Before Python Initialization¶

In an application embedding Python, thePy_Initialize() function mustbe called before using any other Python/C API functions; with the exception ofa few functions and theglobal configuration variables.

The following functions can be safely called before Python is initialized:

• Configuration functions:

  • PyImport_AppendInittab()

  • PyImport_ExtendInittab()

  • PyInitFrozenExtensions()

  • PyMem_SetAllocator()

  • PyMem_SetupDebugHooks()

  • PyObject_SetArenaAllocator()

  • Py_SetPath()

  • Py_SetProgramName()

  • Py_SetPythonHome()

  • Py_SetStandardStreamEncoding()

  • PySys_AddWarnOption()

  • PySys_AddXOption()

  • PySys_ResetWarnOptions()

• Informative functions:

  • Py_IsInitialized()

  • PyMem_GetAllocator()

  • PyObject_GetArenaAllocator()

  • Py_GetBuildInfo()

  • Py_GetCompiler()

  • Py_GetCopyright()

  • Py_GetPlatform()

  • Py_GetVersion()

• Utilities:

  • Py_DecodeLocale()

• Memory allocators:

  • PyMem_RawMalloc()

  • PyMem_RawRealloc()

  • PyMem_RawCalloc()

  • PyMem_RawFree()

Global configuration variables¶

Python has variables for the global configuration to control different featuresand options. By default, these flags are controlled bycommand lineoptions.

When a flag is set by an option, the value of the flag is the number of timesthat the option was set. For example,-b setsPy_BytesWarningFlagto 1 and-bb setsPy_BytesWarningFlag to 2.

intPy_BytesWarningFlag¶

Issue a warning when comparingbytes orbytearray withstr orbytes withint. Issue an error if greateror equal to2.

Set by the-b option.

intPy_DebugFlag¶

Turn on parser debugging output (for expert only, depending on compilationoptions).

Set by the-d option and thePYTHONDEBUG environmentvariable.

intPy_DontWriteBytecodeFlag¶

If set to non-zero, Python won’t try to write.pyc files on theimport of source modules.

Set by the-B option and thePYTHONDONTWRITEBYTECODEenvironment variable.

intPy_FrozenFlag¶

Suppress error messages when calculating the module search path inPy_GetPath().

Private flag used by_freeze_importlib andfrozenmain programs.

intPy_HashRandomizationFlag¶

Set to1 if thePYTHONHASHSEED environment variable is set toa non-empty string.

If the flag is non-zero, read thePYTHONHASHSEED environmentvariable to initialize the secret hash seed.

intPy_IgnoreEnvironmentFlag¶

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

Set by the-E and-I options.

intPy_InspectFlag¶

When a script is passed as first argument or the-c option is used,enter interactive mode after executing the script or the command, even whensys.stdin does not appear to be a terminal.

Set by the-i option and thePYTHONINSPECT environmentvariable.

intPy_InteractiveFlag¶

Set by the-i option.

intPy_IsolatedFlag¶

Run Python in isolated mode. In isolated modesys.path containsneither the script’s directory nor the user’s site-packages directory.

Set by the-I option.

New in version 3.4.

intPy_LegacyWindowsFSEncodingFlag¶

If the flag is non-zero, use thembcs encoding instead of the UTF-8encoding for the filesystem encoding.

Set to1 if thePYTHONLEGACYWINDOWSFSENCODING environmentvariable is set to a non-empty string.

SeePEP 529 for more details.

Availability: Windows.

intPy_LegacyWindowsStdioFlag¶

If the flag is non-zero, useio.FileIO instead ofWindowsConsoleIO forsys standard streams.

Set to1 if thePYTHONLEGACYWINDOWSSTDIO environmentvariable is set to a non-empty string.

SeePEP 528 for more details.

Availability: Windows.

intPy_NoSiteFlag¶

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).

Set by the-S option.

intPy_NoUserSiteDirectory¶

Don’t add theusersite-packagesdirectory tosys.path.

Set by the-s and-I options, and thePYTHONNOUSERSITE environment variable.

intPy_OptimizeFlag¶

Set by the-O option and thePYTHONOPTIMIZE environmentvariable.

intPy_QuietFlag¶

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

Set by the-q option.

