1.Command line and environment¶

The CPython interpreter scans the command line and the environment for varioussettings.

CPython implementation detail: Other implementations’ command line schemes may differ. SeeAlternate Implementations for further resources.

1.1.Command line¶

When invoking Python, you may specify any of these options:

python[-bBdEhiIOPqRsSuvVWx?][-ccommand|-mmodule-name|script|-][args]

The most common use case is, of course, a simple invocation of a script:

pythonmyscript.py

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.

-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).

See also

Invoking the Interpreter

Changed in version 3.4:Automatic enabling of tab-completion and history editing.

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 to0, since hashrandomization 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 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.

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.

1.1.5.Options you shouldn’t use¶

-J¶: Reserved for use byJython.

1.2.Environment variables¶

These environment variables influence Python’s behavior, they are processedbefore the command-line switches other than -E or -I. It is customary thatcommand-line switches override environmental variables where there is aconflict.

PYTHONHOME¶

Change the location of the standard Python libraries. By default, thelibraries are searched inprefix/lib/pythonversion andexec_prefix/lib/pythonversion, whereprefix andexec_prefix are installation-dependent directories, both defaultingto/usr/local.

WhenPYTHONHOME is set to a single directory, its value replacesbothprefix andexec_prefix. To specify different valuesfor these, setPYTHONHOME toprefix:exec_prefix.

PYTHONPATH¶

Augment the default search path for module files. The format is the same asthe shell’sPATH: one or more directory pathnames separated byos.pathsep (e.g. colons on Unix or semicolons on Windows).Non-existent directories are silently ignored.

In addition to normal directories, individualPYTHONPATH entriesmay refer to zipfiles containing pure Python modules (in either source orcompiled form). Extension modules cannot be imported from zipfiles.

The default search path is installation dependent, but generally begins withprefix/lib/pythonversion (seePYTHONHOME above). Itisalways appended toPYTHONPATH.

An additional directory will be inserted in the search path in front ofPYTHONPATH as described above underInterface options. The search path can be manipulated fromwithin a Python program as the variablesys.path.

PYTHONSAFEPATH¶: If this is set to a non-empty string, don’t prepend a potentially unsafepath tosys.path: see the-P option for details.
Added in version 3.11.

PYTHONPLATLIBDIR¶: If this is set to a non-empty string, it overrides thesys.platlibdirvalue.
Added in version 3.9.

PYTHONSTARTUP¶

If this is the name of a readable file, the Python commands in that file areexecuted before the first prompt is displayed in interactive mode. The fileis executed in the same namespace where interactive commands are executed sothat objects defined or imported in it can be used without qualification inthe interactive session. You can also change the promptssys.ps1 andsys.ps2 and the hooksys.__interactivehook__ in this file.

Raises anauditing eventcpython.run_startup withthe filename as the argument when called on startup.

PYTHONOPTIMIZE¶: If this is set to a non-empty string it is equivalent to specifying the-O option. If set to an integer, it is equivalent to specifying-O multiple times.

PYTHONBREAKPOINT¶: If this is set, it names a callable using dotted-path notation. The modulecontaining the callable will be imported and then the callable will be runby the default implementation ofsys.breakpointhook() which itself iscalled by built-inbreakpoint(). If not set, or set to the emptystring, it is equivalent to the value “pdb.set_trace”. Setting this to thestring “0” causes the default implementation ofsys.breakpointhook()to do nothing but return immediately.
Added in version 3.7.

PYTHONDEBUG¶

If this is set to a non-empty string it is equivalent to specifying the-d option. If set to an integer, it is equivalent to specifying-d multiple times.

This environment variable requires adebug build of Python, otherwise it’s ignored.

PYTHONINSPECT¶

If this is set to a non-empty string it is equivalent to specifying the-i option.

This variable can also be modified by Python code usingos.environto force inspect mode on program termination.

Raises anauditing eventcpython.run_stdin with no arguments.

Changed in version 3.12.5:(also 3.11.10, 3.10.15, 3.9.20, and 3.8.20)Emits audit events.

Changed in version 3.13:Uses PyREPL if possible, in which casePYTHONSTARTUP isalso executed. Emits audit events.

