sys— System-specific parameters and functions

---

This module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter. It is always available.

sys.abiflags

On POSIX systems where Python was built with the standardconfigure script, this contains the ABI flags as specified byPEP 3149.

Added in version 3.2.

Changed in version 3.8:Default flags became an empty string (mflag for pymalloc has been removed).

Availability:Unix.

sys.addaudithook(hook)

Append the callablehookto the list of active auditing hooks for the current (sub)interpreter.

When an auditing event is raised through thesys.audit()function, each hook will be called in the order it was added with the event name and the tuple of arguments. Native hooks added byPySys_AddAuditHook()are called first, followed by hooks added in the current (sub)interpreter. Hooks can then log the event, raise an exception to abort the operation, or terminate the process entirely.

Note that audit hooks are primarily for collecting information about internal or otherwise unobservable actions, whether by Python or libraries written in Python. They are not suitable for implementing a “sandbox”. In particular, malicious code can trivially disable or bypass hooks added using this function. At a minimum, any security-sensitive hooks must be added using the C APIPySys_AddAuditHook()before initialising the runtime, and any modules allowing arbitrary memory modification (such asctypes) should be completely removed or closely monitored.

Callingsys.addaudithook()will itself raise an auditing event namedsys.addaudithookwith no arguments. If any existing hooks raise an exception derived fromRuntimeError,the new hook will not be added and the exception suppressed. As a result, callers cannot assume that their hook has been added unless they control all existing hooks.

See theaudit events tablefor all events raised by CPython, andPEP 578for the original design discussion.

Added in version 3.8.

Changed in version 3.8.1:Exceptions derived fromExceptionbut notRuntimeError are no longer suppressed.

CPython implementation detail:When tracing is enabled (seesettrace()), Python hooks are only traced if the callable has a__cantrace__member that is set to a true value. Otherwise, trace functions will skip the hook.

sys.argv

The list of command line arguments passed to a Python script.argv[0]is the script name (it is operating system dependent whether this is a full pathname or not). If the command was executed using the-ccommand line option to the interpreter,argv[0]is set to the string'-c'.If no script name was passed to the Python interpreter,argv[0]is the empty string.

To loop over the standard input, or the list of files given on the command line, see thefileinputmodule.

See alsosys.orig_argv.

Note

On Unix, command line arguments are passed by bytes from OS. Python decodes them with filesystem encoding and “surrogateescape” error handler. When you need original bytes, you can get it by [os.fsencode(arg)forarginsys.argv].

sys.audit(event,*args)

Raise an auditing event and trigger any active auditing hooks. eventis a string identifying the event, andargsmay contain optional arguments with more information about the event. The number and types of arguments for a given event are considered a public and stable API and should not be modified between releases.

For example, one auditing event is namedos.chdir.This event has one argument calledpaththat will contain the requested new working directory.

sys.audit()will call the existing auditing hooks, passing the event name and arguments, and will re-raise the first exception from any hook. In general, if an exception is raised, it should not be handled and the process should be terminated as quickly as possible. This allows hook implementations to decide how to respond to particular events: they can merely log the event or abort the operation by raising an exception.

Hooks are added using thesys.addaudithook()or PySys_AddAuditHook()functions.

The native equivalent of this function isPySys_Audit().Using the native function is preferred when possible.

See theaudit events tablefor all events raised by CPython.

Added in version 3.8.

sys.base_exec_prefix

Set during Python startup, beforesite.pyis run, to the same value as exec_prefix.If not running in a virtual environment,the values will stay the same; if site.pyfinds that a virtual environment is in use, the values of prefixandexec_prefixwill be changed to point to the virtual environment, whereasbase_prefixand base_exec_prefixwill remain pointing to the base Python installation (the one which the virtual environment was created from).

Added in version 3.3.

sys.base_prefix

Set during Python startup, beforesite.pyis run, to the same value as prefix.If not running in avirtual environment,the values will stay the same; ifsite.pyfinds that a virtual environment is in use, the values ofprefixandexec_prefixwill be changed to point to the virtual environment, whereasbase_prefixand base_exec_prefixwill remain pointing to the base Python installation (the one which the virtual environment was created from).

Added in version 3.3.

sys.byteorder

An indicator of the native byte order. This will have the value'big'on big-endian (most-significant byte first) platforms, and'little'on little-endian (least-significant byte first) platforms.

sys.builtin_module_names

A tuple of strings containing the names of all modules that are compiled into this Python interpreter. (This information is not available in any other way — modules.keys()only lists the imported modules.)

See also thesys.stdlib_module_nameslist.

sys.call_tracing(func,args)

Callfunc(*args),while tracing is enabled. The tracing state is saved, and restored afterwards. This is intended to be called from a debugger from a checkpoint, to recursively debug or profile some other code.

Tracing is suspended while calling a tracing function set by settrace()orsetprofile()to avoid infinite recursion. call_tracing()enables explicit recursion of the tracing function.

sys.copyright

A string containing the copyright pertaining to the Python interpreter.

sys._clear_type_cache()

Clear the internal type cache. The type cache is used to speed up attribute and method lookups. Use the functiononlyto drop unnecessary references during reference leak debugging.

This function should be used for internal and specialized purposes only.

sys._current_frames()

Return a dictionary mapping each thread’s identifier to the topmost stack frame currently active in that thread at the time the function is called. Note that functions in thetracebackmodule can build the call stack given such a frame.

This is most useful for debugging deadlock: this function does not require the deadlocked threads’ cooperation, and such threads’ call stacks are frozen for as long as they remain deadlocked. The frame returned for a non-deadlocked thread may bear no relationship to that thread’s current activity by the time calling code examines the frame.

This function should be used for internal and specialized purposes only.

Raises anauditing eventsys._current_frameswith no arguments.

sys._current_exceptions()

Return a dictionary mapping each thread’s identifier to the topmost exception currently active in that thread at the time the function is called. If a thread is not currently handling an exception, it is not included in the result dictionary.

This is most useful for statistical profiling.

This function should be used for internal and specialized purposes only.

Raises anauditing eventsys._current_exceptionswith no arguments.

Changed in version 3.12:Each value in the dictionary is now a single exception instance, rather than a 3-tuple as returned fromsys.exc_info().

sys.breakpointhook()

This hook function is called by built-inbreakpoint().By default, it drops you into thepdbdebugger, but it can be set to any other function so that you can choose which debugger gets used.

The signature of this function is dependent on what it calls. For example, the default binding (e.g.pdb.set_trace()) expects no arguments, but you might bind it to a function that expects additional arguments (positional and/or keyword). The built-inbreakpoint()function passes its*argsand**kwsstraight through. Whatever breakpointhooks()returns is returned frombreakpoint().