New in version 3.2.

intPy_UnbufferedStdioFlag¶

Force the stdout and stderr streams to be unbuffered.

Set by the-u option and thePYTHONUNBUFFEREDenvironment variable.

intPy_VerboseFlag¶

Print a message each time a module is initialized, showing the place(filename or built-in module) from which it is loaded. If greater or equalto2, print a message for each file that is checked for whensearching for a module. Also provides information on module cleanup at exit.

Set by the-v option and thePYTHONVERBOSE environmentvariable.

Initializing and finalizing the interpreter¶

voidPy_Initialize()¶

Initialize the Python interpreter. In an application embedding Python,this should be called before using any other Python/C API functions; seeBefore Python Initialization for the few exceptions.

This initializesthe table of loaded modules (sys.modules), and creates the fundamentalmodulesbuiltins,__main__ andsys. It also initializesthe module search path (sys.path). It does not setsys.argv; usePySys_SetArgvEx() for that. This is a no-op when called for a second time(without callingPy_FinalizeEx() first). There is no return value; it is afatal error if the initialization fails.

Note

On Windows, changes the console mode fromO_TEXT toO_BINARY, which willalso affect non-Python uses of the console using the C Runtime.

voidPy_InitializeEx(int initsigs)¶

This function works likePy_Initialize() ifinitsigs is1. Ifinitsigs is0, it skips initialization registration of signal handlers, whichmight be useful when Python is embedded.

intPy_IsInitialized()¶

Return true (nonzero) when the Python interpreter has been initialized, false(zero) if not. AfterPy_FinalizeEx() is called, this returns false untilPy_Initialize() is called again.

intPy_FinalizeEx()¶

Undo all initializations made byPy_Initialize() and subsequent use ofPython/C API functions, and destroy all sub-interpreters (seePy_NewInterpreter() below) that were created and not yet destroyed sincethe last call toPy_Initialize(). Ideally, this frees all memoryallocated by the Python interpreter. This is a no-op when called for a secondtime (without callingPy_Initialize() again first). Normally thereturn value is0. If there were errors during finalization(flushing buffered data),-1 is returned.

This function is provided for a number of reasons. An embedding applicationmight want to restart Python without having to restart the application itself.An application that has loaded the Python interpreter from a dynamicallyloadable library (or DLL) might want to free all memory allocated by Pythonbefore unloading the DLL. During a hunt for memory leaks in an application adeveloper might want to free all memory allocated by Python before exiting fromthe application.

Bugs and caveats: The destruction of modules and objects in modules is donein random order; this may cause destructors (__del__() methods) to failwhen they depend on other objects (even functions) or modules. Dynamicallyloaded extension modules loaded by Python are not unloaded. Small amounts ofmemory allocated by the Python interpreter may not be freed (if you find a leak,please report it). Memory tied up in circular references between objects is notfreed. Some memory allocated by extension modules may not be freed. Someextensions may not work properly if their initialization routine is called morethan once; this can happen if an application callsPy_Initialize() andPy_FinalizeEx() more than once.

Raises anauditing eventcpython._PySys_ClearAuditHooks with no arguments.

New in version 3.6.

voidPy_Finalize()¶

This is a backwards-compatible version ofPy_FinalizeEx() thatdisregards the return value.

Process-wide parameters¶

intPy_SetStandardStreamEncoding(const char *encoding, const char *errors)¶

This function should be called beforePy_Initialize(), if it iscalled at all. It specifies which encoding and error handling to usewith standard IO, with the same meanings as instr.encode().

It overridesPYTHONIOENCODING values, and allows embedding codeto control IO encoding when the environment variable does not work.

encoding and/orerrors may beNULL to usePYTHONIOENCODING and/or default values (depending on othersettings).

Note thatsys.stderr always uses the “backslashreplace” errorhandler, regardless of this (or any other) setting.

IfPy_FinalizeEx() is called, this function will need to be calledagain in order to affect subsequent calls toPy_Initialize().

Returns0 if successful, a nonzero value on error (e.g. calling after theinterpreter has already been initialized).

