collapse a list of IP addresses

ipcollapse.py

#!/usr/bin/python3
# reads a list of IP subnets in CIDR notation from stdin and collapses it

import sys
import ipaddress

subnets6 = []
subnets4 = []

input_list = sys.stdin.readlines()

# parse subnets
for net in input_list:
	try:
		n = ipaddress.ip_network(net.strip())
		if n.version == 4:
			subnets4.append(n)
		else:
			subnets6.append(n)
	except ValueError:
		pass

for subnets in [subnets6, subnets4]:
	# remove duplicates
	subnets = list(set(subnets))

	# sort
	subnets.sort()

	# remove smaller subnets of larger ones
	lensubnets = len(subnets)
	i = 0
	while i < lensubnets-1:
		j = i+1
		while j <= lensubnets-1:
			if subnets[i].overlaps(subnets[j]):
				subnets.remove(subnets[j])
				lensubnets -= 1
			else:
				break
		i += 1

	# collapse neighbors
	i = 0
	while i < lensubnets-1:
		j = i+1
		while j <= lensubnets-1:
			if subnets[i].prefixlen == subnets[j].prefixlen and subnets[i].supernet().overlaps(subnets[j]):
				subnets[i] = subnets[i].supernet()
				subnets.pop(j)
				lensubnets -= 1
				if i > 0:
					i -= 1
					j -= 1
			else:
				break
		i += 1

	for net in subnets:
		print(net.with_prefixlen)