1.1.1.Interface options¶

The interpreter interface resembles that of the UNIX shell, but provides someadditional methods of invocation:

• When called with standard input connected to a tty device, it prompts forcommands and executes them until an EOF (an end-of-file character, you canproduce that withCtrl-D on UNIX orCtrl-Z,Enter on Windows) is read.For more on interactive mode, seeInteractive Mode.

• When called with a file name argument or with a file as standard input, itreads and executes a script from that file.

• When called with a directory name argument, it reads and executes anappropriately named script from that directory.

• When called with-ccommand, it executes the Python statement(s) given ascommand. Herecommand may contain multiple statements separated bynewlines. Leading whitespace is significant in Python statements!

• When called with-mmodule-name, the given module is located on thePython module path and executed as a script.

In non-interactive mode, the entire input is parsed before it is executed.

An interface option terminates the list of options consumed by the interpreter,all consecutive arguments will end up insys.argv – note that the firstelement, subscript zero (sys.argv[0]), is a string reflecting the program’ssource.

-c<command>¶

Execute the Python code incommand.command can be one or morestatements separated by newlines, with significant leading whitespace as innormal module code.

If this option is given, the first element ofsys.argv will be"-c" and the current directory will be added to the start ofsys.path (allowing modules in that directory to be imported as toplevel modules).

Raises anauditing eventcpython.run_command with argumentcommand.

Changed in version 3.14:command is automatically dedented before execution.

-m<module-name>¶

Searchsys.path for the named module and execute its contents asthe__main__ module.

Since the argument is amodule name, you must not give a file extension(.py). The module name should be a valid absolute Python module name, butthe implementation may not always enforce this (e.g. it may allow you touse a name that includes a hyphen).

Package names (including namespace packages) are also permitted. When apackage name is supplied insteadof a normal module, the interpreter will execute<pkg>.__main__ asthe main module. This behaviour is deliberately similar to the handlingof directories and zipfiles that are passed to the interpreter as thescript argument.

Note

This option cannot be used with built-in modules and extension moduleswritten in C, since they do not have Python module files. However, itcan still be used for precompiled modules, even if the original sourcefile is not available.

If this option is given, the first element ofsys.argv will be thefull path to the module file (while the module file is being located, thefirst element will be set to"-m"). As with the-c option,the current directory will be added to the start ofsys.path.

-I option can be used to run the script in isolated mode wheresys.path contains neither the current directory nor the user’ssite-packages directory. AllPYTHON* environment variables areignored, too.

Many standard library modules contain code that is invoked on their executionas a script. An example is thetimeit module:

python-mtimeit-s"setup here""benchmarked code here"python-mtimeit-h# for details

Raises anauditing eventcpython.run_module with argumentmodule-name.

See also

runpy.run_module()

Equivalent functionality directly available to Python code

PEP 338 – Executing modules as scripts

Changed in version 3.1:Supply the package name to run a__main__ submodule.

Changed in version 3.4:namespace packages are also supported

-

Read commands from standard input (sys.stdin). If standard input isa terminal,-i is implied.

If this option is given, the first element ofsys.argv will be"-" and the current directory will be added to the start ofsys.path.

Raises anauditing eventcpython.run_stdin with no arguments.

<script>

Execute the Python code contained inscript, which must be a filesystempath (absolute or relative) referring to either a Python file, a directorycontaining a__main__.py file, or a zipfile containing a__main__.py file.

If this option is given, the first element ofsys.argv will be thescript name as given on the command line.

If the script name refers directly to a Python file, the directorycontaining that file is added to the start ofsys.path, and thefile is executed as the__main__ module.

If the script name refers to a directory or zipfile, the script name isadded to the start ofsys.path and the__main__.py file inthat location is executed as the__main__ module.

-I option can be used to run the script in isolated mode wheresys.path contains neither the script’s directory nor the user’ssite-packages directory. AllPYTHON* environment variables areignored, too.

Raises anauditing eventcpython.run_file with argumentfilename.

See also

runpy.run_path()

Equivalent functionality directly available to Python code

If no interface option is given,-i is implied,sys.argv[0] isan empty string ("") and the current directory will be added to thestart ofsys.path. Also, tab-completion and history editing isautomatically enabled, if available on your platform (seeReadline configuration).

1.1.2.Generic options¶

-?¶

-h¶

--help¶

Print a short description of all command line options and correspondingenvironment variables and exit.

--help-env¶

Print a short description of Python-specific environment variablesand exit.

Added in version 3.11.

--help-xoptions¶

Print a description of implementation-specific-X optionsand exit.

Added in version 3.11.

--help-all¶

Print complete usage information and exit.

Added in version 3.11.

