How to create a calculator using Python

Python is a versatile and powerful programming language that can be used for many applications, including creating a calculator. In this blog post, we will learn how to create a simple calculator using Python that can perform basic arithmetic operations such as addition, subtraction, multiplication and division.

To create a calculator using Python, we will need to use some built-in modules and functions. The modules we will use are:

- sys: This module provides access to some system-specific parameters and functions, such as command-line arguments and exit status.
- math: This module provides access to some mathematical functions and constants, such as pi and square root.
- tkinter: This module provides a graphical user interface (GUI) toolkit for Python, which allows us to create windows, buttons, labels and other widgets.

The functions we will use are:

- eval: This function evaluates a string as a Python expression and returns the result. For example, eval("2+3") returns 5.
- str: This function converts any object to a string representation. For example, str(5) returns "5".
- lambda: This is a keyword that allows us to create anonymous functions, which are functions that are not bound to a name. For example, lambda x: x+1 is a function that takes one argument x and returns x+1.

The steps we will follow to create a calculator using Python are:

1. Import the modules we need.
2. Create a window using tkinter and give it a title and a size.
3. Create a label widget to display the expression and the result of the calculation.
4. Create a string variable to store the expression entered by the user.
5. Create a function to update the label with the expression and the result.
6. Create a function to clear the expression and the result.
7. Create a function to append a character to the expression.
8. Create a function to evaluate the expression and display the result.
9. Create buttons for each digit, operator and function (clear and equal) and bind them to their respective functions.
10. Arrange the widgets in a grid layout using tkinter.

python

# Import modules

import sys

import math

import tkinter as tk

# Create window

window = tk.Tk()

window.title("Calculator")

window.geometry("300x300")

# Create label

label = tk.Label(window, text="0", font=("Arial", 20))

label.grid(row=0, column=0, columnspan=4)

# Create string variable

expression = tk.StringVar()

expression.set("")

# Create update function

def update():

    # Get the expression

    expr = expression.get()

    # Try to evaluate the expression

    try:

        # Evaluate the expression using eval function

        result = eval(expr)

        # Update the label with the expression and the result

        label.config(text=expr + "\n" + str(result))

    # If there is an error, display it

    except Exception as e:

        # Update the label with the error message

        label.config(text=str(e))

# Create clear function

def clear():

    # Clear the expression

    expression.set("")

    # Update the label

    update()

# Create append function

def append(char):

    # Get the current expression

    expr = expression.get()

    # Append the character to the expression

    expr += char

    # Set the new expression

    expression.set(expr)

    # Update the label

    update()

# Create evaluate function

def evaluate():

    # Get the current expression

    expr = expression.get()

    # Try to evaluate the expression

    try:

        # Evaluate the expression using eval function

        result = eval(expr)

        # Set the new expression as the result

        expression.set(str(result))

        # Update the label

        update()

    # If there is an error, display it

    except Exception as e:

        # Update the label with the error message

        label.config(text=str(e))

# Create buttons

buttons = [

    ["7", "8", "9", "+"],

    ["4", "5", "6", "-"],

    ["1", "2", "3", "*"],

    ["0", ".", "C", "/"],

    ["(", ")", "=", "exit"]

]

# Loop through buttons and create them

for i in range(len(buttons)):

    for j in range(len(buttons[i])):

        # Get the button text

        text = buttons[i][j]

        # Create a button with the text and a size of 5x2

        button = tk.Button(window, text=text, width=5, height=2)

        # Place the button in the grid layout at row i+1 and column j

        button.grid(row=i+1, column=j)

        # Bind different functions to different buttons

        if text == "C":

            # Bind the clear function to the button

            button.config(command=clear)

        elif text == "=":

            # Bind the evaluate function to the button

            button.config(command=evaluate)

        elif text == "exit":

            # Bind the exit function to the button

            button.config(command=sys.exit)

        else:

            # Bind the append function with the text as an argument to the button

            button.config(command=lambda char=text: append(char))

# Start the main loop of the window

window.mainloop()