GUI Programming: Creating User Interfaces with Tkinter

1. Introduction to GUI (Graphical User Interface)

A GUI allows users to interact with a program using visual elements like windows, buttons, and text boxes, rather than just text commands. Tkinter is Python's standard GUI library. It is lightweight and included with Python by default (no pip install needed).

Basic Structure of a Tkinter Program:

1. Import: import tkinter as tk
2. Create Main Window: root = tk.Tk()
3. Configure Window: root.title("My App"), root.geometry("400x300")
4. Add Widgets: Labels, Buttons, Entry fields, etc.
5. Enter Main Loop: root.mainloop() (Keeps the window open and listening for events).

2. Tkinter Widgets

Widgets are the building blocks of a GUI.

3. Layout Managers (Geometry Management)

You must use a layout manager to place widgets in the window.

Rule: You CANNOT mix pack() and grid() in the same parent container. Choose one per Frame/Window.

4. Event Handling

GUI programming is event-driven — the program waits for user actions (clicks, key presses) and responds.

Methods to Handle Events:

Common Events:

• <Button-1> — Left mouse click
• <Return> — Enter key pressed
• <Key> — Any key pressed
• <FocusIn> / <FocusOut> — Widget gains/loses focus

5. Code Example (Grid Layout)

import tkinter as tk

root = tk.Tk()
root.title("Login")

# Row 0
tk.Label(root, text="Username").grid(row=0, column=0, padx=10, pady=5)
tk.Entry(root).grid(row=0, column=1, padx=10, pady=5)

# Row 1
tk.Label(root, text="Password").grid(row=1, column=0, padx=10, pady=5)
tk.Entry(root, show="*").grid(row=1, column=1, padx=10, pady=5)

# Row 2
tk.Button(root, text="Login", command=lambda: print("Logged in!")).grid(row=2, column=0, columnspan=2, pady=10)

root.mainloop()