-V¶

--version¶

Print the Python version number and exit. Example output could be:

Python 3.8.0b2+

When given twice, print more information about the build, like:

Python 3.8.0b2+ (3.8:0c076caaa8, Apr 20 2019, 21:55:00)[GCC 6.2.0 20161005]

Added in version 3.6:The-VV option.

1.1.3.Miscellaneous options¶

-b¶

Issue a warning when convertingbytes orbytearray tostr without specifying encoding or comparingbytes orbytearray withstr orbytes withint.Issue an error when the option is given twice (-bb).

Changed in version 3.5:Affects also comparisons ofbytes withint.

-B¶

If given, Python won’t try to write.pyc files on theimport of source modules. See alsoPYTHONDONTWRITEBYTECODE.

--check-hash-based-pycsdefault|always|never¶

Control the validation behavior of hash-based.pyc files. SeeCached bytecode invalidation. When set todefault, checked and uncheckedhash-based bytecode cache files are validated according to their defaultsemantics. When set toalways, all hash-based.pyc files, whetherchecked or unchecked, are validated against their corresponding sourcefile. When set tonever, hash-based.pyc files are not validatedagainst their corresponding source files.

The semantics of timestamp-based.pyc files are unaffected by thisoption.

-d¶

Turn on parser debugging output (for expert only).See also thePYTHONDEBUG environment variable.

This option requires adebug build of Python, otherwiseit’s ignored.

-E¶

Ignore allPYTHON* environment variables, e.g.PYTHONPATH andPYTHONHOME, that might be set.

See also the-P and-I (isolated) options.

-i¶

Enter interactive mode after execution.

Using the-i option will enter interactive mode in any of the following circumstances:

• When a script is passed as first argument

• When the-c option is used

• When the-m option is used

Interactive mode will start even whensys.stdin does not appear to be a terminal. ThePYTHONSTARTUP file is not read.

This can be useful to inspect global variables or a stack trace when a scriptraises an exception. See alsoPYTHONINSPECT.

-I¶

Run Python in isolated mode. This also implies-E,-Pand-s options.

In isolated modesys.path contains neither the script’s directory northe user’s site-packages directory. AllPYTHON* environmentvariables are ignored, too. Further restrictions may be imposed to preventthe user from injecting malicious code.

Added in version 3.4.

-O¶

Remove assert statements and any code conditional on the value of__debug__. Augment the filename for compiled(bytecode) files by adding.opt-1 before the.pycextension (seePEP 488). See alsoPYTHONOPTIMIZE.

Changed in version 3.5:Modify.pyc filenames according toPEP 488.

-OO¶

Do-O and also discard docstrings. Augment the filenamefor compiled (bytecode) files by adding.opt-2 before the.pyc extension (seePEP 488).

Changed in version 3.5:Modify.pyc filenames according toPEP 488.

-P¶

Don’t prepend a potentially unsafe path tosys.path:

• python-mmodule command line: Don’t prepend the current workingdirectory.

• pythonscript.py command line: Don’t prepend the script’s directory.If it’s a symbolic link, resolve symbolic links.

• python-ccode andpython (REPL) command lines: Don’t prepend anempty string, which means the current working directory.

See also thePYTHONSAFEPATH environment variable, and-Eand-I (isolated) options.

Added in version 3.11.

-q¶

Don’t display the copyright and version messages even in interactive mode.

Added in version 3.2.

-R¶

Turn on hash randomization. This option only has an effect if thePYTHONHASHSEED environment variable is set to anything otherthanrandom, since hash randomization is enabled by default.

On previous versions of Python, this option turns on hash randomization,so that the__hash__() values of str and bytes objectsare “salted” with an unpredictable random value. Although they remainconstant within an individual Python process, they are not predictablebetween repeated invocations of Python.

Hash randomization is intended to provide protection against adenial-of-service caused by carefully chosen inputs that exploit the worstcase performance of a dict construction,O(n²) complexity. Seehttp://ocert.org/advisories/ocert-2011-003.html for details.

PYTHONHASHSEED allows you to set a fixed value for the hashseed secret.

Added in version 3.2.3.

Changed in version 3.7:The option is no longer ignored.

-s¶

Don’t add theusersite-packagesdirectory tosys.path.

See alsoPYTHONNOUSERSITE.

See also

PEP 370 – Per user site-packages directory

-S¶

Disable the import of the modulesite and the site-dependentmanipulations ofsys.path that it entails. Also disable thesemanipulations ifsite is explicitly imported later (callsite.main() if you want them to be triggered).

-u¶

Force the stdout and stderr streams to be unbuffered. This option has noeffect on the stdin stream.

See alsoPYTHONUNBUFFERED.

Changed in version 3.7:The text layer of the stdout and stderr streams now is unbuffered.

-v¶

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 whensearching for a module. Also provides information on module cleanup at exit.

Changed in version 3.10:Thesite module reports the site-specific pathsand.pth files being processed.