New in version 3.4.

voidPy_SetProgramName(const wchar_t *name)¶

This function should be called beforePy_Initialize() is called forthe first time, if it is called at all. It tells the interpreter the valueof theargv[0] argument to themain() function of the program(converted to wide characters).This is used byPy_GetPath() and some other functions below to findthe Python run-time libraries relative to the interpreter executable. Thedefault value is'python'. The argument should point to azero-terminated wide character string in static storage whose contents will notchange for the duration of the program’s execution. No code in the Pythoninterpreter will change the contents of this storage.

UsePy_DecodeLocale() to decode a bytes string to get awchar_* string.

wchar*Py_GetProgramName()¶

Return the program name set withPy_SetProgramName(), or the default.The returned string points into static storage; the caller should not modify itsvalue.

wchar_t*Py_GetPrefix()¶

Return theprefix for installed platform-independent files. This is derivedthrough a number of complicated rules from the program name set withPy_SetProgramName() and some environment variables; for example, if theprogram name is'/usr/local/bin/python', the prefix is'/usr/local'. Thereturned string points into static storage; the caller should not modify itsvalue. This corresponds to theprefix variable in the top-levelMakefile and the--prefix argument to theconfigurescript at build time. The value is available to Python code assys.prefix.It is only useful on Unix. See also the next function.

wchar_t*Py_GetExecPrefix()¶

Return theexec-prefix for installed platform-dependent files. This isderived through a number of complicated rules from the program name set withPy_SetProgramName() and some environment variables; for example, if theprogram name is'/usr/local/bin/python', the exec-prefix is'/usr/local'. The returned string points into static storage; the callershould not modify its value. This corresponds to theexec_prefixvariable in the top-levelMakefile and the--exec-prefixargument to theconfigure script at build time. The value isavailable to Python code assys.exec_prefix. It is only useful on Unix.

Background: The exec-prefix differs from the prefix when platform dependentfiles (such as executables and shared libraries) are installed in a differentdirectory tree. In a typical installation, platform dependent files may beinstalled in the/usr/local/plat subtree while platform independent maybe installed in/usr/local.

Generally speaking, a platform is a combination of hardware and softwarefamilies, e.g. Sparc machines running the Solaris 2.x operating system areconsidered the same platform, but Intel machines running Solaris 2.x are anotherplatform, and Intel machines running Linux are yet another platform. Differentmajor revisions of the same operating system generally also form differentplatforms. Non-Unix operating systems are a different story; the installationstrategies on those systems are so different that the prefix and exec-prefix aremeaningless, and set to the empty string. Note that compiled Python bytecodefiles are platform independent (but not independent from the Python version bywhich they were compiled!).

System administrators will know how to configure themount orautomount programs to share/usr/local between platformswhile having/usr/local/plat be a different filesystem for eachplatform.

wchar_t*Py_GetProgramFullPath()¶

Return the full program name of the Python executable; this is computed as aside-effect of deriving the default module search path from the program name(set byPy_SetProgramName() above). The returned string points intostatic storage; the caller should not modify its value. The value is availableto Python code assys.executable.

wchar_t*Py_GetPath()¶

Return the default module search path; this is computed from the program name(set byPy_SetProgramName() above) and some environment variables.The returned string consists of a series of directory names separated by aplatform dependent delimiter character. The delimiter character is':'on Unix and Mac OS X,';' on Windows. The returned string points intostatic storage; the caller should not modify its value. The listsys.path is initialized with this value on interpreter startup; itcan be (and usually is) modified later to change the search path for loadingmodules.

voidPy_SetPath(const wchar_t *)¶

Set the default module search path. If this function is called beforePy_Initialize(), thenPy_GetPath() won’t attempt to compute adefault search path but uses the one provided instead. This is useful ifPython is embedded by an application that has full knowledge of the locationof all modules. The path components should be separated by the platformdependent delimiter character, which is':' on Unix and Mac OS X,';'on Windows.

This also causessys.executable to be set to the programfull path (seePy_GetProgramFullPath()) and forsys.prefix andsys.exec_prefix to be empty. It is up to the caller to modify theseif required after callingPy_Initialize().

UsePy_DecodeLocale() to decode a bytes string to get awchar_* string.

The path argument is copied internally, so the caller may free it after thecall completes.