The default implementation first consults the environment variable PYTHONBREAKPOINT.If that is set to"0"then this function returns immediately; i.e. it is a no-op. If the environment variable is not set, or is set to the empty string,pdb.set_trace()is called. Otherwise this variable should name a function to run, using Python’s dotted-import nomenclature, e.g.package.subpackage.module.function. In this case,package.subpackage.modulewould be imported and the resulting module must have a callable namedfunction().This is run, passing in*argsand**kws,and whateverfunction()returns, sys.breakpointhook()returns to the built-inbreakpoint() function.

Note that if anything goes wrong while importing the callable named by PYTHONBREAKPOINT,aRuntimeWarningis reported and the breakpoint is ignored.

Also note that ifsys.breakpointhook()is overridden programmatically, PYTHONBREAKPOINTisnotconsulted.

Added in version 3.7.

sys._debugmallocstats()

Print low-level information to stderr about the state of CPython’s memory allocator.

If Python isbuilt in debug mode(configure --with-pydebugoption), it also performs some expensive internal consistency checks.

Added in version 3.3.

CPython implementation detail:This function is specific to CPython. The exact output format is not defined here, and may change.

sys.dllhandle

Integer specifying the handle of the Python DLL.

Availability:Windows.

sys.displayhook(value)

Ifvalueis notNone,this function printsrepr(value)to sys.stdout,and savesvalueinbuiltins._.Ifrepr(value)is not encodable tosys.stdout.encodingwithsys.stdout.errorserror handler (which is probably'strict'), encode it to sys.stdout.encodingwith'backslashreplace'error handler.

sys.displayhookis called on the result of evaluating anexpression entered in an interactive Python session. The display of these values can be customized by assigning another one-argument function tosys.displayhook.

Pseudo-code:

defdisplayhook(value):
ifvalueisNone:
return
# Set '_' to None to avoid recursion
builtins._=None
text=repr(value)
try:
sys.stdout.write(text)
exceptUnicodeEncodeError:
bytes=text.encode(sys.stdout.encoding,'backslashreplace')
ifhasattr(sys.stdout,'buffer'):
sys.stdout.buffer.write(bytes)
else:
text=bytes.decode(sys.stdout.encoding,'strict')
sys.stdout.write(text)
sys.stdout.write("\n")
builtins._=value

Changed in version 3.2:Use'backslashreplace'error handler onUnicodeEncodeError.

sys.dont_write_bytecode

If this is true, Python won’t try to write.pycfiles on the import of source modules. This value is initially set toTrueor Falsedepending on the-Bcommand line option and the PYTHONDONTWRITEBYTECODEenvironment variable, but you can set it yourself to control bytecode file generation.

sys._emscripten_info

Anamed tupleholding information about the environment on the wasm32-emscriptenplatform. The named tuple is provisional and may change in the future.

_emscripten_info.emscripten_version

Emscripten version as tuple of ints (major, minor, micro), e.g.(3,1,8).

_emscripten_info.runtime

Runtime string, e.g. browser user agent,'Node.jsv14.18.2',or'UNKNOWN'.

_emscripten_info.pthreads

Trueif Python is compiled with Emscripten pthreads support.

_emscripten_info.shared_memory

Trueif Python is compiled with shared memory support.

Availability:Emscripten.

Added in version 3.11.

sys.pycache_prefix

If this is set (notNone), Python will write bytecode-cache.pyc files to (and read them from) a parallel directory tree rooted at this directory, rather than from__pycache__directories in the source code tree. Any__pycache__directories in the source code tree will be ignored and new.pycfiles written within the pycache prefix. Thus if you use compileallas a pre-build step, you must ensure you run it with the same pycache prefix (if any) that you will use at runtime.

A relative path is interpreted relative to the current working directory.

This value is initially set based on the value of the-X pycache_prefix=PATHcommand-line option or the PYTHONPYCACHEPREFIXenvironment variable (command-line takes precedence). If neither are set, it isNone.

Added in version 3.8.

sys.excepthook(type,value,traceback)

This function prints out a given traceback and exception tosys.stderr.

When an exception other thanSystemExitis raised and uncaught, the interpreter calls sys.excepthookwith three arguments, the exception class, exception instance, and a traceback object. In an interactive session this happens just before control is returned to the prompt; in a Python program this happens just before the program exits. The handling of such top-level exceptions can be customized by assigning another three-argument function tosys.excepthook.

Raise an auditing eventsys.excepthookwith argumentshook, type,value,tracebackwhen an uncaught exception occurs. If no hook has been set,hookmay beNone.If any hook raises an exception derived fromRuntimeErrorthe call to the hook will be suppressed. Otherwise, the audit hook exception will be reported as unraisable andsys.excepthookwill be called.

See also

Thesys.unraisablehook()function handles unraisable exceptions and thethreading.excepthook()function handles exception raised bythreading.Thread.run().

sys.__breakpointhook__

sys.__displayhook__

sys.__excepthook__

sys.__unraisablehook__

These objects contain the original values ofbreakpointhook, displayhook,excepthook,andunraisablehookat the start of the program. They are saved so thatbreakpointhook,displayhookand excepthook,unraisablehookcan be restored in case they happen to get replaced with broken or alternative objects.

Added in version 3.7:__breakpointhook__

Added in version 3.8:__unraisablehook__

sys.exception()

This function, when called while an exception handler is executing (such as anexceptorexcept*clause), returns the exception instance that was caught by this handler. When exception handlers are nested within one another, only the exception handled by the innermost handler is accessible.

If no exception handler is executing, this function returnsNone.

Added in version 3.11.

sys.exc_info()

This function returns the old-style representation of the handled exception. If an exceptioneis currently handled (so exception()would returne),exc_info()returns the tuple(type(e),e,e.__traceback__). That is, a tuple containing the type of the exception (a subclass of BaseException), the exception itself, and atraceback objectwhich typically encapsulates the call stack at the point where the exception last occurred.

If no exception is being handled anywhere on the stack, this function return a tuple containing threeNonevalues.

Changed in version 3.11:Thetypeandtracebackfields are now derived from thevalue (the exception instance), so when an exception is modified while it is being handled, the changes are reflected in the results of subsequent calls toexc_info().

sys.exec_prefix

A string giving the site-specific directory prefix where the platform-dependent Python files are installed; by default, this is also'/usr/local'.This can be set at build time with the--exec-prefixargument to the configurescript. Specifically, all configuration files (e.g. the pyconfig.hheader file) are installed in the directory exec_prefix/lib/pythonX.Y/config,and shared library modules are installed inexec_prefix/lib/pythonX.Y/lib-dynload,whereX.Y is the version number of Python, for example3.2.

