# File name: MyEquationCalculator.py
# Author: Daven Lin
# Date created: 1/27/2016
# Date last modified: 1/27/2016
# Python Version: 3.4.3

print("\nWelcome to My Equation Calculator")
print("\nThe equation you enter must follow this syntax:"
"\n<operand><space><operator_entered_as_a_string><space><operand>")

# Set variables
opList = ["plus", "minus", "times", "divided-by", "equals"]

# Read user's equation as a string
equation = input("\nPlease, enter your equation by following the syntax expressed above: ")

# define functions
def plus(x,y):
    z = x + y
    print(z)

def minus(x,y):
    z = x - y
    print(z)

def times(x,y):
    z = x * y
    print(z)

def divide(x,y):
    x = float(x)
    y = float(y)
    z = x / y
    print(z)


# Echo to the screen what the user has entered
print('The equation you entered is "%s".' %equation,)

# Parse the equation into a list
theParts = equation.split()


if len(theParts) == 0 :
    print("\nHave you simply pressed the Enter key? Please, enter an equation next time! :)")

elif len(theParts) == 1 :
    print('\nYou have enetered the equation "%s"' %equation, end= " ")
    print("which is not a complete and valid equation")
    print('since it contains a sequence of letters which are not operands nor operator. Please, try again.')

elif len(theParts) == 2 :
    print('\nYou have enetered the equation "%s"' %equation, end= " ")
    print("which is not a complete and valid equation")
    print('since it contains the operator "%s"' %equation, end=" ")
    print('Please, try again.')

elif len(theParts) == 3 :  # Valid equation, compute it and prints its result.


    # For debug purposes - We can index a list just like a string using [index]
    print("\nThe equation entered by the user is %s %s %s." %(theParts[0], theParts[1], theParts[2]))


print("\nBye!")