Changed in version 3.8:The program full path is now used forsys.executable, insteadof the program name.

const char*Py_GetVersion()¶

Return the version of this Python interpreter. This is a string that lookssomething like

"3.0a5+ (py3k:63103M, May 12 2008, 00:53:55)\n[GCC 4.2.3]"

The first word (up to the first space character) is the current Python version;the first three characters are the major and minor version separated by aperiod. The returned string points into static storage; the caller should notmodify its value. The value is available to Python code assys.version.

const char*Py_GetPlatform()¶

Return the platform identifier for the current platform. On Unix, this isformed from the “official” name of the operating system, converted to lowercase, followed by the major revision number; e.g., for Solaris 2.x, which isalso known as SunOS 5.x, the value is'sunos5'. On Mac OS X, it is'darwin'. On Windows, it is'win'. The returned string points intostatic storage; the caller should not modify its value. The value is availableto Python code assys.platform.

const char*Py_GetCopyright()¶

Return the official copyright string for the current Python version, for example

'Copyright1991-1995StichtingMathematischCentrum,Amsterdam'

The returned string points into static storage; the caller should not modify itsvalue. The value is available to Python code assys.copyright.

const char*Py_GetCompiler()¶

Return an indication of the compiler used to build the current Python version,in square brackets, for example:

"[GCC 2.7.2.2]"

The returned string points into static storage; the caller should not modify itsvalue. The value is available to Python code as part of the variablesys.version.

const char*Py_GetBuildInfo()¶

Return information about the sequence number and build date and time of thecurrent Python interpreter instance, for example

"#67, Aug  1 1997, 22:34:28"

The returned string points into static storage; the caller should not modify itsvalue. The value is available to Python code as part of the variablesys.version.

voidPySys_SetArgvEx(int argc, wchar_t **argv, int updatepath)¶

Setsys.argv based onargc andargv. These parameters aresimilar to those passed to the program’smain() function with thedifference that the first entry should refer to the script file to beexecuted rather than the executable hosting the Python interpreter. If thereisn’t a script that will be run, the first entry inargv can be an emptystring. If this function fails to initializesys.argv, a fatalcondition is signalled usingPy_FatalError().

Ifupdatepath is zero, this is all the function does. Ifupdatepathis non-zero, the function also modifiessys.path according to thefollowing algorithm:

• If the name of an existing script is passed inargv[0], the absolutepath of the directory where the script is located is prepended tosys.path.

• Otherwise (that is, ifargc is0 orargv[0] doesn’t pointto an existing file name), an empty string is prepended tosys.path, which is the same as prepending the current workingdirectory (".").

UsePy_DecodeLocale() to decode a bytes string to get awchar_* string.

Note

It is recommended that applications embedding the Python interpreterfor purposes other than executing a single script pass0 asupdatepath,and updatesys.path themselves if desired.SeeCVE-2008-5983.

On versions before 3.1.3, you can achieve the same effect by manuallypopping the firstsys.path element after having calledPySys_SetArgv(), for example using:

PyRun_SimpleString("import sys; sys.path.pop(0)\n");

New in version 3.1.3.

voidPySys_SetArgv(int argc, wchar_t **argv)¶

This function works likePySys_SetArgvEx() withupdatepath setto1 unless thepython interpreter was started with the-I.

UsePy_DecodeLocale() to decode a bytes string to get awchar_* string.

Changed in version 3.4:Theupdatepath value depends on-I.

voidPy_SetPythonHome(const wchar_t *home)¶

Set the default “home” directory, that is, the location of the standardPython libraries. SeePYTHONHOME for the meaning of theargument string.

The argument should point to a zero-terminated character string in staticstorage whose contents will not change for the duration of the program’sexecution. No code in the Python interpreter will change the contents ofthis storage.

UsePy_DecodeLocale() to decode a bytes string to get awchar_* string.

w_char*Py_GetPythonHome()¶

Return the default “home”, that is, the value set by a previous call toPy_SetPythonHome(), or the value of thePYTHONHOMEenvironment variable if it is set.