Note

If avirtual environmentis in effect, this value will be changed insite.pyto point to the virtual environment. The value for the Python installation will still be available, via base_exec_prefix.

sys.executable

A string giving the absolute path of the executable binary for the Python interpreter, on systems where this makes sense. If Python is unable to retrieve the real path to its executable,sys.executablewill be an empty string orNone.

sys.exit([arg])

Raise aSystemExitexception, signaling an intention to exit the interpreter.

The optional argumentargcan be an integer giving the exit status (defaulting to zero), or another type of object. If it is an integer, zero is considered “successful termination” and any nonzero value is considered “abnormal termination” by shells and the like. Most systems require it to be in the range 0–127, and produce undefined results otherwise. Some systems have a convention for assigning specific meanings to specific exit codes, but these are generally underdeveloped; Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors. If another type of object is passed,Noneis equivalent to passing zero, and any other object is printed tostderrand results in an exit code of 1. In particular,sys.exit( "someerrormessage ")is a quick way to exit a program when an error occurs.

Sinceexit()ultimately “only” raises an exception, it will only exit the process when called from the main thread, and the exception is not intercepted. Cleanup actions specified by finally clauses oftrystatements are honored, and it is possible to intercept the exit attempt at an outer level.

Changed in version 3.6:If an error occurs in the cleanup after the Python interpreter has caughtSystemExit(such as an error flushing buffered data in the standard streams), the exit status is changed to 120.

sys.flags

Thenamed tupleflagsexposes the status of command line flags. The attributes are read only.

flags.debug	-d
flags.inspect	-i
flags.interactive	-i
flags.isolated	-I
flags.optimize	-Oor-OO
flags.dont_write_bytecode	-B
flags.no_user_site	-s
flags.no_site	-S
flags.ignore_environment	-E
flags.verbose	-v
flags.bytes_warning	-b
flags.quiet	-q
flags.hash_randomization	-R
flags.dev_mode	-Xdev(Python Development Mode)
flags.utf8_mode	-Xutf8
flags.safe_path	-P
flags.int_max_str_digits	-Xint_max_str_digits (integer string conversion length limitation)
flags.warn_default_encoding	-Xwarn_default_encoding

Changed in version 3.2:Addedquietattribute for the new-qflag.

Added in version 3.2.3:Thehash_randomizationattribute.

Changed in version 3.3:Removed obsoletedivision_warningattribute.

Changed in version 3.4:Addedisolatedattribute for-Iisolatedflag.

Changed in version 3.7:Added thedev_modeattribute for the newPython Development Modeand theutf8_modeattribute for the new-X utf8flag.

Changed in version 3.10:Addedwarn_default_encodingattribute for-Xwarn_default_encodingflag.

Changed in version 3.11:Added thesafe_pathattribute for-Poption.

Changed in version 3.11:Added theint_max_str_digitsattribute.

sys.float_info

Anamed tupleholding information about the float type. It contains low level information about the precision and internal representation. The values correspond to the various floating-point constants defined in the standard header filefloat.hfor the ‘C’ programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard [C99],‘Characteristics of floating types’, for details.

Attributes of thefloat_infonamed tuple

attribute	float.h macro	explanation
float_info.epsilon	DBL_EPSILON	difference between 1.0 and the least value greater than 1.0 that is representable as a float. See alsomath.ulp().
float_info.dig	DBL_DIG	The maximum number of decimal digits that can be faithfully represented in a float; see below.
float_info.mant_dig	DBL_MANT_DIG	Float precision: the number of base-radixdigits in the significand of a float.
float_info.max	DBL_MAX	The maximum representable positive finite float.
float_info.max_exp	DBL_MAX_EXP	The maximum integeresuch thatradix**(e-1)is a representable finite float.
float_info.max_10_exp	DBL_MAX_10_EXP	The maximum integeresuch that10**eis in the range of representable finite floats.
float_info.min	DBL_MIN	The minimum representable positivenormalizedfloat. Usemath.ulp(0.0)to get the smallest positive denormalizedrepresentable float.
float_info.min_exp	DBL_MIN_EXP	The minimum integeresuch thatradix**(e-1)is a normalized float.
float_info.min_10_exp	DBL_MIN_10_EXP	The minimum integeresuch that10**eis a normalized float.
float_info.radix	FLT_RADIX	The radix of exponent representation.
float_info.rounds	FLT_ROUNDS	An integer representing the rounding mode for floating-point arithmetic. This reflects the value of the systemFLT_ROUNDSmacro at interpreter startup time: -1:indeterminable 0:toward zero 1:to nearest 2:toward positive infinity 3:toward negative infinity All other values forFLT_ROUNDScharacterize implementation-defined rounding behavior.

The attributesys.float_info.digneeds further explanation. If sis any string representing a decimal number with at most sys.float_info.digsignificant digits, then convertingsto a float and back again will recover a string representing the same decimal value:

>>>importsys
>>>sys.float_info.dig
15
>>>s='3.14159265358979'# decimal string with 15 significant digits
>>>format(float(s),'.15g')# convert to float and back -> same value
'3.14159265358979'

But for strings with more thansys.float_info.digsignificant digits, this isn’t always true:

>>>s='9876543211234567'# 16 significant digits is too many!
>>>format(float(s),'.16g')# conversion changes value
'9876543211234568'

sys.float_repr_style

A string indicating how therepr()function behaves for floats. If the string has value'short'then for a finite floatx,repr(x)aims to produce a short string with the property thatfloat(repr(x))==x.This is the usual behaviour in Python 3.1 and later. Otherwise,float_repr_stylehas value 'legacy'andrepr(x)behaves in the same way as it did in versions of Python prior to 3.1.

Added in version 3.1.

sys.getallocatedblocks()

Return the number of memory blocks currently allocated by the interpreter, regardless of their size. This function is mainly useful for tracking and debugging memory leaks. Because of the interpreter’s internal caches, the result can vary from call to call; you may have to call _clear_type_cache()andgc.collect()to get more predictable results.

If a Python build or implementation cannot reasonably compute this information,getallocatedblocks()is allowed to return 0 instead.

Added in version 3.4.

sys.getunicodeinternedsize()

Return the number of unicode objects that have been interned.

Added in version 3.12.

sys.getandroidapilevel()

Return the build time API version of Android as an integer.

Availability:Android.

Added in version 3.7.

sys.getdefaultencoding()

Return the name of the current default string encoding used by the Unicode implementation.

sys.getdlopenflags()

Return the current value of the flags that are used for dlopen()calls. Symbolic names for the flag values can be found in theosmodule (RTLD_xxxconstants, e.g. os.RTLD_LAZY).

