I'm currently converting a whole lot of IP address data from some quite ghastly flat files.Ghastliness aside, I'm trying to sort out a way to check each IP listed to check if it's a subnet address ...

Python 3.3 standard library 'ipaddress' suffers from a critical IP address vulnerability (CVE-2021-29921) identical to the flaw that was reported in the "netmask" library earlier this year.