Prepare page numbers to print a booklet using n-up option in print dialog

booklet.py

#!/usr/bin/python3

import sys

# 4 ->  odd  -> 4,1
#       even -> 2,3

# 8 ->  odd  -> 8,1  6,3
#       even -> 2,7  4,5

# 12 -> odd  -> 12,1  10,3  8,5
#       even -> 2,11  4,9   6,7

# 16 -> odd  -> 16,1  14,3  12,5  10,7 
#       even -> 2,15  4,13  6,11  8,9

def booklet(pages):
    def ceil4(n):
        return n + (3 - ((n - 1) % 4))

    def fix(n, pages):
        return max(1, min(n, pages))

    odd = []
    even = []

    front, back = 1, ceil4(pages)
    for _ in range(0, ceil4(pages)//4):
        odd.append((fix(back, pages), fix(front, pages)))
        even.append((fix(front+1, pages), fix(back-1, pages)))
        front += 2
        back -= 2

    return (odd, even)

def format_pages(pages):
    return ",".join([f"\033[1m{l},{r}\033[0m" if i % 2 == 0 else f"{l},{r}\033[0m" for i, (l, r) in enumerate(pages)])

if len(sys.argv) < 2:
    print(f"usage: {sys.argv[0]} NUMBER-OF-PAGES", file=sys.stderr)
    exit(1)

pages = int(sys.argv[1])

odd, even = booklet(pages)

print("Odd:", format_pages(odd))
print("   ↺", format_pages(reversed(odd)))
print("Even:", format_pages(even))
print("    ↺", format_pages(reversed(even)))