Availability:Unix.

sys.getfilesystemencoding()

Get thefilesystem encoding: the encoding used with thefilesystem error handlerto convert between Unicode filenames and bytes filenames. The filesystem error handler is returned from getfilesystemencodeerrors().

For best compatibility, str should be used for filenames in all cases, although representing filenames as bytes is also supported. Functions accepting or returning filenames should support either str or bytes and internally convert to the system’s preferred representation.

os.fsencode()andos.fsdecode()should be used to ensure that the correct encoding and errors mode are used.

Thefilesystem encoding and error handlerare configured at Python startup by thePyConfig_Read()function: see filesystem_encodingand filesystem_errorsmembers ofPyConfig.

Changed in version 3.2:getfilesystemencoding()result cannot beNoneanymore.

Changed in version 3.6:Windows is no longer guaranteed to return'mbcs'.SeePEP 529 and_enablelegacywindowsfsencoding()for more information.

Changed in version 3.7:Return'utf-8'if thePython UTF-8 Modeis enabled.

sys.getfilesystemencodeerrors()

Get thefilesystem error handler:the error handler used with thefilesystem encodingto convert between Unicode filenames and bytes filenames. The filesystem encoding is returned from getfilesystemencoding().

os.fsencode()andos.fsdecode()should be used to ensure that the correct encoding and errors mode are used.

Thefilesystem encoding and error handlerare configured at Python startup by thePyConfig_Read()function: see filesystem_encodingand filesystem_errorsmembers ofPyConfig.

Added in version 3.6.

sys.get_int_max_str_digits()

Returns the current value for theinteger string conversion length limitation.See alsoset_int_max_str_digits().

Added in version 3.11.

sys.getrefcount(object)

Return the reference count of theobject.The count returned is generally one higher than you might expect, because it includes the (temporary) reference as an argument togetrefcount().

Note that the returned value may not actually reflect how many references to the object are actually held. For example, some objects are “immortal” and have a very high refcount that does not reflect the actual number of references. Consequently, do not rely on the returned value to be accurate, other than a value of 0 or 1.

Changed in version 3.12:Immortal objects have very large refcounts that do not match the actual number of references to the object.

sys.getrecursionlimit()

Return the current value of the recursion limit, the maximum depth of the Python interpreter stack. This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python. It can be set by setrecursionlimit().

sys.getsizeof(object[,default])

Return the size of an object in bytes. The object can be any type of object. All built-in objects will return correct results, but this does not have to hold true for third-party extensions as it is implementation specific.

Only the memory consumption directly attributed to the object is accounted for, not the memory consumption of objects it refers to.

If given,defaultwill be returned if the object does not provide means to retrieve the size. Otherwise aTypeErrorwill be raised.

getsizeof()calls the object’s__sizeof__method and adds an additional garbage collector overhead if the object is managed by the garbage collector.

Seerecursive sizeof recipe for an example of usinggetsizeof()recursively to find the size of containers and all their contents.

sys.getswitchinterval()

Return the interpreter’s “thread switch interval”; see setswitchinterval().

Added in version 3.2.

sys._getframe([depth])

Return a frame object from the call stack. If optional integerdepthis given, return the frame object that many calls below the top of the stack. If that is deeper than the call stack,ValueErroris raised. The default fordepthis zero, returning the frame at the top of the call stack.

Raises anauditing eventsys._getframewith argumentframe.

CPython implementation detail:This function should be used for internal and specialized purposes only. It is not guaranteed to exist in all implementations of Python.

sys._getframemodulename([depth])

Return the name of a module from the call stack. If optional integerdepth is given, return the module that many calls below the top of the stack. If that is deeper than the call stack, or if the module is unidentifiable, Noneis returned. The default fordepthis zero, returning the module at the top of the call stack.

Raises anauditing eventsys._getframemodulenamewith argumentdepth.

CPython implementation detail:This function should be used for internal and specialized purposes only. It is not guaranteed to exist in all implementations of Python.

sys.getprofile()

Get the profiler function as set bysetprofile().

sys.gettrace()

Get the trace function as set bysettrace().

CPython implementation detail:Thegettrace()function is intended only for implementing debuggers, profilers, coverage tools and the like. Its behavior is part of the implementation platform, rather than part of the language definition, and thus may not be available in all Python implementations.

sys.getwindowsversion()

Return a named tuple describing the Windows version currently running. The named elements aremajor,minor, build,platform,service_pack,service_pack_minor, service_pack_major,suite_mask,product_typeand platform_version.service_packcontains a string, platform_versiona 3-tuple and all other values are integers. The components can also be accessed by name, so sys.getwindowsversion()[0]is equivalent to sys.getwindowsversion().major.For compatibility with prior versions, only the first 5 elements are retrievable by indexing.

platformwill be2(VER_PLATFORM_WIN32_NT).

product_typemay be one of the following values:

Constant	Meaning
1(VER_NT_WORKSTATION)	The system is a workstation.
2(VER_NT_DOMAIN_CONTROLLER)	The system is a domain controller.
3(VER_NT_SERVER)	The system is a server, but not a domain controller.

This function wraps the Win32GetVersionEx()function; see the Microsoft documentation onOSVERSIONINFOEX()for more information about these fields.

platform_versionreturns the major version, minor version and build number of the current operating system, rather than the version that is being emulated for the process. It is intended for use in logging rather than for feature detection.

Note

platform_versionderives the version from kernel32.dll which can be of a different version than the OS version. Please useplatformmodule for achieving accurate OS version.

Availability:Windows.

Changed in version 3.2:Changed to a named tuple and addedservice_pack_minor, service_pack_major,suite_mask,andproduct_type.

Changed in version 3.6:Addedplatform_version

sys.get_asyncgen_hooks()

Returns anasyncgen_hooksobject, which is similar to a namedtupleof the form(firstiter,finalizer), wherefirstiterandfinalizerare expected to be eitherNoneor functions which take anasynchronous generator iteratoras an argument, and are used to schedule finalization of an asynchronous generator by an event loop.

Added in version 3.6:SeePEP 525for more details.

Note

This function has been added on a provisional basis (seePEP 411 for details.)

sys.get_coroutine_origin_tracking_depth()

Get the current coroutine origin tracking depth, as set by set_coroutine_origin_tracking_depth().

Added in version 3.7.

