app.py

# app.py

from flask import Flask, request, render_template

app = Flask(__name__)

def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

def multiply(a, b):
    return a * b

def divide(a, b):
    if b == 0:
        return "Error: Division by zero."
    return a / b

@app.route("/", methods=["GET", "POST"])
def calculator():
    result = None
    if request.method == "POST":
        try:
            num1 = float(request.form.get("num1"))
            num2 = float(request.form.get("num2"))
            operation = request.form.get("operation")
        
            if operation == "add":
                result = add(num1, num2)
            elif operation == "subtract":
                result = subtract(num1, num2)
            elif operation == "multiply":
                result = multiply(num1, num2)
            elif operation == "divide":
                result = divide(num1, num2)
        except ValueError:
            result = "Invalid input, please enter numbers only."
        
    return render_template("index.html", result=result)

if __name__ == "__main__":
    app.run(debug=True)