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Inspired by the recent surge of questions dealing with changing numbers to their English equivalents (See here, here, and here), I decided to write my own version in Python.

Inspired by the recent surge of questions dealing with changing numbers to their English equivalents (See here, here, and here), I decided to write my own version in Python.

zero_to_nineteen = ("zero", "one", "two", "three", "four",
 "five", "six", "seven", "eight", "nine",
 "ten", "eleven", "twelve", "thirteen", "fourteen",
 "fifteen", "sixteen", "seventeen", "eighteen", "nineteen")
tens = ("zero", "ten", "twenty", "thirty", "forty",
 "fifty", "sixty", "seventy", "eighty", "ninety")
suffixes = {
 3 : "thousand",
 6 : "million",
 9 : "billion",
 12 : "trillion",
 15 : "quadrillion",
 18 : "quintillion",
 21 : "sextillion",
 24 : "septillion",
 27 : "octillion",
 30 : "nonillion",
 33 : "decillion",
 36 : "undecillion"
 39 : "duodecillion",
 42 : "tredicillion",
 45 : "quattuordecillion",
 48 : "quinquadecillion",
 51 : "sedecillion",
 54 : "septendecillion",
 57 : "octodecillion",
 60 : "novendecillion",
 63 : "vigintillion",
 66 : "unvigintillion",
 69 : "duovigintillion",
 72 : "tresvigintillion",
 75 : "quattuorvigintillion",
 78 : "quinquavigintillion",
 81 : "sesvigintillion",
 84 : "septemvigintillion",
 87 : "octovigintillion",
 90 : "novemvigintillion",
 93 : "trigintillion",
 96 : "untrigintillion",
 99 : "duotrigintillion",
 102 : "trestrigintilion",
 105 : "quattuortrigintillion",
 108 : "quinquatrigintillion",
 111 : "sestrigintillion",
 114 : "septentrigintillion",
 117 : "octotrigintillion",
 120 : "noventrigintillion",
 123 : "quadragintillion"
}
def spell_out(number):
 """Returns a string representation of the number, in english"""
 if isinstance(number, float):
 raise ValueError("number must be an integer")
 
 if number < 0:
 return "negative " + spell_out(-1 * number)
 
 if number < 20:
 return zero_to_nineteen[number]
 
 if number < 100:
 tens_digit = number // 10
 ones_digit = number % 10
 if ones_digit == 0:
 return tens[tens_digit]
 else:
 return "{}-{}".format(tens[tens_digit], zero_to_nineteen[ones_digit])
 
 if number < 1000:
 hundreds_digit = zero_to_nineteen[number // 100]
 rest = number % 100
 if rest == 0:
 return "{} hundred".format(hundreds_digit)
 else:
 return "{} hundred {}".format(hundreds_digit, spell_out(rest))
 
 suffix_index = log(number)
 suffix_index -= suffix_index % 3
 
 prefix = spell_out(number // 10 ** suffix_index)
 suffix = suffixes[suffix_index]
 
 rest_of_number = number % (10 ** suffix_index)
 
 if suffix_index in suffixes:
 if number % (10 ** suffix_index) == 0:
 return "{} {}".format(prefix, suffix)
 else:
 return "{} {} {}".format(prefix, suffix, spell_out(rest_of_number))
 
 return "infinity"
def log(number):
 """Returns integer which is log base 10 of number"""
 answer = 0
 while number > 9:
 answer += 1
 number //= 10
 return answer

I would appreciate any comments on my code.

Update: Changed formatting of zero_to_nineteen and tens as per @Davidmh's answer below.