Note

This function has been added on a provisional basis (seePEP 411 for details.) Use it only for debugging purposes.

sys.hash_info

Anamed tuplegiving parameters of the numeric hash implementation. For more details about hashing of numeric types, see Hashing of numeric types.

hash_info.width

The width in bits used for hash values

hash_info.modulus

The prime modulus P used for numeric hash scheme

hash_info.inf

The hash value returned for a positive infinity

hash_info.nan

(This attribute is no longer used)

hash_info.imag

The multiplier used for the imaginary part of a complex number

hash_info.algorithm

The name of the algorithm for hashing of str, bytes, and memoryview

hash_info.hash_bits

The internal output size of the hash algorithm

hash_info.seed_bits

The size of the seed key of the hash algorithm

Added in version 3.2.

Changed in version 3.4:Addedalgorithm,hash_bitsandseed_bits

sys.hexversion

The version number encoded as a single integer. This is guaranteed to increase with each version, including proper support for non-production releases. For example, to test that the Python interpreter is at least version 1.5.2, use:

ifsys.hexversion>=0x010502F0:
# use some advanced feature
...
else:
# use an alternative implementation or warn the user
...

This is calledhexversionsince it only really looks meaningful when viewed as the result of passing it to the built-inhex()function. The named tuplesys.version_infomay be used for a more human-friendly encoding of the same information.

More details ofhexversioncan be found atAPI and ABI Versioning.

sys.implementation

An object containing information about the implementation of the currently running Python interpreter. The following attributes are required to exist in all Python implementations.

nameis the implementation’s identifier, e.g.'cpython'.The actual string is defined by the Python implementation, but it is guaranteed to be lower case.

versionis a named tuple, in the same format as sys.version_info.It represents the version of the Python implementation.This has a distinct meaning from the specific version of the Pythonlanguageto which the currently running interpreter conforms, whichsys.version_inforepresents. For example, for PyPy 1.8sys.implementation.versionmight be sys.version_info(1,8,0,'final',0),whereassys.version_info would besys.version_info(2,7,2,'final',0).For CPython they are the same value, since it is the reference implementation.

hexversionis the implementation version in hexadecimal format, like sys.hexversion.

cache_tagis the tag used by the import machinery in the filenames of cached modules. By convention, it would be a composite of the implementation’s name and version, like'cpython-33'.However, a Python implementation may use some other value if appropriate. If cache_tagis set toNone,it indicates that module caching should be disabled.

sys.implementationmay contain additional attributes specific to the Python implementation. These non-standard attributes must start with an underscore, and are not described here. Regardless of its contents, sys.implementationwill not change during a run of the interpreter, nor between implementation versions. (It may change between Python language versions, however.) SeePEP 421for more information.

Added in version 3.3.

Note

The addition of new required attributes must go through the normal PEP process. SeePEP 421for more information.

sys.int_info

Anamed tuplethat holds information about Python’s internal representation of integers. The attributes are read only.

int_info.bits_per_digit

The number of bits held in each digit. Python integers are stored internally in base2**int_info.bits_per_digit.

int_info.sizeof_digit

The size in bytes of the C type used to represent a digit.

int_info.default_max_str_digits

The default value forsys.get_int_max_str_digits() when it is not otherwise explicitly configured.

int_info.str_digits_check_threshold

The minimum non-zero value forsys.set_int_max_str_digits(), PYTHONINTMAXSTRDIGITS,or-Xint_max_str_digits.

Added in version 3.1.

Changed in version 3.11:Addeddefault_max_str_digitsand str_digits_check_threshold.

sys.__interactivehook__

When this attribute exists, its value is automatically called (with no arguments) when the interpreter is launched ininteractive mode.This is done after thePYTHONSTARTUPfile is read, so that you can set this hook there. Thesitemodule sets this.

Raises anauditing event cpython.run_interactivehookwith the hook object as the argument when the hook is called on startup.

Added in version 3.4.

sys.intern(string)

Enterstringin the table of “interned” strings and return the interned string – which isstringitself or a copy. Interning strings is useful to gain a little performance on dictionary lookup – if the keys in a dictionary are interned, and the lookup key is interned, the key comparisons (after hashing) can be done by a pointer compare instead of a string compare. Normally, the names used in Python programs are automatically interned, and the dictionaries used to hold module, class or instance attributes have interned keys.

Interned strings are not immortal; you must keep a reference to the return value ofintern()around to benefit from it.

sys.is_finalizing()

ReturnTrueif the Python interpreter is shutting down,Falseotherwise.

Added in version 3.5.

sys.last_exc

This variable is not always defined; it is set to the exception instance when an exception is not handled and the interpreter prints an error message and a stack traceback. Its intended use is to allow an interactive user to import a debugger module and engage in post-mortem debugging without having to re-execute the command that caused the error. (Typical use is importpdb;pdb.pm()to enter the post-mortem debugger; seepdb module for more information.)

Added in version 3.12.

sys.last_type

sys.last_value

sys.last_traceback

These three variables are deprecated; usesys.last_excinstead. They hold the legacy representation ofsys.last_exc,as returned fromexc_info()above.

sys.maxsize

An integer giving the maximum value a variable of typePy_ssize_tcan take. It’s usually2**31-1on a 32-bit platform and2**63-1on a 64-bit platform.

sys.maxunicode

An integer giving the value of the largest Unicode code point, i.e.1114111(0x10FFFFin hexadecimal).

Changed in version 3.3:BeforePEP 393,sys.maxunicodeused to be either0xFFFF or0x10FFFF,depending on the configuration option that specified whether Unicode characters were stored as UCS-2 or UCS-4.

sys.meta_path

A list ofmeta path finderobjects that have their find_spec()methods called to see if one of the objects can find the module to be imported. By default, it holds entries that implement Python’s default import semantics. The find_spec()method is called with at least the absolute name of the module being imported. If the module to be imported is contained in a package, then the parent package’s__path__ attribute is passed in as a second argument. The method returns a module spec,orNoneif the module cannot be found.

See also

importlib.abc.MetaPathFinder

The abstract base class defining the interface of finder objects on meta_path.

importlib.machinery.ModuleSpec

The concrete class which find_spec()should return instances of.

Changed in version 3.4:Module specswere introduced in Python 3.4, by PEP 451.

Changed in version 3.12:Removed the fallback that looked for afind_module()method if ameta_pathentry didn’t have a find_spec()method.

sys.modules

This is a dictionary that maps module names to modules which have already been loaded. This can be manipulated to force reloading of modules and other tricks. However, replacing the dictionary will not necessarily work as expected and deleting essential items from the dictionary may cause Python to fail. If you want to iterate over this global dictionary always use sys.modules.copy()ortuple(sys.modules)to avoid exceptions as its size may change during iteration as a side effect of code or activity in other threads.

sys.orig_argv

The list of the original command line arguments passed to the Python executable.

