-u : force the stdout and stderr streams to be unbuffered;

usage: C:\Python37\python.exe [option] ... [-c cmd | -m mod | file | -] [arg] ...
Options and arguments (and corresponding environment variables):
-h     : print this help message and exit (also --help)
-u     : force the stdout and stderr streams to be unbuffered;
         this option has no effect on stdin; also PYTHONUNBUFFERED=x

PYTHONIOENCODING: Encoding[:errors] used for stdin/stdout/stderr.

Other environment variables:
PYTHONSTARTUP: file executed on interactive startup (no default)
PYTHONCASEOK : ignore case in 'import' statements (Windows).
PYTHONUTF8: if set to 1, enable the UTF-8 mode.
PYTHONIOENCODING: Encoding[:errors] used for stdin/stdout/stderr.
PYTHONFAULTHANDLER: dump the Python traceback on fatal errors.