def check_args(parser, args):
<EOL>if len([a for a in [args.create, args.extract, args.verify, args.list,<EOL>args.list_detailed, args.hash, args.add_signature] if a<EOL>is not None]) != <NUM_LIT:1>:<EOL><INDENT>parser.error("<STR_LIT>")<EOL><DEDENT>if args.create and not args.files:<EOL><INDENT>parser.error("<STR_LIT>")<EOL><DEDENT>if args.extract and args.compression not in (None, '<STR_LIT>', '<STR_LIT>', '<STR_LIT>'):  <EOL><INDENT>parser.error('<STR_LIT>')<EOL><DEDENT>if args.create and args.compression not in (None, '<STR_LIT>', '<STR_LIT>'):  <EOL><INDENT>parser.error('<STR_LIT>')<EOL><DEDENT>if args.hash and len(args.files) != <NUM_LIT:1>:<EOL><INDENT>parser.error("<STR_LIT>")<EOL><DEDENT>
Validate commandline arguments.