The elements ofsys.orig_argvare the arguments to the Python interpreter, while the elements ofsys.argvare the arguments to the user’s program. Arguments consumed by the interpreter itself will be present insys.orig_argv and missing fromsys.argv.

Added in version 3.10.

sys.path

A list of strings that specifies the search path for modules. Initialized from the environment variablePYTHONPATH,plus an installation-dependent default.

By default, as initialized upon program startup, a potentially unsafe path is prepended tosys.path(beforethe entries inserted as a result ofPYTHONPATH):

• python-mmodulecommand line: prepend the current working directory.

• pythonscript.pycommand line: prepend the script’s directory. If it’s a symbolic link, resolve symbolic links.

• python-ccodeandpython(REPL) command lines: prepend an empty string, which means the current working directory.

To not prepend this potentially unsafe path, use the-Pcommand line option or thePYTHONSAFEPATHenvironment variable.

A program is free to modify this list for its own purposes. Only strings should be added tosys.path;all other data types are ignored during import.

See also

• ModulesiteThis describes how to use.pth files to extendsys.path.

sys.path_hooks

A list of callables that take a path argument to try to create a finderfor the path. If a finder can be created, it is to be returned by the callable, else raiseImportError.

Originally specified inPEP 302.

sys.path_importer_cache

A dictionary acting as a cache forfinderobjects. The keys are paths that have been passed tosys.path_hooksand the values are the finders that are found. If a path is a valid file system path but no finder is found onsys.path_hooksthenNoneis stored.

Originally specified inPEP 302.

sys.platform

This string contains a platform identifier that can be used to append platform-specific components tosys.path,for instance.

For Unix systems, except on Linux and AIX, this is the lowercased OS name as returned byuname-swith the first part of the version as returned by uname-rappended, e.g.'sunos5'or'freebsd8',at the time when Python was built.Unless you want to test for a specific system version, it is therefore recommended to use the following idiom:

ifsys.platform.startswith('freebsd'):
# FreeBSD-specific code here...
elifsys.platform.startswith('linux'):
# Linux-specific code here...
elifsys.platform.startswith('aix'):
# AIX-specific code here...

For other systems, the values are:

System	platformvalue
AIX	'aix'
Emscripten	'emscripten'
Linux	'linux'
WASI	'wasi'
Windows	'win32'
Windows/Cygwin	'cygwin'
macOS	'darwin'

Changed in version 3.3:On Linux,sys.platformdoesn’t contain the major version anymore. It is always'linux',instead of'linux2'or'linux3'.Since older Python versions include the version number, it is recommended to always use thestartswithidiom presented above.

Changed in version 3.8:On AIX,sys.platformdoesn’t contain the major version anymore. It is always'aix',instead of'aix5'or'aix7'.Since older Python versions include the version number, it is recommended to always use thestartswithidiom presented above.

See also

os.namehas a coarser granularity.os.uname()gives system-dependent version information.

Theplatformmodule provides detailed checks for the system’s identity.

sys.platlibdir

Name of the platform-specific library directory. It is used to build the path of standard library and the paths of installed extension modules.

It is equal to"lib"on most platforms. On Fedora and SuSE, it is equal to"lib64"on 64-bit platforms which gives the followingsys.path paths (whereX.Yis the Pythonmajor.minorversion):

• /usr/lib64/pythonX.Y/: Standard library (likeos.pyof theosmodule)

• /usr/lib64/pythonX.Y/lib-dynload/: C extension modules of the standard library (like theerrnomodule, the exact filename is platform specific)

• /usr/lib/pythonX.Y/site-packages/(always uselib,not sys.platlibdir): Third-party modules

• /usr/lib64/pythonX.Y/site-packages/: C extension modules of third-party packages

Added in version 3.9.

sys.prefix

A string giving the site-specific directory prefix where the platform independent Python files are installed; on Unix, the default is /usr/local.This can be set at build time with the--prefix argument to theconfigurescript. See Installation pathsfor derived paths.

Note

If avirtual environmentis in effect, this value will be changed insite.pyto point to the virtual environment. The value for the Python installation will still be available, viabase_prefix.

sys.ps1

sys.ps2

Strings specifying the primary and secondary prompt of the interpreter. These are only defined if the interpreter is in interactive mode. Their initial values in this case are'>>>'and'...'.If a non-string object is assigned to either variable, itsstr()is re-evaluated each time the interpreter prepares to read a new interactive command; this can be used to implement a dynamic prompt.

sys.setdlopenflags(n)

Set the flags used by the interpreter fordlopen()calls, such as when the interpreter loads extension modules. Among other things, this will enable a lazy resolving of symbols when importing a module, if called as sys.setdlopenflags(0).To share symbols across extension modules, call as sys.setdlopenflags(os.RTLD_GLOBAL).Symbolic names for the flag values can be found in theosmodule (RTLD_xxxconstants, e.g. os.RTLD_LAZY).

Availability:Unix.

sys.set_int_max_str_digits(maxdigits)

Set theinteger string conversion length limitationused by this interpreter. See also get_int_max_str_digits().

Added in version 3.11.

sys.setprofile(profilefunc)

Set the system’s profile function, which allows you to implement a Python source code profiler in Python. See chapterThe Python Profilersfor more information on the Python profiler. The system’s profile function is called similarly to the system’s trace function (seesettrace()), but it is called with different events, for example it isn’t called for each executed line of code (only on call and return, but the return event is reported even when an exception has been set). The function is thread-specific, but there is no way for the profiler to know about context switches between threads, so it does not make sense to use this in the presence of multiple threads. Also, its return value is not used, so it can simply returnNone.Error in the profile function will cause itself unset.

Note

The same tracing mechanism is used forsetprofile()assettrace(). To trace calls withsetprofile()inside a tracing function (e.g. in a debugger breakpoint), seecall_tracing().

Profile functions should have three arguments:frame,event,and arg.frameis the current stack frame.eventis a string:'call', 'return','c_call','c_return',or'c_exception'.argdepends on the event type.

The events have the following meaning:

'call'

A function is called (or some other code block entered). The profile function is called;argisNone.

'return'

A function (or other code block) is about to return. The profile function is called;argis the value that will be returned, orNone if the event is caused by an exception being raised.

'c_call'

A C function is about to be called. This may be an extension function or a built-in.argis the C function object.

'c_return'

A C function has returned.argis the C function object.

'c_exception'

A C function has raised an exception.argis the C function object.

Raises anauditing eventsys.setprofilewith no arguments.

sys.setrecursionlimit(limit)

Set the maximum depth of the Python interpreter stack tolimit.This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python.

