XZise added a comment.
It is also using the regex if no module is installed so for Python 2 users there will be no difference.
And what John said: The module works almost exactly like the regex. The only difference is that it allows leading zeros in the IPv4 part of an IPv6 address. Those could be interpreted as octal numbers so it is disallowed to avoid ambiguity. And after that is fixed, the chance that Python 2 users will have it sooner is higher as they are using the backport (so all versions are fixed and it's not like 3.4.2 which will still have that problem).
TASK DETAIL https://phabricator.wikimedia.org/T76286
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To: jayvdb, XZise Cc: Multichill, gerritbot, jayvdb, Ricordisamoa, XZise, pywikipedia-bugs