How to Build a Digital Clock in Python Tkinter

Creating a digital clock is an excellent way to learn the basics of GUI programming in Python. This guide will walk you through building a desktop application using the tkinter library. The application will feature a live clock, current date display, and a toggle button to switch between 12-hour and 24-hour formats.

Prerequisites

We will use tkinter for the interface and ttkthemes to improve the visual style.

First, install the necessary libraries:

sudo apt-get install python3-tk -y
pip install ttkthemes

Step 1: Imports and Setup

Create a file named digital_clock.py. We begin by importing tkinter, styling modules, and the time formatting function.

import tkinter as tk
from tkinter import ttk
from ttkthemes import ThemedStyle
from time import strftime

Step 2: Defining the Logic

We need two core functions:

1. time(): Fetches the current time, updates the label, and schedules itself to run again in 1 second.
2. toggle_time_format(): Switches the global flag between 12-hour and 24-hour modes.

# Global variable to track format
is_24_hour_format = True

def toggle_time_format():
    """Switches between 12-hour and 24-hour formats."""
    global is_24_hour_format
    is_24_hour_format = not is_24_hour_format
    # Update button text to show what the NEXT click will do
    time_format_button.config(text="12 Hour" if is_24_hour_format else "24 Hour")

def time():
    """Updates the time and date labels every second."""
    # Determine format string based on flag
    # %H = 24h hour, %I = 12h hour, %p = AM/PM
    current_time_format = "%H:%M:%S" if is_24_hour_format else "%I:%M:%S %p"
    
    current_time = strftime(current_time_format)
    current_date = strftime("%A, %B %d, %Y")
    
    # Update labels
    label_time.config(text=current_time)
    label_date.config(text=current_date)
    
    # Schedule next update in 1000ms (1 second)
    label_time.after(1000, time)

Step 3: Creating the GUI

We initialize the main window, apply a theme, and arrange our widgets (Labels and Button) using a Frame.

# 1. Main Window Setup
root = tk.Tk()
root.title("Digital Clock")
root.geometry("400x250")

# 2. Styling
style = ThemedStyle(root)
style.set_theme("plastik")  # Options: plastik, arc, radiance, etc.

# Configure colors and fonts
# 'TLabel' and 'TButton' are standard ttk widget class names
style.configure("TLabel", foreground="#FF5733", background="#333333")
style.configure("TButton", foreground="#FF5733", background="#333333", font=("calibri", 10, "bold"))
style.configure("TFrame", background="#333333")

# 3. Layout
# Create a central frame to hold everything
frame = ttk.Frame(root, style="TFrame", padding=20)
frame.place(relx=0.5, rely=0.5, anchor="center")

# Time Label (Large font)
label_time = ttk.Label(frame, font=("calibri", 48, "bold"))
label_time.pack()

# Date Label (Smaller font)
label_date = ttk.Label(frame, font=("calibri", 16))
label_date.pack()

# Toggle Button
time_format_button = ttk.Button(
    frame, 
    text="12 Hour", 
    command=toggle_time_format, 
    style="TButton"
)
time_format_button.pack(pady=20)

note

Using label_time.after(1000, time) is crucial. Tkinter is event-driven; using a standard while True loop with time.sleep() would freeze the GUI. The .after() method registers a callback to run later without blocking the interface.

Step 4: Running the Application

Finally, trigger the first update manually and start the main event loop.

# Initial call to start the clock
time()

# Start the application
root.mainloop()

To run the application:

python digital_clock.py

Conclusion

You have successfully built a GUI application in Python.

1. tk.Tk() creates the main window.
2. root.mainloop() keeps the window open and listening for events.
3. widget.after() allows for periodic updates (like a clock tick) without freezing the UI.
4. strftime provides flexible string formatting for time and date objects.