Python converter: number-to-English - Project Euler 17

Question

So I wrote this function to convert a given number to its interpretation in the English language as part of the Project Euler exercises. It works fine, but I sense that it's rather sloppy and inelegant, especially for Python where many things can be done quickly in a couple of lines. Any feedback on how to make this code more beautiful/Pythonic is appreciated!

NUMBER_WORDS = {
 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",
 20 : "twenty",
 30 : "thirty",
 40 : "forty",
 50 : "fifty",
 60 : "sixty",
 70 : "seventy",
 80 : "eighty",
 90 : "ninety"
}
def convert_number_to_words(num):
 #Works up to 99,999
 num = str(num)
 analyze = 0
 postfix = remainder = None
 string = ""
 if len(num) > 4:
 analyze = int(num[0:2])
 remainder = num[2:]
 postfix = " thousand "
 elif len(num) > 3:
 analyze = int(num[0:1])
 remainder = num[1:]
 postfix = " thousand "
 elif len(num) > 2:
 analyze = int(num[0:1])
 remainder = num[1:]
 postfix = " hundred "
 if int(remainder) > 0:
 postfix += "and "
 elif int(num) in NUMBER_WORDS:
 analyze = int(num)
 else:
 analyze = int(num[0:1] + "0")
 remainder = num[1:]
 postfix = "-"
 string = NUMBER_WORDS[analyze]
 if postfix is not None:
 string += postfix
 if remainder is not None and int(remainder) > 0:
 return string + convert_number_to_words(remainder)
 else:
 return string

• TyCobb: "And" is normally reserved for writing out fractions. 13,500 would be "thirteen thousand and five hundred" in your example, but would be said as "thirteen thousand five hundred".
• asteri: @TyCobb Ah, good point. Editted. I'm with you that "and" shouldn't be included at all, but it's in the directions of the problem: projecteuler.net/problem=17

Answer 1

Here's one using modulo % and list joining that uses your original NUMBER_WORDS dict:

def int_to_english(n):
 english_parts = []
 ones = n % 10
 tens = n % 100
 hundreds = math.floor(n / 100) % 10
 thousands = math.floor(n / 1000)
 if thousands:
 english_parts.append(int_to_english(thousands))
 english_parts.append('thousand')
 if not hundreds and tens:
 english_parts.append('and')
 if hundreds:
 english_parts.append(NUMBER_WORDS[hundreds])
 english_parts.append('hundred')
 if tens:
 english_parts.append('and')
 if tens:
 if tens < 20 or ones == 0:
 english_parts.append(NUMBER_WORDS[tens])
 else:
 english_parts.append(NUMBER_WORDS[tens - ones])
 english_parts.append(NUMBER_WORDS[ones])
 return ' '.join(english_parts)

It works up to 999,999, but could be extended further with a little customisation.

• oliverpool: Your very last else shouldn't append 2 elements but insert them at once with a - as separation