The highest possible limit is platform-dependent. A user may need to set the limit higher when they have a program that requires deep recursion and a platform that supports a higher limit. This should be done with care, because a too-high limit can lead to a crash.

If the new limit is too low at the current recursion depth, a RecursionErrorexception is raised.

Changed in version 3.5.1:ARecursionErrorexception is now raised if the new limit is too low at the current recursion depth.

sys.setswitchinterval(interval)

Set the interpreter’s thread switch interval (in seconds). This floating-point value determines the ideal duration of the “timeslices” allocated to concurrently running Python threads. Please note that the actual value can be higher, especially if long-running internal functions or methods are used. Also, which thread becomes scheduled at the end of the interval is the operating system’s decision. The interpreter doesn’t have its own scheduler.

Added in version 3.2.

sys.settrace(tracefunc)

Set the system’s trace function, which allows you to implement a Python source code debugger in Python. The function is thread-specific; for a debugger to support multiple threads, it must register a trace function using settrace()for each thread being debugged or usethreading.settrace().

Trace functions should have three arguments:frame,event,and arg.frameis the current stack frame.eventis a string:'call', 'line','return','exception'or'opcode'.argdepends on the event type.

The trace function is invoked (witheventset to'call') whenever a new local scope is entered; it should return a reference to a local trace function to be used for the new scope, orNoneif the scope shouldn’t be traced.

The local trace function should return a reference to itself, or to another function which would then be used as the local trace function for the scope.

If there is any error occurred in the trace function, it will be unset, just likesettrace(None)is called.

Note

Tracing is disabled while calling the trace function (e.g. a function set by settrace()). For recursive tracing seecall_tracing().

The events have the following meaning:

'call'

A function is called (or some other code block entered). The global trace function is called;argisNone;the return value specifies the local trace function.

'line'

The interpreter is about to execute a new line of code or re-execute the condition of a loop. The local trace function is called;argis None;the return value specifies the new local trace function. See Objects/lnotab_notes.txtfor a detailed explanation of how this works. Per-line events may be disabled for a frame by setting f_trace_linestoFalseon that frame.

'return'

A function (or other code block) is about to return. The local trace function is called;argis the value that will be returned, orNone if the event is caused by an exception being raised. The trace function’s return value is ignored.

'exception'

An exception has occurred. The local trace function is called;argis a tuple(exception,value,traceback);the return value specifies the new local trace function.

'opcode'

The interpreter is about to execute a new opcode (seedisfor opcode details). The local trace function is called;argis None;the return value specifies the new local trace function. Per-opcode events are not emitted by default: they must be explicitly requested by settingf_trace_opcodestoTrueon the frame.

Note that as an exception is propagated down the chain of callers, an 'exception'event is generated at each level.

For more fine-grained usage, it’s possible to set a trace function by assigningframe.f_trace=tracefuncexplicitly, rather than relying on it being set indirectly via the return value from an already installed trace function. This is also required for activating the trace function on the current frame, whichsettrace()doesn’t do. Note that in order for this to work, a global tracing function must have been installed withsettrace()in order to enable the runtime tracing machinery, but it doesn’t need to be the same tracing function (e.g. it could be a low overhead tracing function that simply returnsNoneto disable itself immediately on each frame).

For more information on code and frame objects, refer toThe standard type hierarchy.

Raises anauditing eventsys.settracewith no arguments.

CPython implementation detail:Thesettrace()function is intended only for implementing debuggers, profilers, coverage tools and the like. Its behavior is part of the implementation platform, rather than part of the language definition, and thus may not be available in all Python implementations.

Changed in version 3.7:'opcode'event type added;f_trace_linesand f_trace_opcodesattributes added to frames

Changed in version 3.12:'opcode'event will only be emitted iff_trace_opcodes of at least one frame has been set toTruebeforesettrace() is called. This behavior will be changed back in 3.13 to be consistent with previous versions.

sys.set_asyncgen_hooks([firstiter][,finalizer])

Accepts two optional keyword arguments which are callables that accept an asynchronous generator iteratoras an argument. Thefirstiter callable will be called when an asynchronous generator is iterated for the first time. Thefinalizerwill be called when an asynchronous generator is about to be garbage collected.

Raises anauditing eventsys.set_asyncgen_hooks_firstiterwith no arguments.

Raises anauditing eventsys.set_asyncgen_hooks_finalizerwith no arguments.

Two auditing events are raised because the underlying API consists of two calls, each of which must raise its own event.

Added in version 3.6:SeePEP 525for more details, and for a reference example of a finalizermethod see the implementation of asyncio.Loop.shutdown_asyncgensin Lib/asyncio/base_events.py

Note

This function has been added on a provisional basis (seePEP 411 for details.)

sys.set_coroutine_origin_tracking_depth(depth)

Allows enabling or disabling coroutine origin tracking. When enabled, thecr_originattribute on coroutine objects will contain a tuple of (filename, line number, function name) tuples describing the traceback where the coroutine object was created, with the most recent call first. When disabled,cr_originwill beNone.

To enable, pass adepthvalue greater than zero; this sets the number of frames whose information will be captured. To disable, pass setdepthto zero.

This setting is thread-specific.

Added in version 3.7.

Note

This function has been added on a provisional basis (seePEP 411 for details.) Use it only for debugging purposes.

sys.activate_stack_trampoline(backend,/)

Activate the stack profiler trampolinebackend. The only supported backend is"perf".

Availability:Linux.

Added in version 3.12.

See also

• Python support for the Linux perf profiler

• https://perf.wiki.kernel.org

sys.deactivate_stack_trampoline()

Deactivate the current stack profiler trampoline backend.

If no stack profiler is activated, this function has no effect.

Availability:Linux.

Added in version 3.12.

sys.is_stack_trampoline_active()

ReturnTrueif a stack profiler trampoline is active.

Availability:Linux.

Added in version 3.12.

sys._enablelegacywindowsfsencoding()

Changes thefilesystem encoding and error handlerto ‘mbcs’ and ‘replace’ respectively, for consistency with versions of Python prior to 3.6.

This is equivalent to defining thePYTHONLEGACYWINDOWSFSENCODING environment variable before launching Python.

See alsosys.getfilesystemencoding()and sys.getfilesystemencodeerrors().

Availability:Windows.

Added in version 3.6:SeePEP 529for more details.

sys.stdin

sys.stdout

sys.stderr

File objectsused by the interpreter for standard input, output and errors:

• stdinis used for all interactive input (including calls to input());

• stdoutis used for the output ofprint()andexpression statements and for the prompts ofinput();

• The interpreter’s own prompts and its error messages go tostderr.

These streams are regulartext fileslike those returned by theopen()function. Their parameters are chosen as follows:

• The encoding and error handling are is initialized from PyConfig.stdio_encodingandPyConfig.stdio_errors.

