# info > python yaml --- type: CommandReference command: python mode: man section: 1 source: man-pages --- ## Quick Reference - `python script.py` — run a script - `python -c 'print("hello")'` — execute a command - `python -m module_name` — run a module as a script - `python -i script.py` — run script then enter interactive mode - `python -O script.py` — run with basic optimizations (remove assert, __debug__) - `python -B script.py` — run without writing .pyc files - `python -W ignore::DeprecationWarning` — suppress deprecation warnings - `python -X dev script.py` — run with development mode (extra checks) ## Name python - an interpreted, interactive, object-oriented programming language ## Synopsis `python [ -B ] [ -b ] [ -d ] [ -E ] [ -h ] [ -i ] [ -I ] [ -m module-name ] [ -q ] [ -O ] [ -OO ] [ -s ] [ -S ] [ -u ] [ -v ] [ -V ] [ -W argument ] [ -x ] [ -X option ] [ -? ] [ --check-hash-based-pycs default | always | never ] [ -c command | script | - ] [ arguments ]` ## Description Python is an interpreted, interactive, object-oriented programming language. When called with standard input connected to a tty, it prompts for commands and executes them until EOF. When called with a file name argument or with a file as standard input, it reads and executes a script from that file. When called with `-c command`, it executes the Python statement(s) given as command. The script name and additional arguments are passed in `sys.argv` (a list of strings). In interactive mode, the primary prompt is `>>>` and the secondary prompt is `...`. The interpreter quits on EOF at a prompt. Unhandled exceptions print a stack trace; in non-interactive mode the interpreter exits. The interrupt signal raises `KeyboardInterrupt`. ## Options ### General - `-c command` — specify the command to execute; terminates option list - `-h`, `-?`, `--help` — print usage and exit - `-V`, `--version` — print Python version number and exit; twice for build info - `-m module-name` — run module as script; terminates option list - `-?` — same as `-h` ### Execution - `-i` — enter interactive mode after executing script or `-c` command; do not read `$PYTHONSTARTUP` - `-I` — isolated mode (implies `-E` and `-s`); ignores `PYTHON*` env vars, restricts `sys.path` - `-s` — don't add user site directory to `sys.path` - `-S` — disable import of the `site` module and site-dependent `sys.path` manipulations - `-u` — force stdout and stderr to be unbuffered (no effect on stdin) - `-x` — skip the first line of source (DOS hack); line numbers in errors will be off by one - `-q` — do not print version and copyright messages (also suppressed in non-interactive mode) ### Optimization and bytecode - `-O` — remove assert statements and `__debug__` conditionals; add `.opt-1` to `.pyc` filename - `-OO` — do `-O` and also discard docstrings; add `.opt-2` to `.pyc` filename - `-B` — don't write `.pyc` files on import (see also `PYTHONDONTWRITEBYTECODE`) - `--check-hash-based-pycs mode` — control how hash-based `.pyc` files are checked (`default`, `always`, `never`) ### Warning control - `-b` — issue warnings about `str(bytes_instance)`, `str(bytearray_instance)`, and comparing bytes/bytearray with str; `-bb` issues errors - `-W argument` — warning control. Argument can be: - `-Wdefault`, `-Werror`, `-Walways`, `-Wmodule`, `-Wonce`, `-Wignore` - Full form: `action:message:category:module:lineno` - Multiple `-W` options can be given; last matching action wins. Invalid `-W` options are ignored. ### Debugging and diagnostics - `-d` — parser debugging output (expert only, depends on compilation) - `-v` — print message each time a module is initialized; twice for file checks and module cleanup info - `-X option` — set implementation-specific option: - `-X faulthandler` — enable faulthandler - `-X showrefcount` — output total reference count and memory blocks (debug builds only) - `-X tracemalloc[=NFRAME]` — start tracing Python memory allocations - `-X importtime` — show how long each import takes - `-X dev` — enable CPython development mode (adds runtime checks, debug hooks, asyncio debug, etc.) - `-X utf8[=0]` — enable UTF-8 mode for OS interfaces; `-X utf8=0` disables - `-X pycache_prefix=PATH` — write `.pyc` files to a parallel tree - `-X warn_default_encoding` — enable `EncodingWarning` for `encoding=None` - `-X int_max_str_digits=number` — limit size of int<->str conversions (default: `sys.int_info.default_max_str_digits`) - `-E` — ignore environment variables `PYTHONPATH`, `PYTHONHOME`, etc. ## Environment Variables - `PYTHONHOME` — change location of standard Python libraries (default: `{prefix}/lib/python`) - `PYTHONPATH` — augment default search path for module files (colon-separated directories) - `PYTHONPLATLIBDIR` — override `sys.platlibdir` - `PYTHONSTARTUP` — execute commands from this file before first prompt in interactive mode - `PYTHONOPTIMIZE` — equivalent to `-O` (non-empty string) or `-O` multiple times (integer) - `PYTHONDEBUG` — equivalent to `-d` (non-empty string) or multiple `-d` (integer) - `PYTHONDONTWRITEBYTECODE` — equivalent to `-B` (non-empty string) - `PYTHONINSPECT` — equivalent to `-i` (non-empty string) - `PYTHONIOENCODING` — override encoding for stdin/stdout/stderr (format: `encoding:errorhandler`; stderr always uses `backslashreplace`) - `PYTHONNOUSERSITE` — equivalent to `-s` (non-empty string) - `PYTHONUNBUFFERED` — equivalent to `-u` (non-empty string) - `PYTHONVERBOSE` — equivalent to `-v` (non-empty string) or multiple `-v` (integer) - `PYTHONWARNINGS` — comma-separated string, equivalent to multiple `-W` options - `PYTHONHASHSEED` — set to `"random"` for random seed, or an integer in `[0, 4294967295]` for fixed seed (0 disables hash randomization) - `PYTHONINTMAXSTRDIGITS` — limit maximum digit characters in int<->str conversions (0 disables limit; bases 2,4,8,16,32 never limited) - `PYTHONMALLOC` — set memory allocator (`malloc`, `pymalloc`) and debug hooks (`debug`, `malloc_debug`, `pymalloc_debug`) - `PYTHONMALLOCSTATS` — print pymalloc statistics on arena creation and shutdown (ignored if `PYTHONMALLOC` forces C malloc or no pymalloc) - `PYTHONASYNCIODEBUG` — enable asyncio debug mode (non-empty string) - `PYTHONTRACEMALLOC` — start tracing memory allocations with tracemalloc; value is max frames in traceback - `PYTHONFAULTHANDLER` — call `faulthandler.enable()` at startup (equivalent to `-X faulthandler`) - `PYTHONEXECUTABLE` — override `sys.argv[0]` (Mac OS X only) - `PYTHONUSERBASE` — define user base directory for site-packages and Distutils install paths - `PYTHONPROFILEIMPORTTIME` — show import times (equivalent to `-X importtime`) - `PYTHONBREAKPOINT` — set to `0` to disable default debugger, or set to a callable **Debug-build only:** - `PYTHONTHREADDEBUG` — print threading debug info (deprecated in 3.10, removed in 3.12) - `PYTHONDUMPREFS` — dump objects and reference counts after shutdown ## Files and Directories - `${exec_prefix}/bin/python` — recommended location of the interpreter - `${prefix}/lib/python`, `${exec_prefix}/lib/python` — standard modules - `${prefix}/include/python`, `${exec_prefix}/include/python` — include files for developing extensions / embedding On Debian GNU/{Hurd,Linux}, default for both `${prefix}` and `${exec_prefix}` is `/usr`. ## See Also - `pydoc` — documentation viewer for Python modules and packages ## Internet Resources - Main website: - Documentation: - Developer resources: - Downloads: - Module repository: - Newsgroups: `comp.lang.python`, `comp.lang.python.announce` ## Licensing Python is distributed under an Open Source license. See the file "LICENSE" in the Python source distribution for terms and conditions and a disclaimer of all warranties.