booklet.py

#!/usr/bin/env python3.9
from itertools import chain
from typing import Iterator
import argh
ichain = chain.from_iterable

def up_to_multiple(mul: int, val: int) -> int:
    """
    Rounds a value up to the nearest multiple
    """
    return val + (0 if val % mul == 0 else (mul - val % mul))


def booklet(pages: int, filler_page: int = 0) -> Iterator[int]:
    """
    Returns a permutation representing the order of pages for a
    booklet style print
    """
    padded = up_to_multiple(4, pages)
    for page in ichain((padded - i, i + 1, i + 2, padded - (i + 1)) for i in range(0, padded//2, 2)):
        yield filler_page if page > pages else page

@argh.arg('pages', type=int, help='Number of pages')
# Argh! argh does not merge inferred parameters and given ones
#@argh.arg('filler_page', help='Filler number used for page numbers not multiple of 4')
#@argh.arg('separator', help='Separator between the permutation values')
def cmd_booklet(pages: int, filler_page: int = 0, separator: str = ','):
    """
    Computes the permutation representing the order of pages
    for a booklet style print
    """
    return separator.join(str(page) for page in booklet(pages, filler_page))

if __name__ == '__main__':
    argh.dispatch_command(cmd_booklet)