Python GUI apps with Tkinter and office automation

GUIs and automation

A GUI (graphical user interface) is a program with windows, buttons and text boxes instead of a black terminal. Automation means letting Python do repetitive office work: filling Excel sheets, making certificates or renaming hundreds of files.

Tkinter comes with Python on Windows, so a GUI needs nothing extra to install.

Your first Tkinter window

import tkinter as tk

root = tk.Tk()
root.title("My First App")
root.geometry("300x150")          # width x height in pixels

tk.Label(root, text="Hello, Tkinter!", font=("Arial", 14)).pack(pady=20)

root.mainloop()                   # show the window and wait for clicks

mainloop() must be the last line: it keeps the window open and responds to the user until the window is closed.

Common widgets

Layout managers: pack and grid

• pack() stacks widgets one after another, top to bottom by default.
• grid(row=, column=) places widgets in rows and columns, like a table. It suits forms best.

Do not mix pack and grid in the same window or frame.

Read inputs, calculate, show the result

import tkinter as tk

def calculate():
    try:
        bill = float(bill_box.get())
        tip = bill * 0.10
        result.config(text=f"Tip: Rs {tip:.2f}   Total: Rs {bill + tip:.2f}")
    except ValueError:
        result.config(text="Please enter a number")

root = tk.Tk()
root.title("Tip Calculator")
tk.Label(root, text="Bill amount").grid(row=0, column=0, padx=8, pady=8)
bill_box = tk.Entry(root)
bill_box.grid(row=0, column=1, padx=8)
tk.Button(root, text="Calculate", command=calculate).grid(row=1, column=0, columnspan=2)
result = tk.Label(root, text="")
result.grid(row=2, column=0, columnspan=2, pady=8)
root.mainloop()

• entry.get() reads what was typed (always a string).
• command=calculate passes the function without brackets; Tkinter calls it on each click.
• label.config(text=...) changes what a label shows.

Timers with after()

Never use time.sleep() in a GUI: it freezes the window. Use after(milliseconds, function) to run a function later:

seconds = 0

def tick():
    global seconds
    seconds += 1
    clock.config(text=str(seconds))
    root.after(1000, tick)        # run tick again in 1 second

root = tk.Tk()
clock = tk.Label(root, text="0", font=("Arial", 32))
clock.pack(padx=40, pady=20)
root.after(1000, tick)
root.mainloop()

Automating Excel with openpyxl

from openpyxl import Workbook, load_workbook     # pip install openpyxl

wb = Workbook()
ws = wb.active
ws.title = "Marks"
ws.append(["Name", "Marks"])                     # one row
for row in [("Asha", 91), ("Ravi", 78)]:
    ws.append(row)
ws["D1"] = "Average"
ws["D2"] = "=AVERAGE(B2:B3)"                     # a real Excel formula
wb.save("marks.xlsx")

wb = load_workbook("marks.xlsx")
for name, marks in wb["Marks"].iter_rows(min_row=2, values_only=True):
    print(name, marks)

Generate certificates with Pillow

from PIL import Image, ImageDraw, ImageFont      # pip install pillow

for name in ["Asha Kumari", "Ravi Kumar"]:
    img = Image.open("certificate_template.png")
    draw = ImageDraw.Draw(img)
    font = ImageFont.truetype("arial.ttf", 60)
    draw.text((600, 420), name, font=font, fill="navy", anchor="mm")
    img.save(f"certificates/{name}.png")

One loop makes a certificate for every student in a list or an Excel sheet.

Rename hundreds of files in one go

from pathlib import Path

for i, photo in enumerate(sorted(Path("photos").glob("*.jpg")), start=1):
    photo.rename(photo.with_name(f"trip_{i:03}.jpg"))     # trip_001.jpg, trip_002.jpg ...

Test a renaming script on a copy of the folder first: a mistake renames every file at once.

Common mistakes

• Writing command=calculate(): the brackets call the function once at start-up instead of on each click.
• Forgetting mainloop(), so the window flashes and closes.
• Using time.sleep() inside a GUI, which freezes it.
• Forgetting wb.save(...) after changing an Excel workbook.

Key points

• tk.Tk() makes a window; widgets are placed with pack() or grid(); mainloop() runs it.
• Buttons take command=function without brackets; entry.get() reads input.
• after() schedules work without freezing the window.
• openpyxl, Pillow and pathlib automate Excel, images and files.

Practice questions

ws["A10"] = "Total"
wb.save("report.xlsx")