Subtracts one list of address ranges from another list of ranges, returning a list of addresses as /32 ranges.

subtract.py

#!/usr/bin/env python

# This program requires two filename arguments. Each file should contain a list
# of address ranges (CIDR blocks). The output will be a list of address which
# are in the first list but not the second expressed as /32 ranges.

from __future__ import unicode_literals

import sys
import ipaddress
import os

if __name__ == "__main__":
    assert len(sys.argv) == 3, "two arguments required"
    assert os.path.isfile(sys.argv[1]), "file %s does not exist" % sys.argv[1]
    assert os.path.isfile(sys.argv[2]), "file %s does not exist" % sys.argv[2]

    xs = {}

    f1 = open(sys.argv[1], 'r')
    for line in f1.readlines() :
        for x in ipaddress.IPv4Network(unicode(line.strip()), strict=False):
            xs[x] = True
    f1.close()

    f2 = open(sys.argv[2], 'r')
    for line in f2.readlines() :
        for x in ipaddress.IPv4Network(unicode(line.strip()), strict=False):
            if xs.get(x):
                del xs[x]
    f2.close()

    for x in xs:
        print "%s/32" % x