A calculator with functions in Python.

The program

Press Run to see what it prints. Change anything you like, then run it again.

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 "Cannot divide by zero"
    return a / b

operations = {"+": add, "-": subtract, "*": multiply, "/": divide}

for a, op, b in [(8, "+", 5), (9, "-", 4), (6, "*", 7), (20, "/", 4), (5, "/", 0)]:
    print(a, op, b, "=", operations[op](a, b))

8 + 5 = 13
9 - 4 = 5
6 * 7 = 42
20 / 4 = 5.0
5 / 0 = Cannot divide by zero

How it works

1. Each function takes two parameters and returns an answer. The divide function checks for zero first, because dividing by zero is an error.
2. A dictionary pairs a key (the symbol) with a value (the function). operations[op] looks up the function, and the brackets after it call it.
3. Functions are values in Python, so you can store them in dictionaries and lists.

Try this

• Add a power operation with **.
• Add a remainder operation with %.
• Test your own pairs of numbers.

Stuck on an error? Read how to debug Python.