python code kata

num_in_words.py

BELOW_TWENTY = {
  1: "one",
  2: "two",
  3: "three",
  4: "four",
  5: "five",
  6: "six",
  7: "seven",
  8: "eight",
  9: "nine",
  10: "ten",
  11: "eleven",
  12: "twelve",
  13: "thirteen",
  14: "fourteen",
  15: "fifteen",
  16: "sixteen",
  17: "seventeen",
  18: "eighteen",
  19: "nineteen"
}

TENS_DIGITS = {
  2: "twenty",
  3: "thirty",
  4: "fourty",
  5: "fifty",
  6: "sixty",
  7: "seventy",
  8: "eighty",
  9: "ninety"
}

def num_in_words(number):
  words = []

  if number < 20: return BELOW_TWENTY[number] 
  if number < 100: return TENS_DIGITS[number / 10] + " " + num_in_words(number % 10).rstrip()
  if number < 1000: return BELOW_TWENTY[number / 100] + " hundred and " + num_in_words(number % 100)
  if number < 1000000: return num_in_words(number / 1000) + " thousand " + num_in_words(number % 1000)
  if number < 1000000000: return num_in_words(number / 1000000) + " million " + num_in_words(number % 1000000)
  if number < 1000000000000: return num_in_words(number / 1000000000) + " billion " + num_in_words(number % 1000000000)


assert(num_in_words(1) == "one")
assert(num_in_words(2) == "two")
assert(num_in_words(9) == "nine")
assert(num_in_words(10) == "ten")
assert(num_in_words(13) == "thirteen")
assert(num_in_words(21) == "twenty one")
assert(num_in_words(99) == "ninety nine")
assert(num_in_words(101) == "one hundred and one")
assert(num_in_words(567) == "five hundred and sixty seven")
assert(num_in_words(5672) == "five thousand six hundred and seventy two")
assert(num_in_words(3935612) == "three million nine hundred and thirty five thousand six hundred and twelve")
assert(num_in_words(3935411612) == "three billion nine hundred and thirty five million four hundred and eleven thousand six hundred and twelve")


print "Mathematical!"