Python Pre Receive hook for checking commit messages

pre-receive.py

#!/bin/python
import sys
import re
import subprocess


#Format: "oldref newref branch"
line = sys.stdin.read()
(base, commit, ref) = line.strip().split()
new_branch_push = re.match(r'[^1-9]+', base)
branch_deleted = re.match(r'[^1-9]+', commit)
contains_commit_msg = False
if not new_branch_push:
    revs = base + "..." + commit
    proc = subprocess.Popen(['git', 'rev-list','--oneline','--first-parent', revs], stdout=subprocess.PIPE)
    lines = proc.stdout.readlines()
    if lines:
        for line in lines:
            rev = str(line)
            match = re.search(r'TICKET-[0-9]{2,5}|#TICKET-[0-9]{2,5}|HOTFIX|FORCE', rev)
            if match is not None:
                contains_commit_msg = True
if contains_commit_msg or new_branch_push or branch_deleted:
    exit(0)
else:
    print "Commit does not contain the story associated with the commit in the format: TICKET-123 or #TICKET-123"
    exit(1)

What is python version required?

Learned so much from this little script, really appreciated.