PYTHONUNBUFFERED¶: If this is set to a non-empty string it is equivalent to specifying the-u option.

PYTHONVERBOSE¶: If this is set to a non-empty string it is equivalent to specifying the-v option. If set to an integer, it is equivalent to specifying-v multiple times.

PYTHONCASEOK¶: If this is set, Python ignores case inimport statements. Thisonly works on Windows and macOS.

PYTHONDONTWRITEBYTECODE¶: If this is set to a non-empty string, Python won’t try to write.pycfiles on the import of source modules. This is equivalent tospecifying the-B option.

PYTHONPYCACHEPREFIX¶: If this is set, Python will write.pyc files in a mirror directory treeat this path, instead of in__pycache__ directories within the sourcetree. This is equivalent to specifying the-Xpycache_prefix=PATH option.
Added in version 3.8.

PYTHONHASHSEED¶

If this variable is not set or set torandom, a random value is usedto seed the hashes of str and bytes objects.

IfPYTHONHASHSEED is set to an integer value, it is used as a fixedseed for generating the hash() of the types covered by the hashrandomization.

Its purpose is to allow repeatable hashing, such as for selftests for theinterpreter itself, or to allow a cluster of python processes to share hashvalues.

The integer must be a decimal number in the range [0,4294967295]. Specifyingthe value 0 will disable hash randomization.

Added in version 3.2.3.

PYTHONINTMAXSTRDIGITS¶: If this variable is set to an integer, it is used to configure theinterpreter’s globalinteger string conversion length limitation.
Added in version 3.11.

PYTHONIOENCODING¶

If this is set before running the interpreter, it overrides the encoding usedfor stdin/stdout/stderr, in the syntaxencodingname:errorhandler. Boththeencodingname and the:errorhandler parts are optional and havethe same meaning as instr.encode().

For stderr, the:errorhandler part is ignored; the handler will always be'backslashreplace'.

Changed in version 3.4:Theencodingname part is now optional.

Changed in version 3.6:On Windows, the encoding specified by this variable is ignored for interactiveconsole buffers unlessPYTHONLEGACYWINDOWSSTDIO is also specified.Files and pipes redirected through the standard streams are not affected.

PYTHONNOUSERSITE¶: If this is set, Python won’t add theusersite-packagesdirectory tosys.path.
See also
PEP 370 – Per user site-packages directory

PYTHONUSERBASE¶: Defines theuserbasedirectory, which is used tocompute the path of theusersite-packagesdirectoryandinstallation paths forpython-mpipinstall--user.
See also
PEP 370 – Per user site-packages directory

PYTHONEXECUTABLE¶: If this environment variable is set,sys.argv[0] will be set to itsvalue instead of the value got through the C runtime. Only works onmacOS.

PYTHONWARNINGS¶

This is equivalent to the-W option. If set to a commaseparated string, it is equivalent to specifying-W multipletimes, with filters later in the list taking precedence over those earlierin the list.

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

PYTHONWARNINGS=default# Warn once per call locationPYTHONWARNINGS=error# Convert to exceptionsPYTHONWARNINGS=always# Warn every timePYTHONWARNINGS=all# Same as PYTHONWARNINGS=alwaysPYTHONWARNINGS=module# Warn once per calling modulePYTHONWARNINGS=once# Warn once per Python processPYTHONWARNINGS=ignore# Never warn

SeeThe Warnings Filter andDescribing Warning Filters for moredetails.

PYTHONFAULTHANDLER¶: If this environment variable is set to a non-empty string,faulthandler.enable() is called at startup: install a handler forSIGSEGV,SIGFPE,SIGABRT,SIGBUS andSIGILL signals to dump the Python traceback.This is equivalent to-Xfaulthandler option.
Added in version 3.3.

PYTHONTRACEMALLOC¶: If this environment variable is set to a non-empty string, start tracingPython memory allocations using thetracemalloc module. The value ofthe variable is the maximum number of frames stored in a traceback of atrace. For example,PYTHONTRACEMALLOC=1 stores only the most recentframe.See thetracemalloc.start() function for more information.This is equivalent to setting the-Xtracemalloc option.
Added in version 3.4.