Thread State and the Global Interpreter Lock¶

The Python interpreter is not fully thread-safe. In order to supportmulti-threaded Python programs, there’s a global lock, called theglobalinterpreter lock orGIL, that must be held by the current thread beforeit can safely access Python objects. Without the lock, even the simplestoperations could cause problems in a multi-threaded program: for example, whentwo threads simultaneously increment the reference count of the same object, thereference count could end up being incremented only once instead of twice.

Therefore, the rule exists that only the thread that has acquired theGIL may operate on Python objects or call Python/C API functions.In order to emulate concurrency of execution, the interpreter regularlytries to switch threads (seesys.setswitchinterval()). The lock is alsoreleased around potentially blocking I/O operations like reading or writinga file, so that other Python threads can run in the meantime.

The Python interpreter keeps some thread-specific bookkeeping informationinside a data structure calledPyThreadState. There’s also oneglobal variable pointing to the currentPyThreadState: it canbe retrieved usingPyThreadState_Get().

Savethethreadstateinalocalvariable.Releasetheglobalinterpreterlock....DosomeblockingI/Ooperation...Reacquiretheglobalinterpreterlock.Restorethethreadstatefromthelocalvariable.

Py_BEGIN_ALLOW_THREADS...DosomeblockingI/Ooperation...Py_END_ALLOW_THREADS

PyThreadState*_save;_save=PyEval_SaveThread();...DosomeblockingI/Ooperation...PyEval_RestoreThread(_save);

PyGILState_STATEgstate;gstate=PyGILState_Ensure();/* Perform Python actions here. */result=CallSomeFunction();/* evaluate result or handle exception *//* Release the thread. No Python API allowed beyond this point. */PyGILState_Release(gstate);

Sub-interpreter support¶

While in most uses, you will only embed a single Python interpreter, thereare cases where you need to create several independent interpreters in thesame process and perhaps even in the same thread. Sub-interpreters allowyou to do that.

The “main” interpreter is the first one created when the runtime initializes.It is usually the only Python interpreter in a process. Unlike sub-interpreters,the main interpreter has unique process-global responsibilities like signalhandling. It is also responsible for execution during runtime initialization andis usually the active interpreter during runtime finalization. ThePyInterpreterState_Main() function returns a pointer to its state.

You can switch between sub-interpreters using thePyThreadState_Swap()function. You can create and destroy them using the following functions:

PyThreadState*Py_NewInterpreter()¶

Create a new sub-interpreter. This is an (almost) totally separate environmentfor the execution of Python code. In particular, the new interpreter hasseparate, independent versions of all imported modules, including thefundamental modulesbuiltins,__main__ andsys. Thetable of loaded modules (sys.modules) and the module search path(sys.path) are also separate. The new environment has nosys.argvvariable. It has new standard I/O stream file objectssys.stdin,sys.stdout andsys.stderr (however these refer to the same underlyingfile descriptors).

The return value points to the first thread state created in the newsub-interpreter. This thread state is made in the current thread state.Note that no actual thread is created; see the discussion of thread statesbelow. If creation of the new interpreter is unsuccessful,NULL isreturned; no exception is set since the exception state is stored in thecurrent thread state and there may not be a current thread state. (Like allother Python/C API functions, the global interpreter lock must be held beforecalling this function and is still held when it returns; however, unlike mostother Python/C API functions, there needn’t be a current thread state onentry.)

Extension modules are shared between (sub-)interpreters as follows:

• For modules using multi-phase initialization,e.g.PyModule_FromDefAndSpec(), a separate module object iscreated and initialized for each interpreter.Only C-level static and global variables are shared between thesemodule objects.

• For modules using single-phase initialization,e.g.PyModule_Create(), the first time a particular extensionis imported, it is initialized normally, and a (shallow) copy of itsmodule’s dictionary is squirreled away.When the same extension is imported by another (sub-)interpreter, a newmodule is initialized and filled with the contents of this copy; theextension’sinit function is not called.Objects in the module’s dictionary thus end up shared across(sub-)interpreters, which might cause unwanted behavior (seeBugs and caveats below).

