pre-revprop-change svn hook in python

pre-revprop-change.py

# pre-revprop-change.py:
#
# Performs the following:
#  - Makes sure that only the log message may be modified
#  - Makes sure that the action is either addition or modification, but not deletion
#  - Makes sure that an empty log message isn't entered
#
# usage: pre-revprop-change.py -t REPOS REV USERNAME PROPNAME ACTION
# N.B. The new value of the property is passed via standard input
# e.g. in pre-revprop-change.cmd (under Windows)
#
#   PATH=C:\Python26;C:\Python26\Scripts
#   python.exe {common_hooks_dir}\pre-revprop-change.py %1 %2 %3 %4 %5

import os
import sys
import getopt
try:
  my_getopt = getopt.gnu_getopt
except AttributeError:
  my_getopt = getopt.getopt

import re

import svn
import svn.fs
import svn.repos
import svn.core

def check_prop_name(prop):
  if prop != 'svn:log':
    sys.stderr.write("\nYou may only edit the log message of a revision.")
    return False
  return True

def check_action(action):
  if action == 'D':
    sys.stderr.write("\nYou may only add or modify the log message of a revision, but not delete the log message.")
    return False
  return True	

def check_log_message():
  msg = sys.stdin.read()
  if msg == None or msg.strip() == "":
    sys.stderr.write("\nYou have engaged in the obscene act of attempting to enter an empty log message.\n\nPlease make another attempt, preferably including the Jira issue number in the log message.")
    return False
  return True

def usage_and_exit(error_msg=None):
  import os.path
  stream = error_msg and sys.stderr or sys.stdout
  if error_msg:
    stream.write("ERROR: %s\n\n" % error_msg)
  stream.write("USAGE: %s REPOS REV USERNAME PROPNAME ACTION\n"
               % (os.path.basename(sys.argv[0])))
  sys.exit(error_msg and 1 or 0)

def main(ignored_pool, argv):
  repos_path = None
  revision = None
  username = None
  prop_name = None
  action = None

  try:
    opts, args = my_getopt(argv[1:], 't:h?', ["help"])
  except:
    usage_and_exit("problem processing arguments / options.")
  for opt, value in opts:
    if opt == '--help' or opt == '-h' or opt == '-?':
      usage_and_exit()
    elif opt == '-t':
      txn_name = value
    else:
      usage_and_exit("unknown option '%s'." % opt)

  if len(args) > 5:
    usage_and_exit("maximum of five arguments allowed.")

  repos_path = svn.core.svn_path_canonicalize(args[0])
  revision = args[1]
  username = args[2]
  prop_name = args[3]
  action = args[4]

  fs = svn.repos.svn_repos_fs(svn.repos.svn_repos_open(repos_path))

  if check_prop_name(prop_name) and check_action(action) and check_log_message():
    sys.exit(0)
  else:
    sys.exit(1)
  
if __name__ == '__main__':
  sys.exit(svn.core.run_app(main, sys.argv))