Tkinter Combobox: Item Management and Customization

In this tutorial, we’ll learn various aspects of Combobox in Tkinter, starting with the use of the postcommand attribute which allows dynamic updating of the widget’s contents.

We’ll also cover methods to retrieve the number of items in the Combobox using methods like the len() function and cget() method.

 

 

Combobox postcommand

The postcommand option allows you to specify a function or a method that will be called each time the drop-down list of the Combobox is about to be displayed.

You can use it if you want the contents of the Combobox to be dynamically updated right before the user sees the drop-down list.

import tkinter as tk
from tkinter import ttk
def update_combobox_options():
    options = ["Option 1", "Option 2", "Option 3"]
    combobox['values'] = options
root = tk.Tk()
combobox = ttk.Combobox(root, postcommand=update_combobox_options)
combobox.pack()
root.mainloop()

Output:

 

Get Number of Items

Using len() Function

You can use the len() function on the Combobox’s values.

import tkinter as tk
from tkinter import ttk
root = tk.Tk()
combobox = ttk.Combobox(root)
combobox['values'] = ('Item 1', 'Item 2', 'Item 3')
number_of_items = len(combobox['values'])
print("Number of items in the combobox:", number_of_items)
root.mainloop()

Output:

Number of items in the combobox: 3

Using cget() Method

The cget() method of the Combobox widget allows you to retrieve the values and then you can calculate the length using len().

number_of_items = len(combobox.cget('values'))

 

Check If Combobox Is Empty

You can use the len() function on the values of the Combobox. If the length is 0, it means the Combobox is empty.

import tkinter as tk
from tkinter import ttk
root = tk.Tk()
combobox = ttk.Combobox(root)
combobox['values'] = ('Item 1', 'Item 2', 'Item 3')
is_empty = len(combobox['values']) == 0
print("Is the combobox empty?", is_empty)
root.mainloop()

Output:

Is the combobox empty? False

 

Adjust Dropdown Size

You can adjust Tkinter combobox dropdown size by configuring the height property of the Combobox widget.

This property determines the number of items visible in the dropdown list at once.

import tkinter as tk
from tkinter import ttk
sample_data = ["Option 1", "Option 2", "Option 3", "Option 4", "Option 5"]
root = tk.Tk()
root.title("Adjust Combobox Dropdown Size")
combobox = ttk.Combobox(root, values=sample_data)
combobox.config(height=5)  # Adjust dropdown size here
combobox.pack()
root.mainloop()

Output:

 

Change Current Text

To change the current text of a Tkinter Combobox in Python, you can use the set method of the Combobox widget.

import tkinter as tk
from tkinter import ttk
plan_options = ["Plan A", "Plan B", "Plan C"]
root = tk.Tk()
root.geometry("300x200")
combobox = ttk.Combobox(root, values=plan_options)
combobox.pack(pady=20)
combobox.set("Plan B")
root.mainloop()

 

Change Font Size

You can use the option_add to modify the font properties for specific widget elements using a combination of wildcards and element names.

from tkinter import ttk
import tkinter as tk
custom_font = ("Verdana", 12)
root = tk.Tk()
root.option_add("*TCombobox*Listbox.font", custom_font)
combobox1 = tk. ttk.Combobox(root, values=["Option A", "Option B"])
combobox1.pack()
combobox2 = tk. ttk.Combobox(root, values=["Choice 1", "Choice 2"])
combobox2.pack()
root.mainloop()

Output:

All comboboxes now have bigger font sizes.