1.Command line and environment¶

The CPython interpreter scans the command line and the environment for various settings.

CPython implementation detail:Other implementations’ command line schemes may differ. See Alternate Implementationsfor 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 some additional methods of invocation:

When called with standard input connected to a tty device, it prompts for commands and executes them until an EOF (an end-of-file character, you can produce that withCtrl-Don UNIX orCtrl-Z,Enteron Windows) is read. For more on interactive mode, seeInteractive Mode.
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 a directory name argument, it reads and executes an appropriately named script from that directory.
When called with-ccommand,it executes the Python statement(s) given as command.Herecommandmay contain multiple statements separated by newlines. Leading whitespace is significant in Python statements!
When called with-mmodule-name,the given module is located on the Python 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 first element, subscript zero (sys.argv[0]), is a string reflecting the program’s source.

-c<command>¶

Execute the Python code incommand.commandcan be one or more statements separated by newlines, with significant leading whitespace as in normal module code.

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

Raises anauditing eventcpython.run_commandwith argumentcommand.

-m<module-name>¶

Searchsys.pathfor the named module and execute its contents as the__main__module.

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

Package names (including namespace packages) are also permitted. When a package name is supplied instead of a normal module, the interpreter will execute<pkg>.__main__as the main module. This behaviour is deliberately similar to the handling of directories and zipfiles that are passed to the interpreter as the script argument.

Note

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

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

-Ioption can be used to run the script in isolated mode where sys.pathcontains neither the current directory nor the user’s site-packages directory. AllPYTHON*environment variables are ignored, too.

Many standard library modules contain code that is invoked on their execution as a script. An example is thetimeitmodule:

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

Raises anauditing eventcpython.run_modulewith 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 is a terminal,-iis implied.

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

Raises anauditing eventcpython.run_stdinwith no arguments.

<script>

Execute the Python code contained inscript,which must be a filesystem path (absolute or relative) referring to either a Python file, a directory containing a__main__.pyfile, or a zipfile containing a __main__.pyfile.

If this option is given, the first element ofsys.argvwill be the script name as given on the command line.

If the script name refers directly to a Python file, the directory containing that file is added to the start ofsys.path,and the file is executed as the__main__module.

If the script name refers to a directory or zipfile, the script name is added to the start ofsys.pathand the__main__.pyfile in that location is executed as the__main__module.

-Ioption can be used to run the script in isolated mode where sys.pathcontains neither the script’s directory nor the user’s site-packages directory. AllPYTHON*environment variables are ignored, too.

Raises anauditing eventcpython.run_filewith argumentfilename.

See also

runpy.run_path(): Equivalent functionality directly available to Python code

If no interface option is given,-iis implied,sys.argv[0]is an empty string ("") and the current directory will be added to the start ofsys.path.Also, tab-completion and history editing is automatically enabled, if available on your platform (see Readline 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 corresponding environment variables and exit.

--help-env¶: Print a short description of Python-specific environment variables and exit.

Added in version 3.11.

--help-xoptions¶: Print a description of implementation-specific-Xoptions and 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-VVoption.

1.1.3.Miscellaneous options¶

-b¶: Issue a warning when convertingbytesorbytearrayto strwithout specifying encoding or comparingbytesor bytearraywithstrorbyteswithint. Issue an error when the option is given twice (-bb).

Changed in version 3.5:Affects also comparisons ofbyteswithint.

-B¶: If given, Python won’t try to write.pycfiles on the import of source modules. See alsoPYTHONDONTWRITEBYTECODE.

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

Control the validation behavior of hash-based.pycfiles. See Cached bytecode invalidation.When set todefault,checked and unchecked hash-based bytecode cache files are validated according to their default semantics. When set toalways,all hash-based.pycfiles, whether checked or unchecked, are validated against their corresponding source file. When set tonever,hash-based.pycfiles are not validated against their corresponding source files.

The semantics of timestamp-based.pycfiles are unaffected by this option.

-d¶

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

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

-E¶

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

See also the-Pand-I(isolated) options.

-i¶

When a script is passed as first argument or the-coption is used, enter interactive mode after executing the script or the command, even when sys.stdindoes not appear to be a terminal. The PYTHONSTARTUPfile is not read.

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

-I¶

Run Python in isolated mode. This also implies-E,-P and-soptions.

In isolated modesys.pathcontains neither the script’s directory nor the user’s site-packages directory. AllPYTHON*environment variables are ignored, too. Further restrictions may be imposed to prevent the 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-1before the.pyc extension (seePEP 488). See alsoPYTHONOPTIMIZE.

Changed in version 3.5:Modify.pycfilenames according toPEP 488.