PYTHONPROFILEIMPORTTIME¶: If this environment variable is set to a non-empty string, Python willshow how long each import takes.This is equivalent to setting the-Ximporttime option.
Added in version 3.7.

PYTHONASYNCIODEBUG¶: If this environment variable is set to a non-empty string, enable thedebug mode of theasyncio module.
Added in version 3.4.

PYTHONMALLOC¶

Set the Python memory allocators and/or install debug hooks.

Set the family of memory allocators used by Python:

default: use thedefault memory allocators.
malloc: use themalloc() function of the C libraryfor all domains (PYMEM_DOMAIN_RAW,PYMEM_DOMAIN_MEM,PYMEM_DOMAIN_OBJ).
pymalloc: use thepymalloc allocator forPYMEM_DOMAIN_MEM andPYMEM_DOMAIN_OBJ domains and usethemalloc() function for thePYMEM_DOMAIN_RAW domain.
mimalloc: use themimalloc allocator forPYMEM_DOMAIN_MEM andPYMEM_DOMAIN_OBJ domains and usethemalloc() function for thePYMEM_DOMAIN_RAW domain.

Installdebug hooks:

debug: install debug hooks on top of thedefault memoryallocators.
malloc_debug: same asmalloc but also install debug hooks.
pymalloc_debug: same aspymalloc but also install debug hooks.
mimalloc_debug: same asmimalloc but also install debug hooks.

Added in version 3.6.

Changed in version 3.7:Added the"default" allocator.

PYTHONMALLOCSTATS¶

If set to a non-empty string, Python will print statistics of thepymalloc memory allocator every time a new pymalloc objectarena is created, and on shutdown.

This variable is ignored if thePYTHONMALLOC environment variableis used to force themalloc() allocator of the C library, or ifPython is configured withoutpymalloc support.

Changed in version 3.6:This variable can now also be used on Python compiled in release mode.It now has no effect if set to an empty string.

PYTHONLEGACYWINDOWSFSENCODING¶

If set to a non-empty string, the defaultfilesystem encoding anderror handler mode will revert to their pre-3.6 values of ‘mbcs’ and‘replace’, respectively. Otherwise, the new defaults ‘utf-8’ and‘surrogatepass’ are used.

This may also be enabled at runtime withsys._enablelegacywindowsfsencoding().

Availability: Windows.

Added in version 3.6:SeePEP 529 for more details.

PYTHONLEGACYWINDOWSSTDIO¶

If set to a non-empty string, does not use the new console reader andwriter. This means that Unicode characters will be encoded according tothe active console code page, rather than using utf-8.

This variable is ignored if the standard streams are redirected (to filesor pipes) rather than referring to console buffers.

Availability: Windows.

Added in version 3.6.

PYTHONCOERCECLOCALE¶

If set to the value0, causes the main Python command line applicationto skip coercing the legacy ASCII-based C and POSIX locales to a morecapable UTF-8 based alternative.

If this variable isnot set (or is set to a value other than0), theLC_ALL locale override environment variable is also not set, and thecurrent locale reported for theLC_CTYPE category is either the defaultC locale, or else the explicitly ASCII-basedPOSIX locale, then thePython CLI will attempt to configure the following locales for theLC_CTYPE category in the order listed before loading the interpreterruntime:

C.UTF-8
C.utf8
UTF-8

If setting one of these locale categories succeeds, then theLC_CTYPEenvironment variable will also be set accordingly in the current processenvironment before the Python runtime is initialized. This ensures that inaddition to being seen by both the interpreter itself and other locale-awarecomponents running in the same process (such as the GNUreadlinelibrary), the updated setting is also seen in subprocesses (regardless ofwhether or not those processes are running a Python interpreter), as well asin operations that query the environment rather than the current C locale(such as Python’s ownlocale.getdefaultlocale()).

Configuring one of these locales (either explicitly or via the aboveimplicit locale coercion) automatically enables thesurrogateescapeerror handler forsys.stdin andsys.stdout (sys.stderr continues to usebackslashreplaceas it does in any other locale). This stream handling behavior can beoverridden usingPYTHONIOENCODING as usual.

For debugging purposes, settingPYTHONCOERCECLOCALE=warn will causePython to emit warning messages onstderr if either the locale coercionactivates, or else if a locale thatwould have triggered coercion isstill active when the Python runtime is initialized.

