Script to check the formal validity of a given ISBN-10 or ISBN-13.

checkisbn.py

#! /usr/bin/env python

import sys
import re

def is_valid(isbn):
	sum = 0
	isbn = re.sub(r"[-–—\s]", "", isbn)
	# in case of isbn13
	if len(isbn) == 13 and isbn[0:3] == "978" or "979":  # is it a ISBN? Thanks @librarythingtim
		for d, i in enumerate(isbn):
			if (int(d) + 1) % 2 != 0:
				sum += int(i)
			else:
				sum += int(i) * 3
		if sum % 10 == 0:
			return True
		else:
			return False
	# in case of isbn10
	elif len(isbn) == 10:
		isbn = list(isbn)
		if isbn[-1] == "X" or isbn[-1] == "x": #  a final x stands for 10
			isbn[-1] = 10
		for d, i in enumerate(isbn[:-1]):
			sum += (int(d)+1) * int(i)
		if (sum % 11) == int(isbn[-1]):
			return True
		else:
			return False
	else:
		return False

if __name__ == "__main__":
	if is_valid(sys.argv[1]):
		print sys.argv[1], "\t", "is a valid ISBN"
	else:
		print sys.argv[1], "\t", "is NOT a valid ISBN"