  On Windows, UTF-8 is used for the console device. Non-character devices such as disk files and pipes use the system locale encoding (i.e. the ANSI codepage). Non-console character devices such as NUL (i.e. whereisatty()returnsTrue) use the value of the console input and output codepages at startup, respectively for stdin and stdout/stderr. This defaults to the systemlocale encodingif the process is not initially attached to a console.

  The special behaviour of the console can be overridden by setting the environment variable PYTHONLEGACYWINDOWSSTDIO before starting Python. In that case, the console codepages are used as for any other character device.

  Under all platforms, you can override the character encoding by setting thePYTHONIOENCODINGenvironment variable before starting Python or by using the new-Xutf8command line option andPYTHONUTF8environment variable. However, for the Windows console, this only applies when PYTHONLEGACYWINDOWSSTDIOis also set.

• When interactive, thestdoutstream is line-buffered. Otherwise, it is block-buffered like regular text files. Thestderrstream is line-buffered in both cases. You can make both streams unbuffered by passing the-ucommand-line option or setting the PYTHONUNBUFFEREDenvironment variable.

Changed in version 3.9:Non-interactivestderris now line-buffered instead of fully buffered.

Note

To write or read binary data from/to the standard streams, use the underlying binarybufferobject. For example, to write bytes tostdout,usesys.stdout.buffer.write(b'abc').

However, if you are writing a library (and do not control in which context its code will be executed), be aware that the standard streams may be replaced with file-like objects likeio.StringIOwhich do not support thebufferattribute.

sys.__stdin__

sys.__stdout__

sys.__stderr__

These objects contain the original values ofstdin,stderrand stdoutat the start of the program. They are used during finalization, and could be useful to print to the actual standard stream no matter if the sys.std*object has been redirected.

It can also be used to restore the actual files to known working file objects in case they have been overwritten with a broken object. However, the preferred way to do this is to explicitly save the previous stream before replacing it, and restore the saved object.

Note

Under some conditionsstdin,stdoutandstderras well as the original values__stdin__,__stdout__and__stderr__can be None.It is usually the case for Windows GUI apps that aren’t connected to a console and Python apps started withpythonw.

sys.stdlib_module_names

A frozenset of strings containing the names of standard library modules.

It is the same on all platforms. Modules which are not available on some platforms and modules disabled at Python build are also listed. All module kinds are listed: pure Python, built-in, frozen and extension modules. Test modules are excluded.

For packages, only the main package is listed: sub-packages and sub-modules are not listed. For example, theemailpackage is listed, but the email.mimesub-package and theemail.messagesub-module are not listed.

See also thesys.builtin_module_nameslist.

Added in version 3.10.

sys.thread_info

Anamed tupleholding information about the thread implementation.

thread_info.name

The name of the thread implementation:

• "nt":Windows threads

• "pthread":POSIX threads

• "pthread-stubs":stub POSIX threads (on WebAssembly platforms without threading support)

• "solaris":Solaris threads

thread_info.lock

The name of the lock implementation:

• "semaphore":a lock uses a semaphore

• "mutex+cond":a lock uses a mutex and a condition variable

• Noneif this information is unknown

thread_info.version

The name and version of the thread library. It is a string, orNoneif this information is unknown.

Added in version 3.3.

sys.tracebacklimit

When this variable is set to an integer value, it determines the maximum number of levels of traceback information printed when an unhandled exception occurs. The default is1000.When set to0or less, all traceback information is suppressed and only the exception type and value are printed.

sys.unraisablehook(unraisable,/)

Handle an unraisable exception.

Called when an exception has occurred but there is no way for Python to handle it. For example, when a destructor raises an exception or during garbage collection (gc.collect()).

Theunraisableargument has the following attributes:

• exc_type:Exception type.

• exc_value:Exception value, can beNone.

• exc_traceback:Exception traceback, can beNone.

• err_msg:Error message, can beNone.

• object:Object causing the exception, can beNone.

The default hook formatserr_msgandobjectas: f'{err_msg}:{object!r}';use “Exception ignored in” error message iferr_msgisNone.

sys.unraisablehook()can be overridden to control how unraisable exceptions are handled.

See also

excepthook()which handles uncaught exceptions.

Warning

Storingexc_valueusing a custom hook can create a reference cycle. It should be cleared explicitly to break the reference cycle when the exception is no longer needed.

Storingobjectusing a custom hook can resurrect it if it is set to an object which is being finalized. Avoid storingobjectafter the custom hook completes to avoid resurrecting objects.

Raise an auditing eventsys.unraisablehookwith arguments hook,unraisablewhen an exception that cannot be handled occurs. Theunraisableobject is the same as what will be passed to the hook. If no hook has been set,hookmay beNone.

Added in version 3.8.

sys.version

A string containing the version number of the Python interpreter plus additional information on the build number and compiler used. This string is displayed when the interactive interpreter is started. Do not extract version information out of it, rather, useversion_infoand the functions provided by the platformmodule.

sys.api_version

The C API version for this interpreter. Programmers may find this useful when debugging version conflicts between Python and extension modules.

sys.version_info

A tuple containing the five components of the version number:major,minor, micro,releaselevel,andserial.All values exceptreleaselevelare integers; the release level is'alpha','beta','candidate',or 'final'.Theversion_infovalue corresponding to the Python version 2.0 is(2,0,0,'final',0).The components can also be accessed by name, sosys.version_info[0]is equivalent tosys.version_info.major and so on.

Changed in version 3.1:Added named component attributes.

sys.warnoptions

This is an implementation detail of the warnings framework; do not modify this value. Refer to thewarningsmodule for more information on the warnings framework.

sys.winver

The version number used to form registry keys on Windows platforms. This is stored as string resource 1000 in the Python DLL. The value is normally the major and minor versions of the running Python interpreter. It is provided in thesys module for informational purposes; modifying this value has no effect on the registry keys used by Python.

Availability:Windows.

sys.monitoring

Namespace containing functions and constants for register callbacks and controlling monitoring events. Seesys.monitoringfor details.

sys._xoptions

A dictionary of the various implementation-specific flags passed through the-Xcommand-line option. Option names are either mapped to their values, if given explicitly, or toTrue.Example:

$./python-Xa=b-Xc
Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys._xoptions
{'a': 'b', 'c': True}

CPython implementation detail:This is a CPython-specific way of accessing options passed through -X.Other implementations may export them through other means, or not at all.

Added in version 3.2.

Citations

[C99]

ISO/IEC 9899:1999. “Programming languages – C.” A public draft of this standard is available athttps://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf.