(..., command=function)

A Spinbox calls the function whenever the arrow buttons change the value.

import tkinter as tk

root = tk.Tk()

def update():
    label.config(text=spin.get())

spin = tk.Spinbox(
    root,
    from_=1,
    to=10,
    command=update
)

label = tk.Label(root, text="1")

spin.pack()
label.pack()

root.mainloop()

---

tk.OptionMenu(..., command=function)

An OptionMenu passes the selected option to the callback.

import tkinter as tk

root = tk.Tk()

selected = tk.StringVar(value="Apple")

def update(choice):
    label.config(text=choice)

menu = tk.OptionMenu(
    root,
    selected,
    "Apple",
    "Orange",
    "Pear",
    command=update
)

label = tk.Label(root, text="Apple")

menu.pack()
label.pack()

root.mainloop()

---

tk.Menubutton(...)

A Menubutton uses the commands of its attached Menu.

import tkinter as tk

root = tk.Tk()

def update():
    label.config(text="Green selected")

button = tk.Menubutton(root, text="Colours")

menu = tk.Menu(button, tearoff=0)
menu.add_command(label="Green", command=update)

button.config(menu=menu)

button.pack()

label = tk.Label(root, text="Waiting...")
label.pack()

root.mainloop()

---

tk.Scrollbar(..., command=widget.yview)

A Scrollbar usually controls another widget by calling one of its scrolling methods.

import tkinter as tk

root = tk.Tk()

text = tk.Text(root, width=20, height=5)

scrollbar = tk.Scrollbar(
    root,
    command=text.yview
)

text.config(yscrollcommand=scrollbar.set)

text.pack(side="left")
scrollbar.pack(side="right", fill="y")

root.mainloop()