-OO¶: Do-Oand also discard docstrings. Augment the filename for compiled (bytecode) files by adding.opt-2before the .pycextension (seePEP 488).

Changed in version 3.5:Modify.pycfilenames according toPEP 488.

-P¶

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

python-mmodulecommand line: Don’t prepend the current working directory.
pythonscript.pycommand line: Don’t prepend the script’s directory. If it’s a symbolic link, resolve symbolic links.
python-ccodeandpython(REPL) command lines: Don’t prepend an empty string, which means the current working directory.

See also thePYTHONSAFEPATHenvironment variable, and-E and-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 the PYTHONHASHSEEDenvironment variable is set to0,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 objects are “salted” with an unpredictable random value. Although they remain constant within an individual Python process, they are not predictable between repeated invocations of Python.

Hash randomization is intended to provide protection against a denial-of-service caused by carefully chosen inputs that exploit the worst case performance of a dict construction,O(n²) complexity. See http://ocert.org/advisories/ocert-2011-003.htmlfor details.

PYTHONHASHSEEDallows you to set a fixed value for the hash seed secret.

Added in version 3.2.3.

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

-s¶

Don’t add theusersite-packagesdirectoryto sys.path.

See also

PEP 370– Per user site-packages directory

-S¶: Disable the import of the modulesiteand the site-dependent manipulations ofsys.paththat it entails. Also disable these manipulations ifsiteis explicitly imported later (call site.main()if you want them to be triggered).

-u¶

Force the stdout and stderr streams to be unbuffered. This option has no effect on the stdin stream.

1.1.4.Controlling color¶

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

Setting the environment variableTERMtodumbwill disable color.

If theFORCE_COLORenvironment variable is set, then color will be enabled regardless of the value of TERM. This is useful on CI systems which aren’t terminals but can still display ANSI escape sequences.

If theNO_COLORenvironment variable is set, Python will disable all color in the output. This takes precedence overFORCE_COLOR.

All these environment variables are used also by other tools to control color output. To control the color output only in the Python interpreter, the PYTHON_COLORSenvironment variable can be used. This variable takes precedence overNO_COLOR,which in turn takes precedence over FORCE_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 processed before the command-line switches other than -E or -I. It is customary that command-line switches override environmental variables where there is a conflict.

PYTHONHOME¶

Change the location of the standard Python libraries. By default, the libraries are searched inprefix/lib/pythonversionand exec_prefix/lib/pythonversion,whereprefixand exec_prefixare installation-dependent directories, both defaulting to/usr/local.

WhenPYTHONHOMEis set to a single directory, its value replaces bothprefixandexec_prefix.To specify different values for these, setPYTHONHOMEtoprefix:exec_prefix.

PYTHONPATH¶

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

In addition to normal directories, individualPYTHONPATHentries may refer to zipfiles containing pure Python modules (in either source or compiled form). Extension modules cannot be imported from zipfiles.

The default search path is installation dependent, but generally begins with prefix/lib/pythonversion(seePYTHONHOMEabove). It isalwaysappended toPYTHONPATH.

An additional directory will be inserted in the search path in front of PYTHONPATHas described above under Interface options.The search path can be manipulated from within a Python program as the variablesys.path.

PYTHONSAFEPATH¶: If this is set to a non-empty string, don’t prepend a potentially unsafe path tosys.path:see the-Poption for details.

Added in version 3.11.

PYTHONPLATLIBDIR¶: If this is set to a non-empty string, it overrides thesys.platlibdir value.

Added in version 3.9.

PYTHONSTARTUP¶

If this is the name of a readable file, the Python commands in that file are executed before the first prompt is displayed in interactive mode. The file is executed in the same namespace where interactive commands are executed so that objects defined or imported in it can be used without qualification in the interactive session. You can also change the promptssys.ps1and sys.ps2and the hooksys.__interactivehook__in this file.

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

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

PYTHONBREAKPOINT¶: If this is set, it names a callable using dotted-path notation. The module containing the callable will be imported and then the callable will be run by the default implementation ofsys.breakpointhook()which itself is called by built-inbreakpoint().If not set, or set to the empty string, it is equivalent to the value “pdb.set_trace”. Setting this to the string “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 -doption. If set to an integer, it is equivalent to specifying -dmultiple 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 -ioption.

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

Raises anauditing eventcpython.run_stdinwith 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 casePYTHONSTARTUPis also executed. Emits audit events.

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

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

PYTHONCASEOK¶: If this is set, Python ignores case inimportstatements. This only works on Windows and macOS.

