Bug report

Bug description:

When setting the default of an argument to sys.stdout and the type isargparse.FileType("wb") then the class should be_io.BufferedWriter not_io.TextIOWrapper when no arguments are provided. When the argument is set to- then the class is correctly set to_io.BufferedWriter as expected.

importargparseimportsysparser=argparse.ArgumentParser()parser.add_argument("outfile",nargs="?",type=argparse.FileType("wb"),default=sys.stdout)args=parser.parse_args("-")print(type(args.outfile))# <class '_io.BufferedWriter'># Correctargs=parser.parse_args()print(type(args.outfile))# <class '_io.TextIOWrapper'># Incorrect

CPython versions tested on:

3.14

Operating systems tested on:

Linux