def s3_keys_from_cmdline(opt):
    '''Retrieve S3 access keys from the command line, or None if not present.'''
    if opt.access_key != None and opt.secret_key != None:
      keys = (opt.access_key, opt.secret_key)
      debug("read S3 keys from commandline")
      return keys
    else:
      return None
Retrieve S3 access keys from the command line, or None if not present.