PYTHONDONTWRITEBYTECODE¶: If this is set to a non-empty string, Python won’t try to write.pyc files on the import of source modules. This is equivalent to specifying the-Boption.

PYTHONPYCACHEPREFIX¶: If this is set, Python will write.pycfiles in a mirror directory tree at this path, instead of in__pycache__directories within the source tree. This is equivalent to specifying the-X pycache_prefix=PATHoption.

Added in version 3.8.

PYTHONHASHSEED¶

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

IfPYTHONHASHSEEDis set to an integer value, it is used as a fixed seed for generating the hash() of the types covered by the hash randomization.

Its purpose is to allow repeatable hashing, such as for selftests for the interpreter itself, or to allow a cluster of python processes to share hash values.

The integer must be a decimal number in the range [0,4294967295]. Specifying the 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 the interpreter’s globalinteger string conversion length limitation.

Added in version 3.11.

PYTHONIOENCODING¶

If this is set before running the interpreter, it overrides the encoding used for stdin/stdout/stderr, in the syntaxencodingname:errorhandler.Both theencodingnameand the:errorhandlerparts are optional and have the same meaning as instr.encode().

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

Changed in version 3.4:Theencodingnamepart is now optional.

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

PYTHONNOUSERSITE¶: If this is set, Python won’t add theusersite-packagesdirectorytosys.path.

See also

PEP 370– Per user site-packages directory

PYTHONUSERBASE¶: Defines theuserbasedirectory,which is used to compute the path of theusersite-packagesdirectory andinstallation pathsfor python-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 its value instead of the value got through the C runtime. Only works on macOS.

PYTHONWARNINGS¶

This is equivalent to the-Woption. If set to a comma separated string, it is equivalent to specifying-Wmultiple times, with filters later in the list taking precedence over those earlier in the list.

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

PYTHONWARNINGS=default# Warn once per call location
PYTHONWARNINGS=error# Convert to exceptions
PYTHONWARNINGS=always# Warn every time
PYTHONWARNINGS=all# Same as PYTHONWARNINGS=always
PYTHONWARNINGS=module# Warn once per calling module
PYTHONWARNINGS=once# Warn once per Python process
PYTHONWARNINGS=ignore# Never warn

SeeThe Warnings FilterandDescribing Warning Filtersfor more details.

PYTHONFAULTHANDLER¶: If this environment variable is set to a non-empty string, faulthandler.enable()is called at startup: install a handler for SIGSEGV,SIGFPE, SIGABRT,SIGBUSand SIGILLsignals to dump the Python traceback. This is equivalent to-Xfaulthandleroption.

Added in version 3.3.

PYTHONTRACEMALLOC¶: If this environment variable is set to a non-empty string, start tracing Python memory allocations using thetracemallocmodule. The value of the variable is the maximum number of frames stored in a traceback of a trace. For example,PYTHONTRACEMALLOC=1stores only the most recent frame. See thetracemalloc.start()function for more information. This is equivalent to setting the-Xtracemallocoption.

Added in version 3.4.

PYTHONPROFILEIMPORTTIME¶: If this environment variable is set to a non-empty string, Python will show how long each import takes. This is equivalent to setting the-Ximporttimeoption.

Added in version 3.7.

PYTHONASYNCIODEBUG¶: If this environment variable is set to a non-empty string, enable the debug modeof theasynciomodule.

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 library for all domains (PYMEM_DOMAIN_RAW,PYMEM_DOMAIN_MEM, PYMEM_DOMAIN_OBJ).
pymalloc:use thepymalloc allocatorfor PYMEM_DOMAIN_MEMandPYMEM_DOMAIN_OBJdomains and use themalloc()function for thePYMEM_DOMAIN_RAWdomain.
mimalloc:use themimalloc allocatorfor PYMEM_DOMAIN_MEMandPYMEM_DOMAIN_OBJdomains and use themalloc()function for thePYMEM_DOMAIN_RAWdomain.

Installdebug hooks:

debug:install debug hooks on top of thedefault memory allocators.
malloc_debug:same asmallocbut also install debug hooks.
pymalloc_debug:same aspymallocbut also install debug hooks.
mimalloc_debug:same asmimallocbut 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 the pymalloc memory allocatorevery time a new pymalloc object arena is created, and on shutdown.

This variable is ignored if thePYTHONMALLOCenvironment variable is used to force themalloc()allocator of the C library, or if Python is configured withoutpymallocsupport.

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 and error handlermode 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 with sys._enablelegacywindowsfsencoding().

Availability:Windows.

Added in version 3.6:SeePEP 529for more details.

