Textualise an integer to natural English language in Python

textualise_number.py

def slice_number(num, skip_places, num_places):
    num //= 10**skip_places
    return num - ((num // 10**num_places) * 10**num_places)

def textualise_number(num):
    number_text = {
        0: 'zero',
        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',
        15: 'fifteen',
    }

    special_tens = {
        20: 'twenty',
        30: 'thirty',
        50: 'fifty',
    }

    if num < 100:
        out = []
        lsd = slice_number(num, 0, 1)
        second_lsd = slice_number(num, 1, 1)
        ten = second_lsd * 10

        if num in number_text:
            return number_text[num]

        if 10 < num < 20:
            return number_text[lsd].rstrip('t') + 'teen'

        if ten in special_tens:
            out.append(special_tens[ten])
        elif second_lsd > 0:
            out.append(number_text[second_lsd].rstrip('t') + 'ty')

        out.append(number_text[lsd])
        return ' '.join(out)

    out = []
    slices = [
        (0, 2, ''),
        (2, 1, 'hundred'),
        (3, 3, 'thousand'),
        (6, 3, 'million'),
        (9, 3, 'billion'),
        (12, 3, 'trillion'),
        (15, 3, 'quadrillion'),
    ]

    for skip_places, num_places, suffix in slices:
        if 10**skip_places > num:
            continue

        sliced = slice_number(num, skip_places, num_places)

        if sliced == 0:
            continue

        textualised = textualise_number(sliced)

        if not suffix:
            out.insert(0, 'and ' + textualised)
            continue

        out.insert(0, textualised + ' ' + suffix)

    return ' '.join(out)