zero_to_nineteen = ("zero", "one", "two", "three", "four",
 "five", "six", "seven", "eight", "nine",
 "ten", "eleven", "twelve", "thirteen", "fourteen",
 "fifteen", "sixteen", "seventeen", "eighteen", "nineteen")
tens = ("zero", "ten", "twenty", "thirty", "forty",
 "fifty", "sixty", "seventy", "eighty", "ninety")
suffixes = {
 3 : "thousand",
 6 : "million",
 9 : "billion",
 12 : "trillion",
 15 : "quadrillion",
 18 : "quintillion",
 21 : "sextillion",
 24 : "septillion",
 27 : "octillion",
 30 : "nonillion",
 33 : "decillion",
 36 : "undecillion"
 39 : "duodecillion",
 42 : "tredicillion",
 45 : "quattuordecillion",
 48 : "quinquadecillion",
 51 : "sedecillion",
 54 : "septendecillion",
 57 : "octodecillion",
 60 : "novendecillion",
 63 : "vigintillion",
 66 : "unvigintillion",
 69 : "duovigintillion",
 72 : "tresvigintillion",
 75 : "quattuorvigintillion",
 78 : "quinquavigintillion",
 81 : "sesvigintillion",
 84 : "septemvigintillion",
 87 : "octovigintillion",
 90 : "novemvigintillion",
 93 : "trigintillion",
 96 : "untrigintillion",
 99 : "duotrigintillion",
 102 : "trestrigintilion",
 105 : "quattuortrigintillion",
 108 : "quinquatrigintillion",
 111 : "sestrigintillion",
 114 : "septentrigintillion",
 117 : "octotrigintillion",
 120 : "noventrigintillion",
 123 : "quadragintillion"
}
def spell_out(number):
 """Returns a string representation of the number, in english"""
 if isinstance(number, float):
 raise ValueError("number must be an integer")
 
 if number < 0:
 return "negative " + spell_out(-1 * number)
 
 if number < 20:
 return zero_to_nineteen[number]
 
 if number < 100:
 tens_digit = number // 10
 ones_digit = number % 10
 if ones_digit == 0:
 return tens[tens_digit]
 else:
 return "{}-{}".format(tens[tens_digit], zero_to_nineteen[ones_digit])
 
 if number < 1000:
 hundreds_digit = zero_to_nineteen[number // 100]
 rest = number % 100
 if rest == 0:
 return "{} hundred".format(hundreds_digit)
 else:
 return "{} hundred {}".format(hundreds_digit, spell_out(rest))
 
 suffix_index = log(number)
 suffix_index -= suffix_index % 3
 
 prefix = spell_out(number // 10 ** suffix_index)
 suffix = suffixes[suffix_index]
 
 rest_of_number = number % (10 ** suffix_index)
 
 if suffix_index in suffixes:
 if number % (10 ** suffix_index) == 0:
 return "{} {}".format(prefix, suffix)
 else:
 return "{} {} {}".format(prefix, suffix, spell_out(rest_of_number))
 
 return "infinity"
def log(number):
 """Returns integer which is log base 10 of number"""
 answer = 0
 while number > 9:
 answer += 1
 number //= 10
 return answer

I would appreciate any comments on my code.

zero_to_nineteen = ("zero", "one", "two", "three", "four",
 "five", "six", "seven", "eight", "nine",
 "ten", "eleven", "twelve", "thirteen", "fourteen",
 "fifteen", "sixteen", "seventeen", "eighteen", "nineteen")
tens = ("zero", "ten", "twenty", "thirty", "forty",
 "fifty", "sixty", "seventy", "eighty", "ninety")
suffixes = {
 3 : "thousand",
 6 : "million",
 9 : "billion",
 12 : "trillion",
 15 : "quadrillion",
 18 : "quintillion",
 21 : "sextillion",
 24 : "septillion",
 27 : "octillion",
 30 : "nonillion",
 33 : "decillion",
 36 : "undecillion"
 39 : "duodecillion",
 42 : "tredicillion",
 45 : "quattuordecillion",
 48 : "quinquadecillion",
 51 : "sedecillion",
 54 : "septendecillion",
 57 : "octodecillion",
 60 : "novendecillion",
 63 : "vigintillion",
 66 : "unvigintillion",
 69 : "duovigintillion",
 72 : "tresvigintillion",
 75 : "quattuorvigintillion",
 78 : "quinquavigintillion",
 81 : "sesvigintillion",
 84 : "septemvigintillion",
 87 : "octovigintillion",
 90 : "novemvigintillion",
 93 : "trigintillion",
 96 : "untrigintillion",
 99 : "duotrigintillion",
 102 : "trestrigintilion",
 105 : "quattuortrigintillion",
 108 : "quinquatrigintillion",
 111 : "sestrigintillion",
 114 : "septentrigintillion",
 117 : "octotrigintillion",
 120 : "noventrigintillion",
 123 : "quadragintillion"
}
def spell_out(number):
 """Returns a string representation of the number, in english"""
 if isinstance(number, float):
 raise ValueError("number must be an integer")
 
 if number < 0:
 return "negative " + spell_out(-1 * number)
 
 if number < 20:
 return zero_to_nineteen[number]
 
