https://qiita.com/hanakayui0628/items/f60ff2759b3e05a21c81

number2word.py

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', 100: 'Hundred',
         1000: 'Thousand', 1000000: 'Million', 1000000000: 'Billion'}
units = sorted(words, reverse=True)

def number2word(number):
    if number == 0:
        return 'Zero'
    def convert(number):
        if number < 0:
            yield 'Negative'
            number *= -1
        for unit in units:
            if number >= unit:
                if unit >= 100:
                    yield number2word(number // unit) + ' ' + words[unit]
                    number %= unit
                else:
                    yield words[unit]
                    number -= unit
    return ' '.join(convert(number))