def get_float(prompt):
    print(prompt)
    while True:
        try:
            return float(input("> "))
        except ValueError:
            print("Please enter a number")

done = False

while not done:

    while True:
        print("Would you like to convert from C TO F, or F TO C?")
        convert = input("> ").lower()
        if convert in ("c to f", "f to c"):
            break
        print("Please enter a valid command.")

    while True:
        if convert == "c to f":
            val = get_float("What temperature would you like to convert to Fahrenheit?")
            print("That's %.1f degrees Fahrenheit.\n" % (val * 9 / 5 + 32))
        else:
            val = get_float("What temperature would you like to convert to Celsius?")
            print("That's %.1f degrees Celsius.\n" % ((val - 32) * 5 / 9))

        print("Is that all? (Y/N)")
        if input("> ").lower() == "y":
            print("Goodbye")
            done = True
            break
        else:
            print("")