Simple Terminal Calculator

The goal for this chapter, is to go through a more exhaustive Python program to act as base for the next chapter, testing our own code.

The source code (and resources for later chapters in this tutorial) is also available at: https://github.com/road-to-cloud/chapter-2-python-github

As this shall not function as a sole Python tutorial, we will not go into the details of what, how and why, but here is a sample code for a simple terminal calculator:

We define our supported operations as follows in the operations.py script:

operations.py

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

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

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

def division(a, b):
    return a / b

We implement a Calculator class that acts as a controller for the operations in the calculator.py script and takes over the user input, parsing and interpreting:

calculator.py

from typing import Union
from operations import addition, subtraction, multiplication, division


class Calculator():

    def input_equation(self) -> Union[str, str, str]:
        equation: str = input("Enter an equation:\n")
        return equation.split(" ")

    def interprete_equation(self, equation: str) -> Union[float, str, float]:
        a = int(equation[0])
        b = int(equation[2])
        operator = equation[1]
        return [a, operator, b]

    def operation(self) -> str:
        operation: Union[str, str, str] = self.input_equation()

        print(f"Calculating: {' '.join(operation)} ...")
        a, operand, b = self.interprete_equation(operation)

        match operand:
            case "+":
                return f"{a} + {b} = {addition(a, b)}"
            case "-":
                return f"{a} - {b} = {subtraction(a, b)}"
            case "*":
                return f"{a} * {b} = {multiplication(a, b)}"
            case "/":
                return f"{a} / {b} = {division(a, b)}"
            case _:
                return "Invalid operator"

Finally, the main.py script acts as the entry point for the program, and its sole job is to instantiate the Calculator class and infinitely loop through its operation method:

main.py

from calculator import Calculator

def main():
    calculator = Calculator()

    while (True):
        try:
            print(calculator.operation())
        except ValueError:
            print("\nInvalid input, try again\n")


if __name__ == "__main__":
    main()