# Tutorial 3 - Problem 5
#
# Write a function called eval_loop( ) that iteratively prompts the user,
# takes the resulting input and evaluates it using eval( ), and prints the result.
# It should continue until the user enters "done", and then return the value of the
# last expression it evaluated.
#
# Let's only consider equations of the form: operand> <operator> <operand>
# 
# Anne Lavergne
# Dec. 2015


def eval_loop( ):
  result = 0
  done = False
  while not done:
     equation = input("Please, enter an equation (format: <operand> <operator> <operand>): ")
     if len(equation) == 0:
       print("You have not entered anything! Try again!")
     else:
       if equation.isalpha( ):
         print("Have you entered '{}'? Try again!". format(equation))
       else:
         equationList = equation.split( )
         if 1 <= len(equationList) < 3:
           print("Have you entered a complete equation? Try again!")
         else :
           result = eval(equation)
           print(equation + " = %f" %result)
           userReply = input("If you wish to stop, please, enter 'done' otherwise press any key: ")
           if userReply.lower() == 'done' :
              done = True
  return result


# Main part of program
theResult = eval_loop( )

# Actual results:
##Please, enter an equation (format: <operand> <operator> <operand>): 
##You have not entered anything! Try again!
##Please, enter an equation (format: <operand> <operator> <operand>): Banana
##Have you entered 'Banana'? Try again!
##Please, enter an equation (format: <operand> <operator> <operand>): 2 4
##Have you entered a complete equation? Try again!
##Please, enter an equation (format: <operand> <operator> <operand>): 2 + 4
##2 + 4 = 6.000000
##If you wish to stop, please, enter 'done' otherwise press any key: done