def convert_to_numbers(input_string):
    alphabet = {" ": 0, "a": 1, "b": 2, "c": 3, "d": 4, "e": 5, "f": 6,
                "g": 7, "h": 8, "i": 9, "j": 10, "k": 11, "l": 12,
                "m": 13, "n": 14, "o": 15, "p": 16, "q": 17, "r": 18,
                "s": 19, "t": 20, "u": 21, "v": 22, "w": 23, "x": 24,
                "y": 25, "z": 26}
    input_string = list(input_string)
    number_list = []
    for letters in input_string:
        if letters not in "abcdefghijklmnopqrstuvwxyz ":
            return ("Error: only input spaces and lowercase letters")
            break

        number_list.append(alphabet[letters])
    return number_list


def convert_to_letters(input_array):
    numbers_to_letters_dict = {0: " ", 1: "a", 2: "b", 3: "c", 4: "d", 5: "e",
                               6: "f", 7: "g", 8: "h", 9: "i", 10: "j",
                               11: "k", 12: "l", 13: "m", 14: "n", 15: "o",
                               16: "p", 17: "q",  18: "r", 19: "s", 20: "t",
                               21: "u", 22: "v", 23: "w", 24: "x", 25: "y",
                               26: "z"}

    word_list = []
    word = ""

    for numbers in input_array:
        if numbers > 27 or numbers < 0:
            return "Only numbers 0-26"
            break
        word_list.append(numbers_to_letters_dict[numbers])
    return (word.join(word_list))
