-u -v -W arg -x -X 7 1.1. Command line Python Setup and Usage, Release 3.9.5 Force the stdout and stderr streams to be unbuffered. This option has no effect on the stdin stream. See also$_{PYTHONUNBUFFERED}$ . Changed in version 3.7: The text layer of the stdout and stderr streams now is unbuffered. Print a message each time a module is initialized, showing the place (filename or built-in module) from which it is loaded. When given twice ( -vv ), print a message for each file that is checked for when searching for a module. Also provides information on module cleanup at exit. See also PYTHONVERBOSE . Warning control. Python’s warning machinery by default prints warning messages to$_{sys.stderr}$ . A typical warning message has the following form: file:line: category: message Multiple $_{-W}$options may be given; when a warning matches more than one option, the action for the last matching option is performed. Invalid -W options are ignored (though, a warning message is printed about invalid options when the first warning is issued). By default, each warning is printed once for each source line where it occurs. This option controls how often warnings are printed. Warnings can also be controlled using the$_{PYTHONWARNINGS}$ environment variable and from within a Python program using the$_{warnings}$module. The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default): -Wdefault # Warn once per call location -Werror # Convert to exceptions -Walways # Warn every time -Wmodule # Warn once per calling module -Wonce # Warn once per Python process -Wignore # Never warn The action names can be abbreviated as desired (e.g. $_{-Wi}$,$_{-Wd}$ ,$_{-Wa}$ ,$_{-We}$) and the interpreter will resolve them to the appropriate action name. See warning-filter and describing-warning-filters for more details. Skip the first line of the source, allowing use of non-Unix forms of$_{#!cmd}$ . This is intended for a DOS specific hack only. • $_{-X importtime}$to show how long each import takes. It shows module name, cumulative time (includ- ing nested imports) and self time (excluding nested imports). Note that its output may be broken in multi- threaded application. Typical usage is python3 -X importtime -c 'import asyncio' . See also$_{PYTHONPROFILEIMPORTTIME}$ . • -X tracemalloc to start tracing Python memory allocations using the tracemalloc mod- ule. By default, only the most recent frame is stored in a traceback of a trace. Use -X $_{tracemalloc=NFRAME}$to start tracing with a traceback limit of NFRAME frames. See the tracemalloc.start() for more information. • -X showrefcount to output the total reference count and number of used memory blocks when the program finishes or after each statement in the interactive interpreter. This only works on debug builds. • -X oldparser : enable the traditional LL(1) parser. See also$_{PYTHONOLDPARSER}$ and PEP 617 . • -X faulthandler to enable$_{faulthandler}$ ; Reserved for various implementation-specific options. CPython currently defines the following possible values: