def num_to_char(value):
    if value == 2: return ["a","b","c"]
    if value == 3: return ["d","e","f"]
    if value == 4: return ["g","h","i"]
    if value == 5: return ["j","k","l"]
    if value == 6: return ["m","n","o"]
    if value == 7: return ["p","q","r","s"]
    if value == 8: return ["t","u","v"]
    if value == 9: return ["w","x","y","z"]

def convert_num(number, current_string = ""):
    if number == []:
        print(current_string)
        return
    get_list = num_to_char(int(number[0]))
    for character in get_list:
        current_string += character
        if len(number) >= 1:
            convert_num(number[1:], current_string)
            current_string = current_string[:-1]

num_to_covert = list("23")
convert_num(num_to_covert)