PYTHONLEGACYWINDOWSSTDIO¶

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

This variable is ignored if the standard streams are redirected (to files or 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 application to skip coercing the legacy ASCII-based C and POSIX locales to a more capable UTF-8 based alternative.

If this variable isnotset (or is set to a value other than0), the LC_ALLlocale override environment variable is also not set, and the current locale reported for theLC_CTYPEcategory is either the default Clocale, or else the explicitly ASCII-basedPOSIXlocale, then the Python CLI will attempt to configure the following locales for the LC_CTYPEcategory in the order listed before loading the interpreter runtime:

C.UTF-8
C.utf8
UTF-8

If setting one of these locale categories succeeds, then theLC_CTYPE environment variable will also be set accordingly in the current process environment before the Python runtime is initialized. This ensures that in addition to being seen by both the interpreter itself and other locale-aware components running in the same process (such as the GNUreadline library), the updated setting is also seen in subprocesses (regardless of whether or not those processes are running a Python interpreter), as well as in 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 above implicit locale coercion) automatically enables thesurrogateescape error handlerforsys.stdinand sys.stdout(sys.stderrcontinues to usebackslashreplace as it does in any other locale). This stream handling behavior can be overridden usingPYTHONIOENCODINGas usual.

For debugging purposes, settingPYTHONCOERCECLOCALE=warnwill cause Python to emit warning messages onstderrif either the locale coercion activates, or else if a locale thatwouldhave triggered coercion is still active when the Python runtime is initialized.

Also note that even when locale coercion is disabled, or when it fails to find a suitable target locale,PYTHONUTF8will still activate by default in legacy ASCII-based locales. Both features must be disabled in order to force the interpreter to useASCIIinstead ofUTF-8for system interfaces.

Availability:Unix.

Added in version 3.7:SeePEP 538for more details.

PYTHONDEVMODE¶: If this environment variable is set to a non-empty string, enable Python Development Mode,introducing additional runtime checks that are too expensive to be enabled by default. This is equivalent to setting the-Xdevoption.

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 interpreter initialisation.

Added in version 3.7.

PYTHONWARNDEFAULTENCODING¶

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

SeeOpt-in EncodingWarningfor details.

Added in version 3.10.

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

Added in version 3.11.

PYTHONPERFSUPPORT¶

If this variable is set to a nonzero value, it enables support for the Linuxperfprofiler so Python calls can be detected by it.

If set to0,disable Linuxperfprofiler support.

See also the-Xperfcommand-line option andPython 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 for the Linuxperfprofiler so Python calls can be detected by it using DWARF information.

If set to0,disable Linuxperfprofiler support.

See also the-Xperf_jitcommand-line option andPython 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 return values ofos.cpu_count()andos.process_cpu_count().

See also the-Xcpu_countcommand-line option.

Added in version 3.13.

PYTHON_FROZEN_MODULES¶

If this variable is set toonoroff,it determines whether or not frozen modules are ignored by the import machinery. A value ofonmeans they get imported andoffmeans they are ignored. The default ison for non-debug builds (the normal case) andofffor debug builds. Note that theimportlib_bootstrapand importlib_bootstrap_externalfrozen modules are always used, even if this flag is set tooff.

See also the-Xfrozen_modulescommand-line option.

Added in version 3.13.

PYTHON_COLORS¶: If this variable is set to1,the interpreter will colorize various kinds of output. Setting it to0deactivates this behavior. See alsoControlling color.

Added in version 3.13.

PYTHON_BASIC_REPL¶: If this variable is set to1,the interpreter will not attempt to load the Python-basedREPLthat requirescursesand readline,and will instead use the traditional parser-based REPL.

Added in version 3.13.

PYTHON_HISTORY¶: This environment variable can be used to set the location of a .python_historyfile (by default, it is.python_historyin the user’s home directory).

Added in version 3.13.

PYTHON_GIL¶

If this variable is set to1,the global interpreter lock (GIL) will be forced on. Setting it to0forces the GIL off (needs Python configured with the--disable-gilbuild option).

See also the-Xgilcommand-line option, which takes precedence over this variable, andFree-threaded CPython.

Added in version 3.13.

1.2.1.Debug-mode variables¶

PYTHONDUMPREFS¶

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

Needs Python configured with the--with-trace-refsbuild option.

PYTHONDUMPREFSFILE¶

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

Needs Python configured with the--with-trace-refsbuild option.

Added in version 3.11.

PYTHON_PRESITE¶

If this variable is set to a module, that module will be imported early in the interpreter lifecycle, before thesitemodule is executed, 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.moduleas the value, like in an import statement.

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

Needs Python configured with the--with-pydebugbuild option.

Added in version 3.13.

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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