calculator.py

#help_screen
#Displays information about how the program works
# Accepts no parameters
# Returns nothing

def help_screen():
	print("Add: Adds two numbers")
	print("Subtract: Subtracts two numbers")
	print("Print: Displays the result of the latest operation")
	print("Help: Displays this help screen")
	print("Quit: Exits the program")

# menu
# Display a menu
# Accepts no parameters
# Returns the string entered by the user.

def menu():
	# Display a menu
	return input("=== A)dd S)ubtract P)rint H)elp Q)uit ===")


# main
# Runs a command loop that allows users to
# perform simple arithmetic.

def main():
	result = 0.0
	done  = False; # Initially not done
	while not done:
		choice = menu() # Get User choice

		if choice == "A" or choice == "a": # Addition
			arg1 = float(input("Enter arg 1:"))
			arg2 = float(input("Enter arg 2:"))
			result = arg1 + arg2
			print(result)
		elif choice == "S" or choice == "s": # Subtraction
			arg1 = float(input("Enter arg 1:"))
			arg2 = float(input("Enter arg 2:"))
			result = arg1 - arg2
			print(result)
		elif choice == "P" or choice == "p": #Print
			print(result)
		elif choice == "H" or choice == "h": #Help
			help_screen()
		elif choice == "Q" or choice == "q":#Quit
			done = True
main()