# -*- coding: utf-8 -*-
"""
--------------------------------------------------------------------------
Simple Calculator
--------------------------------------------------------------------------
License:
Copyright 2018 FRANCISCO MONTANO

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
    
1.  Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.

2.  Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.

3.  Neither the name of the copyright holder nor the names of its contributors
may be used to endorse or promote products derived from this software without
specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
THE POSSIBILITY OF SUCH DAMAGE.
--------------------------------------------------------------------------

Simple calculator that will
    -  Take in two numbers from the user
    -  Take in an operator from the user
    -  Perform the mathematical operation and provide the number to the user
    -  Repeat

Operations:
    -  addition
    -  subtraction
    -  multiplication
    -  division

Error conditions:
    -  Invalid operator --> Program should exit
    -  Invalid number   --> Program should exit

--------------------------------------------------------------------------
"""
import operator

# ------------------------------------------------------------------------
# Constants
# ------------------------------------------------------------------------

operators = {
    "+"  : operator.add,
    "-"  : operator.sub,
    "*"  : operator.mul,
    "/"  : operator.truediv, 
    ">>" : operator.rshift,
    "<<" : operator.lshift,
    "%"  : operator.mod,
    "**" : operator.pow
}

# ------------------------------------------------------------------------
# Global variables
# ------------------------------------------------------------------------

# ------------------------------------------------------------------------
# Functions
# ------------------------------------------------------------------------

def get_user_input():
    try:
        number1 = int(input("Enter the first integer:  "))
        number2 = int(input("Enter the second integer: "))
        op      = input("Enter an operator (valid operators are +, -, *, /, >>, <<, %, and **): ")

        return (number1, number2, op)
    except:
        print("Invalid Input!")
        return (None, None, None)

# ------------------------------------------------------------------------
# Main script
# ------------------------------------------------------------------------

if __name__ == "__main__":

    # Bind input to try_input so code works on Python 2
    try:
        input = raw_input
    except NameError:
        pass

    while True:
        (number1, number2, op) = get_user_input()

        func = operators.get(op, None)    

        if (number1 is None) or (number2 is None) or (func is None):
            print("Quitting.")
            break
        else:
            print(func(number1, number2))
