Python Calculator – CLI Project

import math
import operator

class Calculator:
    OPERATIONS = {
        "+": operator.add, "-": operator.sub,
        "*": operator.mul, "/": operator.truediv,
        "**": operator.pow, "%": operator.mod,
    }

    def __init__(self):
        self.history = []

    def calculate(self, a, op, b):
        if op not in self.OPERATIONS:
            raise ValueError(f"Unknown operator: {op}")
        if op == "/" and b == 0:
            raise ZeroDivisionError("Cannot divide by zero")
        result = self.OPERATIONS[op](a, b)
        self.history.append(f"{a} {op} {b} = {result}")
        return result

    def sqrt(self, n):
        if n < 0:
            raise ValueError("Cannot take sqrt of negative number")
        result = math.sqrt(n)
        self.history.append(f"sqrt({n}) = {result}")
        return result

def main():
    calc = Calculator()
    print("Python Calculator  |  ops: + - * / ** %  |  sqrt   |  history  |  quit")
    while True:
        try:
            expr = input("> ").strip().lower()
            if expr == "quit": break
            if expr == "history":
                print("\n".join(f"  {i+1}. {e}" for i, e in enumerate(calc.history)) or "No history.")
                continue
            if expr.startswith("sqrt "):
                print(calc.sqrt(float(expr[5:])))
                continue
            parts = expr.split()
            if len(parts) == 3:
                a, op, b = float(parts[0]), parts[1], float(parts[2])
                print(calc.calculate(a, op, b))
            else:
                print("Format:   ")
        except (ValueError, ZeroDivisionError) as e:
            print(f"Error: {e}")
        except KeyboardInterrupt:
            break

if __name__ == "__main__":
    main()

python calculator.py
# > 5 + 3       → 8.0
# > sqrt 16     → 4.0
# > history