See alsoPYTHONVERBOSE.

-Warg¶

Warning control. Python’s warning machinery by default prints warningmessages tosys.stderr.

The simplest settings apply a particular action unconditionally to allwarnings emitted by a process (even those that are otherwise ignored bydefault):

-Wdefault# Warn once per call location-Werror# Convert to exceptions-Walways# Warn every time-Wall# Same as -Walways-Wmodule# Warn once per calling module-Wonce# Warn once per Python process-Wignore# Never warn

The action names can be abbreviated as desired and the interpreter willresolve them to the appropriate action name. For example,-Wi is thesame as-Wignore.

The full form of argument is:

action:message:category:module:lineno

Empty fields match all values; trailing empty fields may be omitted. Forexample-Wignore::DeprecationWarning ignores all DeprecationWarningwarnings.

Theaction field is as explained above but only applies to warnings thatmatch the remaining fields.

Themessage field must match the whole warning message; this match iscase-insensitive.

Thecategory field matches the warning category(ex:DeprecationWarning). This must be a class name; the match testwhether the actual warning category of the message is a subclass of thespecified warning category.

Themodule field matches the (fully qualified) module name; this match iscase-sensitive.

Thelineno field matches the line number, where zero matches all linenumbers and is thus equivalent to an omitted line number.

Multiple-W options can be given; when a warning matches more thanone option, the action for the last matching option is performed. Invalid-W options are ignored (though, a warning message is printed aboutinvalid options when the first warning is issued).

Warnings can also be controlled using thePYTHONWARNINGSenvironment variable and from within a Python program using thewarnings module. For example, thewarnings.filterwarnings()function can be used to use a regular expression on the warning message.

SeeThe Warnings Filter andDescribing Warning Filters for moredetails.

-x¶

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¶

Reserved for various implementation-specific options. CPython currentlydefines the following possible values:

• -Xfaulthandler to enablefaulthandler.See alsoPYTHONFAULTHANDLER.

  Added in version 3.3.

• -Xshowrefcount to output the total reference count and number of usedmemory blocks when the program finishes or after each statement in theinteractive interpreter. This only works ondebug builds.

  Added in version 3.4.

• -Xtracemalloc to start tracing Python memory allocations using thetracemalloc module. By default, only the most recent frame isstored in a traceback of a trace. Use-Xtracemalloc=NFRAME to starttracing with a traceback limit ofNFRAME frames.Seetracemalloc.start() andPYTHONTRACEMALLOCfor more information.

  Added in version 3.4.

• -Xint_max_str_digits configures theinteger string conversionlength limitation. See alsoPYTHONINTMAXSTRDIGITS.

  Added in version 3.11.

• -Ximporttime to show how long each import takes. It shows modulename, cumulative time (including nested imports) and self time (excludingnested imports). Note that its output may be broken in multi-threadedapplication. Typical usage ispython-Ximporttime-c'importasyncio'.

  -Ximporttime=2 enables additional output that indicates when animported module has already been loaded. In such cases, the stringcached will be printed in both time columns.

  See alsoPYTHONPROFILEIMPORTTIME.

  Added in version 3.7.

  Changed in version 3.14:Added-Ximporttime=2 to also trace imports of loaded modules,and reserved values other than1 and2 for future use.

• -Xdev: enablePython Development Mode, introducingadditional runtime checks that are too expensive to be enabled bydefault. See alsoPYTHONDEVMODE.

  Added in version 3.7.

• -Xutf8 enables thePython UTF-8 Mode.-Xutf8=0 explicitly disablesPython UTF-8 Mode(even when it would otherwise activate automatically).See alsoPYTHONUTF8.

  Added in version 3.7.

• -Xpycache_prefix=PATH enables writing.pyc files to a paralleltree rooted at the given directory instead of to the code tree. See alsoPYTHONPYCACHEPREFIX.

  Added in version 3.8.

• -Xwarn_default_encoding issues aEncodingWarning when thelocale-specific default encoding is used for opening files.See alsoPYTHONWARNDEFAULTENCODING.

  Added in version 3.10.

• -Xno_debug_ranges disables the inclusion of the tables mapping extralocation information (end line, start column offset and end column offset)to every instruction in code objects. This is useful when smaller codeobjects and pyc files are desired as well as suppressing the extra visuallocation indicators when the interpreter displays tracebacks. See alsoPYTHONNODEBUGRANGES.

  Added in version 3.11.

• -Xfrozen_modules determines whether or not frozen modules areignored by the import machinery. A value ofon means they getimported andoff means they are ignored. The default isonif this is an installed Python (the normal case). If it’s underdevelopment (running from the source tree) then the default isoff.Note that theimportlib_bootstrap andimportlib_bootstrap_external frozen modules are always used, evenif this flag is set tooff. See alsoPYTHON_FROZEN_MODULES.