Also note that even when locale coercion is disabled, or when it fails tofind a suitable target locale,PYTHONUTF8 will still activate bydefault in legacy ASCII-based locales. Both features must be disabled inorder to force the interpreter to useASCII instead ofUTF-8 forsystem interfaces.

Availability: Unix.

Added in version 3.7:SeePEP 538 for more details.

PYTHONDEVMODE¶: If this environment variable is set to a non-empty string, enablePython Development Mode, introducing additional runtimechecks that are too expensive to be enabled by default.This is equivalent to setting the-Xdev option.
Added in version 3.7.

PYTHONUTF8¶

If set to1, enable thePython UTF-8 Mode.

If set to0, disable thePython UTF-8 Mode.

Setting any other non-empty string causes an error during interpreterinitialisation.

Added in version 3.7.

PYTHONWARNDEFAULTENCODING¶

If this environment variable is set to a non-empty string, issue aEncodingWarning when the locale-specific default encoding is used.

SeeOpt-in EncodingWarning for details.

Added in version 3.10.

PYTHONNODEBUGRANGES¶: If this variable is set, it disables the inclusion of the tables mappingextra location information (end line, start column offset and end columnoffset) to every instruction in code objects. This is useful when smallercode objects and pyc files are desired as well as suppressing the extra visuallocation indicators when the interpreter displays tracebacks.
Added in version 3.11.

PYTHONPERFSUPPORT¶

If this variable is set to a nonzero value, it enables support forthe Linuxperf profiler so Python calls can be detected by it.

If set to0, disable Linuxperf profiler support.

See also the-Xperf command-line optionandPython support for the Linux perf profiler.

Added in version 3.12.

PYTHON_PERF_JIT_SUPPORT¶

If this variable is set to a nonzero value, it enables support forthe Linuxperf profiler so Python calls can be detected by itusing DWARF information.

If set to0, disable Linuxperf profiler support.

See also the-Xperf_jit command-line optionandPython support for the Linux perf profiler.

Added in version 3.13.

PYTHON_CPU_COUNT¶

If this variable is set to a positive integer, it overrides the returnvalues ofos.cpu_count() andos.process_cpu_count().

See also the-Xcpu_count command-line option.

Added in version 3.13.

PYTHON_FROZEN_MODULES¶

If this variable is set toon oroff, it determines whether or notfrozen modules are ignored by the import machinery. A value ofon meansthey get imported andoff means they are ignored. The default isonfor non-debug builds (the normal case) andoff for debug builds.Note that theimportlib_bootstrap andimportlib_bootstrap_external frozen modules are always used, evenif this flag is set tooff.

See also the-Xfrozen_modules command-line option.

Added in version 3.13.

PYTHON_COLORS¶: If this variable is set to1, the interpreter will colorize various kindsof output. Setting it to0 deactivates this behavior.See alsoControlling color.
Added in version 3.13.

PYTHON_BASIC_REPL¶: If this variable is set to any value, the interpreter will not attempt toload the Python-basedREPL that requirescurses andreadline, and will instead use the traditional parser-basedREPL.
Added in version 3.13.

PYTHON_HISTORY¶: This environment variable can be used to set the location of a.python_history file (by default, it is.python_history in theuser’s home directory).
Added in version 3.13.

PYTHON_GIL¶

If this variable is set to1, the global interpreter lock (GIL) will beforced on. Setting it to0 forces the GIL off (needs Python configured withthe--disable-gil build option).

See also the-Xgil command-line option, which takesprecedence over this variable, andFree-threaded CPython.

Added in version 3.13.

PYTHON_JIT¶: On builds where experimental just-in-time compilation is available, thisvariable can force the JIT to be disabled (0) or enabled (1) atinterpreter startup.
Added in version 3.13.

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.

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1.Command line and environment¶

1.1.Command line¶

1.1.1.Interface options¶

1.1.2.Generic options¶

1.1.3.Miscellaneous options¶

1.1.4.Controlling color¶

1.1.5.Options you shouldn’t use¶

1.2.Environment variables¶

1.2.1.Debug-mode variables¶

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