Make a Simple Calculator - Python

Last Updated : 12 Apr, 2025

In this article, we will create a simple calculator that can perform basic arithmetic operations like addition, subtraction, multiplication and division. We will explore two implementations for the same:

  • Command-Line Calculator
  • GUI-Based Calculator using Tkinter

Command-Line Calculator

This version of the calculator takes user input and performs operations based on the selected option.

Python 
def add(n1, n2):
    return n1 + n2

def sub(n1, n2):
    return n1 - n2

def mul(n1, n2):
    return n1 * n2

def div(n1, n2):
    return n1 / n2

print("Please select operation -\n"
      "1. Add\n"
      "2. Subtract\n"
      "3. Multiply\n"
      "4. Divide\n")

sel = int(input("Select operation (1-4): "))

n1 = int(input("Enter first number: "))
n2 = int(input("Enter second number: "))

if sel == 1:
    print(n1, "+", n2, "=", add(n1, n2))
elif sel == 2:
    print(n1, "-", n2, "=", sub(n1, n2))
elif sel == 3:
    print(n1, "*", n2, "=", mul(n1, n2))
elif sel == 4:
    print(n1, "/", n2, "=", div(n1, n2))
else:
    print("Invalid input")

Output:

Please select operation -
1. Add
2. Subtract
3. Multiply
4. Divide

Select operation (1-4): 1
Enter first number : 15
Enter second number : 14
15 + 14 = 29

Explanation:

  • Function Definitions: add(), subtract(), multiply() and divide() perform their respective mathematical operations.
  • User Menu Display: Prints a menu with four arithmetic operations.
  • User Input: Takes operation choice (1-4) and two numbers.
  • Conditional Execution: Calls the corresponding function based on user input and prints the result.
  • Invalid Selection Handling: Displays "Invalid input" if the user enters an incorrect option.

GUI-Based Calculator using Tkinter

The graphical calculator will have an interactive interface allowing users to perform calculations using buttons.

Features:

  • A user-friendly interface.
  • Supports basic arithmetic operations.
  • Displays results instantly.
  • Error handling for incorrect inputs.

Installing Tkinter:

Tkinter comes pre-installed with Python. If not, install it using:

pip install tk

Python 
import tkinter as tk
import tkinter.messagebox
from tkinter.constants import SUNKEN

win = tk.Tk()
win.title('Calculator')

frame = tk.Frame(win, bg="skyblue", padx=10)
frame.pack()

entry = tk.Entry(frame, relief=SUNKEN, borderwidth=3, width=30)
entry.grid(row=0, column=0, columnspan=3, ipady=2, pady=2)

def click(num):
    entry.insert(tk.END, num)

def equal():
    try:
        res = str(eval(entry.get()))
        entry.delete(0, tk.END)
        entry.insert(0, res)
    except:
        tk.messagebox.showinfo("Error", "Syntax Error")

def clear():
    entry.delete(0, tk.END)

buttons = [
    ('1', 1, 0), ('2', 1, 1), ('3', 1, 2),
    ('4', 2, 0), ('5', 2, 1), ('6', 2, 2),
    ('7', 3, 0), ('8', 3, 1), ('9', 3, 2),
    ('0', 4, 1), ('+', 5, 0), ('-', 5, 1),
    ('*', 5, 2), ('/', 6, 0)
]

for txt, r, c in buttons:
    tk.Button(frame, text=txt, padx=15, pady=5, width=3, command=lambda t=txt: click(t)).grid(row=r, column=c, pady=2)

tk.Button(frame, text="Clear", padx=15, pady=5, width=12, command=clear).grid(row=6, column=1, columnspan=2, pady=2)
tk.Button(frame, text="=", padx=15, pady=5, width=9, command=equal).grid(row=7, column=0, columnspan=3, pady=2)

win.mainloop()

Output:

Calculator GUI
Calculator Working
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