def METHOD_NAME(target, source, env):
  """ Action function for `POUpdate` builder """
  import SCons.Action
  from SCons.Tool.GettextCommon import _init_po_files
  for tgt in target:
    if tgt.rexists():
      action = SCons.Action.Action('$MSGMERGECOM', '$MSGMERGECOMSTR')
    else:
      action = _init_po_files
    status = action([tgt], source, env)
    if status : return status
  return 0