calculator_with_history.py

import os
import re

HISTORY_FILE = "history.txt"


def show_history():
    if not os.path.exists(HISTORY_FILE):
        print("No history found!")
        return

    with open(HISTORY_FILE, 'r') as file:
        lines = file.readlines()

    if not lines:
        print("No history found!")
    else:
        for line in reversed(lines):
            print(line.strip())


def clear_history():
    with open(HISTORY_FILE, 'w'):
        pass
    print("History cleared.")


def saveto_history(equation, result):
    with open(HISTORY_FILE, 'a') as file:
        file.write(f"{equation} = {result}\n")


def calculate(user_input):
    # Allow input like 2+2 by adding spaces automatically
    user_input = re.sub(r'(\d)([+\-*/])(\d)', r'\1 \2 \3', user_input)

    parts = user_input.split()
    if len(parts) != 3:
        print("Invalid input! USE FORMAT: number operator number (i.e. 8 + 8)")
        return

    try:
        num1 = float(parts[0])
        op = parts[1]
        num2 = float(parts[2])
    except ValueError:
        print("Invalid numbers.")
        return

    if op == "+":
        result = num1 + num2
    elif op == "-":
        result = num1 - num2
    elif op == "*":
        result = num1 * num2
    elif op == "/":
        if num2 == 0:
            print("Cannot divide by zero.")
            return
        result = num1 / num2
    else:
        print("Invalid operator. USE ONLY +, -, *, /.")
        return

    if result.is_integer():
        result = int(result)

    print("RESULT:", result)
    saveto_history(user_input, result)


def main():
    print("--- SIMPLE CALCULATOR (type history, clear or exit) ---")

    while True:
        user_input = input(
            "Enter calculation (+ - * /) OR command (history, clear, exit): "
        ).strip().lower()

        if user_input == 'exit':
            print("Goodbye!")
            break
        elif user_input == 'history':
            show_history()
        elif user_input == 'clear':
            clear_history()
        else:
            calculate(user_input)


if __name__ == "__main__":
    main()