 if number < 100:
 tens_digit = number // 10
 ones_digit = number % 10
 if ones_digit == 0:
 return tens[tens_digit]
 else:
 return "{}-{}".format(tens[tens_digit], zero_to_nineteen[ones_digit])
 
 if number < 1000:
 hundreds_digit = zero_to_nineteen[number // 100]
 rest = number % 100
 if rest == 0:
 return "{} hundred".format(hundreds_digit)
 else:
 return "{} hundred {}".format(hundreds_digit, spell_out(rest))
 
 suffix_index = log(number)
 suffix_index -= suffix_index % 3
 
 prefix = spell_out(number // 10 ** suffix_index)
 suffix = suffixes[suffix_index]
 
 rest_of_number = number % (10 ** suffix_index)
 
 if suffix_index in suffixes:
 if number % (10 ** suffix_index) == 0:
 return "{} {}".format(prefix, suffix)
 else:
 return "{} {} {}".format(prefix, suffix, spell_out(rest_of_number))
 
 return "infinity"
def log(number):
 """Returns integer which is log base 10 of number"""
 answer = 0
 while number > 9:
 answer += 1
 number //= 10
 return answer

I would appreciate any comments on my code.

zero_to_nineteen = ("zero", "one", "two", "three", "four",
 "five", "six", "seven", "eight", "nine",
 "ten", "eleven", "twelve", "thirteen", "fourteen",
 "fifteen", "sixteen", "seventeen", "eighteen", "nineteen")
tens = ("zero", "ten", "twenty", "thirty", "forty",
 "fifty", "sixty", "seventy", "eighty", "ninety")
suffixes = {
 3 : "thousand",
 6 : "million",
 9 : "billion",
 12 : "trillion",
 15 : "quadrillion",
 18 : "quintillion",
 21 : "sextillion",
 24 : "septillion",
 27 : "octillion",
 30 : "nonillion",
 33 : "decillion",
 36 : "undecillion"
 39 : "duodecillion",
 42 : "tredicillion",
 45 : "quattuordecillion",
 48 : "quinquadecillion",
 51 : "sedecillion",
 54 : "septendecillion",
 57 : "octodecillion",
 60 : "novendecillion",
 63 : "vigintillion",
 66 : "unvigintillion",
 69 : "duovigintillion",
 72 : "tresvigintillion",
 75 : "quattuorvigintillion",
 78 : "quinquavigintillion",
 81 : "sesvigintillion",
 84 : "septemvigintillion",
 87 : "octovigintillion",
 90 : "novemvigintillion",
 93 : "trigintillion",
 96 : "untrigintillion",
 99 : "duotrigintillion",
 102 : "trestrigintilion",
 105 : "quattuortrigintillion",
 108 : "quinquatrigintillion",
 111 : "sestrigintillion",
 114 : "septentrigintillion",
 117 : "octotrigintillion",
 120 : "noventrigintillion",
 123 : "quadragintillion"
}
def spell_out(number):
 """Returns a string representation of the number, in english"""
 if isinstance(number, float):
 raise ValueError("number must be an integer")
 
 if number < 0:
 return "negative " + spell_out(-1 * number)
 
 if number < 20:
 return zero_to_nineteen[number]
 
 if number < 100:
 tens_digit = number // 10
 ones_digit = number % 10
 if ones_digit == 0:
 return tens[tens_digit]
 else:
 return "{}-{}".format(tens[tens_digit], zero_to_nineteen[ones_digit])
 
 if number < 1000:
 hundreds_digit = zero_to_nineteen[number // 100]
 rest = number % 100
 if rest == 0:
 return "{} hundred".format(hundreds_digit)
 else:
 return "{} hundred {}".format(hundreds_digit, spell_out(rest))
 
 suffix_index = log(number)
 suffix_index -= suffix_index % 3
 
 prefix = spell_out(number // 10 ** suffix_index)
 suffix = suffixes[suffix_index]
 
 rest_of_number = number % (10 ** suffix_index)
 
 if suffix_index in suffixes:
 if number % (10 ** suffix_index) == 0:
 return "{} {}".format(prefix, suffix)
 else:
 return "{} {} {}".format(prefix, suffix, spell_out(rest_of_number))
 
 return "infinity"
def log(number):
 """Returns integer which is log base 10 of number"""
 answer = 0
 while number > 9:
 answer += 1
 number //= 10
 return answer

I would appreciate any comments on my code.

Update: Changed formatting of zero_to_nineteen and tens as per @Davidmh's answer below.