Produce correctly ordered page numbers for smooth booklet printing

booklet

#!/usr/bin/env python
# Copyright: (c) 2018, Federico Ficarelli <federico.ficarelli@gmail.com>
# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)

import argparse

parser = argparse.ArgumentParser(description="""Produces page numbers in the correct order for smooth booklet printing.

The output from the booklet command can then be used as input to a printing
application (e.g.: Acrobat Reader) or pdftk to directly rearrange pages:

$ pdftk in.pdf cat $(booklet 10) output out.pdf

Please note that in case of an odd page count, an extra page is inserted as
the first one:

$ booklet 3
4 1 2 3

This workaround ensures that the first actual page is printed on the
right side of the first face. The safest way to handle an odd page count
is to manually add a blank page to the original document:

$ convert xc:none -page A4 blank.pdf
$ pdftk A=in.pdf B=blank.pdf cat A B output padded.pdf

""", formatter_class=argparse.RawTextHelpFormatter)
parser.add_argument('npages', metavar='N', type=int, help='total number of pages of source document')
parser.add_argument('--separator', metavar='STR', type=str, default=' ',
                    help='string separator to be used for numbers output (default: " ")')


def booklet_pages(n_pages):
    n_p = n_pages if n_pages % 2 == 0 else n_pages + 1
    n_faces = int(n_p / 2)
    for i_face in range(n_faces):
        if i_face % 2 == 0:
            i_page_right = i_face
            i_page_left = (n_p - 1) - i_page_right
        else:
            i_page_left = i_face
            i_page_right = (n_p - 1) - i_page_left
        yield i_page_left
        yield i_page_right

 
if __name__ == '__main__':
    args = parser.parse_args()
    numbers = booklet_pages(args.npages)
    print(args.separator.join(str(i + 1) for i in numbers))