Calc.py

#!/usr/bin/python
#Module: Calc.py (a.k.a. Calcul8.py)
#Purpose: Calculator program
#Language: Python 2.7
#Author: Chris Clarke
#Date: 24.08.2014

import sys

def calc(first, operator, second):
    ans = 0
    if operator == '+':
        ans = first + second
    elif operator == '-':
        ans = first - second
    elif operator in {'*', 'x', 'X'}:
        ans = first * second
    elif operator == '/':
        if second != 0:
            ans = first / second
        else:
            print_error("Can't divide by zero!")
    elif operator == '%':
        if second != 0:
            ans = first % second
        else:
            print_error("Can't do modulo zero!")
    elif operator == '^' or  operator == '**':
        ans = first ** second
    return ans

def print_error(error):
    print error
    sys.exit(1)

def get_number(message):
    while True:
        try:
            number = float(raw_input(message))
        except ValueError:
            print "Not a number"
        else:
            return number

title =  "*** Calc u L8r! ***"

print title
first = get_number("Enter first number: ")
first_time = True
while True:
    if first_time:
        prompt = "Enter operator (+,-,*,/,%,^): "
        first_time = False
    else:
        prompt = "Enter operator (+,-,*,/,%,^,(n)ew,(q)uit): "
    operator = raw_input(prompt)
    if operator in {'n', 'new'}:
        first = 0.0
        print "\nResult:", first
        first = get_number("Enter first number: ")
        continue
    if operator in {'q', 'quit'}:
        print "Quitting program..."
        print title
        break
    if not operator in {'+','-','*','x','X','/','%','^','**'}:
        print "Invalid operator!"
        continue
    second = get_number("Enter second number: ")
    first = calc(first, operator, second)
    print "\nResult:", first