  Added in version 3.11.

• -Xperf enables support for the Linuxperf profiler.When this option is provided, theperf profiler will be able toreport Python calls. This option is only available on some platforms andwill do nothing if is not supported on the current system. The default valueis “off”. See alsoPYTHONPERFSUPPORT andPython support for the Linux perf profiler.

  Added in version 3.12.

• -Xperf_jit enables support for the Linuxperf profiler with DWARFsupport. When this option is provided, theperf profiler will be ableto report Python calls using DWARF information. This option is only available onsome platforms and will do nothing if is not supported on the currentsystem. The default value is “off”. See alsoPYTHON_PERF_JIT_SUPPORTandPython support for the Linux perf profiler.

  Added in version 3.13.

• -Xdisable_remote_debug disables the remote debugging support as describedinPEP 768. This includes both the functionality to schedule code forexecution in another process and the functionality to receive code forexecution in the current process.

  This option is only available on some platforms and will do nothingif is not supported on the current system. See alsoPYTHON_DISABLE_REMOTE_DEBUG andPEP 768.

  Added in version 3.14.

• -Xcpu_count=n overridesos.cpu_count(),os.process_cpu_count(), andmultiprocessing.cpu_count().n must be greater than or equal to 1.This option may be useful for users who need to limit CPU resources of acontainer system. See alsoPYTHON_CPU_COUNT.Ifn isdefault, nothing is overridden.

  Added in version 3.13.

• -Xpresite=package.module specifies a module that should beimported before thesite module is executed and before the__main__ module exists. Therefore, the imported module isn’t__main__. This can be used to execute code early during Pythoninitialization. Python needs to bebuilt in debug modefor this option to exist. See alsoPYTHON_PRESITE.

  Added in version 3.13.

• -Xgil=0,1 forces the GIL to be disabled or enabled,respectively. Setting to0 is only available in builds configured with--disable-gil. See alsoPYTHON_GIL andFree-threaded CPython.

  Added in version 3.13.

• -Xthread_inherit_context=0,1 causesThreadto, by default, use a copy of context of the caller ofThread.start() when starting. Otherwise, threads will startwith an empty context. If unset, the value of this option defaultsto1 on free-threaded builds and to0 otherwise. See alsoPYTHON_THREAD_INHERIT_CONTEXT.

  Added in version 3.14.

• -Xcontext_aware_warnings=0,1 causes thewarnings.catch_warnings context manager to use aContextVar to store warnings filter state. Ifunset, the value of this option defaults to1 on free-threaded buildsand to0 otherwise. See alsoPYTHON_CONTEXT_AWARE_WARNINGS.

  Added in version 3.14.

• -Xtlbc=0,1 enables (1, the default) or disables (0) thread-localbytecode in builds configured with--disable-gil. When disabled,this also disables the specializing interpreter. See alsoPYTHON_TLBC.

  Added in version 3.14.

It also allows passing arbitrary values and retrieving them through thesys._xoptions dictionary.

Added in version 3.2.

Changed in version 3.9:Removed the-Xshowalloccount option.

Changed in version 3.10:Removed the-Xoldparser option.

1.1.4.Controlling color¶

The Python interpreter is configured by default to use colors to highlightoutput in certain situations such as when displaying tracebacks. Thisbehavior can be controlled by setting different environment variables.

Setting the environment variableTERM todumb will disable color.

If theFORCE_COLOR environment variable is set, then color will beenabled regardless of the value of TERM. This is useful on CI systems whicharen’t terminals but can still display ANSI escape sequences.

If theNO_COLOR environment variable is set, Python will disable all colorin the output. This takes precedence overFORCE_COLOR.

All these environment variables are used also by other tools to control coloroutput. To control the color output only in the Python interpreter, thePYTHON_COLORS environment variable can be used. This variable takesprecedence overNO_COLOR, which in turn takes precedence overFORCE_COLOR.

1.2.1.Debug-mode variables¶

PYTHONDUMPREFS¶

If set, Python will dump objects and reference counts still alive aftershutting down the interpreter.

Needs Python configured with the--with-trace-refs build option.

PYTHONDUMPREFSFILE¶

If set, Python will dump objects and reference counts still aliveafter shutting down the interpreter into a file under the path givenas the value to this environment variable.

Needs Python configured with the--with-trace-refs build option.

Added in version 3.11.

PYTHON_PRESITE¶

If this variable is set to a module, that module will be importedearly in the interpreter lifecycle, before thesite module isexecuted, and before the__main__ module is created.Therefore, the imported module is not treated as__main__.

This can be used to execute code early during Python initialization.

To import a submodule, usepackage.module as the value, like inan import statement.

See also the-Xpresite command-line option,which takes precedence over this variable.

Needs Python configured with the--with-pydebug build option.

Added in version 3.13.