Print an integer in English

english_num.py

"""Print a number."""

from __future__ import print_function


size_names = [
    "", "thousand", "million", "billion", "trillion", "quadrillion",
    "quintillion", "sexillion", "septillion", "nonillion", "decillion"
]
num_names = [
    "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
    "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen",
    "seventeen", "eighteen", "nineteen"
]
tens_names = [
    "", "", "twenty", "thirty", "fourty", "fifty", "sixty", "seventy", "eighty",
    "ninety"
]


def reverse(l):
    """Reverse iterable l."""
    return l[::-1]


def reverse_elems(l):
    """Reverse the iterable elements of an iterable l."""
    return [x[::-1] for x in l]


def pipe(val, *funcs):
    """Pipe a value through multiple functions."""
    for func in funcs:
        val = func(val)

    return val


def chunk(l, n=3):
    """Yield successive n-sized chunks from l."""
    for i in range(0, len(l), n):
        yield l[i:i + n]


def quantity(num):
    """Get string for a 3-digit number in English."""
    tens = 0
    segments = []

    if len(num) > 2:
        hundreds = int(num[-3])
        if hundreds > 0:
            segments.append("{} hundred".format(num_names[hundreds]))
    if len(num) > 1:
        tens = int(num[-2])
        if tens > 1:
            segments.append(tens_names[tens])
    if len(num) > 0:
        ones = int(num[-1])
        if tens != 1:
            # We don't want the tens place to affect this section unless it's 1
            tens = 0
        segments.append(num_names[tens * 10 + ones])

    return " ".join([x for x in segments if len(x) > 0])


def print_num(num):
    """Pretty print an integer in English."""
    sign = ""
    if num == 0:
        print("zero")
        return

    if num < 0:
        sign = "negative "
        num = -num

    segments = pipe(
        num,
        str,
        reverse,
        chunk,
        reverse_elems,
        enumerate,
        list,
        reverse
    )

    english_segments = [
        "{} {}".format(quantity(seg), size_names[x])
        for x, seg in segments
        if len(quantity(seg)) > 0
    ]

    print(sign + " ".join(english_segments))


def main():
    """Example driver."""
    print_num(int(input("Enter a number: ")))


if __name__ == "__main__":
    main()