  Note that this is different from what happens when an extension isimported after the interpreter has been completely re-initialized bycallingPy_FinalizeEx() andPy_Initialize(); in thatcase, the extension’sinitmodule functionis called again.As with multi-phase initialization, this means that only C-level staticand global variables are shared between these modules.

voidPy_EndInterpreter(PyThreadState *tstate)¶

Destroy the (sub-)interpreter represented by the given thread state. The giventhread state must be the current thread state. See the discussion of threadstates below. When the call returns, the current thread state isNULL. Allthread states associated with this interpreter are destroyed. (The globalinterpreter lock must be held before calling this function and is still heldwhen it returns.)Py_FinalizeEx() will destroy all sub-interpreters thathaven’t been explicitly destroyed at that point.

Asynchronous Notifications¶

A mechanism is provided to make asynchronous notifications to the maininterpreter thread. These notifications take the form of a functionpointer and a void pointer argument.

intPy_AddPendingCall(int (*func)(void *), void *arg)¶

Schedule a function to be called from the main interpreter thread. Onsuccess,0 is returned andfunc is queued for being called in themain thread. On failure,-1 is returned without setting any exception.

When successfully queued,func will beeventually called from themain interpreter thread with the argumentarg. It will be calledasynchronously with respect to normally running Python code, but withboth these conditions met:

• on abytecode boundary;

• with the main thread holding theglobal interpreter lock(func can therefore use the full C API).

func must return0 on success, or-1 on failure with an exceptionset.func won’t be interrupted to perform another asynchronousnotification recursively, but it can still be interrupted to switchthreads if the global interpreter lock is released.

This function doesn’t need a current thread state to run, and it doesn’tneed the global interpreter lock.

Warning

This is a low-level function, only useful for very special cases.There is no guarantee thatfunc will be called as quick aspossible. If the main thread is busy executing a system call,func won’t be called before the system call returns. Thisfunction is generallynot suitable for calling Python code fromarbitrary C threads. Instead, use thePyGILState API.

New in version 3.1.

Profiling and Tracing¶

The Python interpreter provides some low-level support for attaching profilingand execution tracing facilities. These are used for profiling, debugging, andcoverage analysis tools.

This C interface allows the profiling or tracing code to avoid the overhead ofcalling through Python-level callable objects, making a direct C function callinstead. The essential attributes of the facility have not changed; theinterface allows trace functions to be installed per-thread, and the basicevents reported to the trace function are the same as had been reported to thePython-level trace functions in previous versions.

int(*Py_tracefunc)(PyObject *obj,PyFrameObject *frame, int what,PyObject *arg)¶

The type of the trace function registered usingPyEval_SetProfile() andPyEval_SetTrace(). The first parameter is the object passed to theregistration function asobj,frame is the frame object to which the eventpertains,what is one of the constantsPyTrace_CALL,PyTrace_EXCEPTION,PyTrace_LINE,PyTrace_RETURN,PyTrace_C_CALL,PyTrace_C_EXCEPTION,PyTrace_C_RETURN,orPyTrace_OPCODE, andarg depends on the value ofwhat:

Value ofwhat	Meaning ofarg
PyTrace_CALL	AlwaysPy_None.
PyTrace_EXCEPTION	Exception information as returned bysys.exc_info().
PyTrace_LINE	AlwaysPy_None.
PyTrace_RETURN	Value being returned to the caller,orNULL if caused by an exception.
PyTrace_C_CALL	Function object being called.
PyTrace_C_EXCEPTION	Function object being called.
PyTrace_C_RETURN	Function object being called.
PyTrace_OPCODE	AlwaysPy_None.

intPyTrace_CALL¶

The value of thewhat parameter to aPy_tracefunc function when a newcall to a function or method is being reported, or a new entry into a generator.Note that the creation of the iterator for a generator function is not reportedas there is no control transfer to the Python bytecode in the correspondingframe.

intPyTrace_EXCEPTION¶

The value of thewhat parameter to aPy_tracefunc function when anexception has been raised. The callback function is called with this value forwhat when after any bytecode is processed after which the exception becomesset within the frame being executed. The effect of this is that as exceptionpropagation causes the Python stack to unwind, the callback is called uponreturn to each frame as the exception propagates. Only trace functions receivesthese events; they are not needed by the profiler.

intPyTrace_LINE¶

The value passed as thewhat parameter to aPy_tracefunc function(but not a profiling function) when a line-number event is being reported.It may be disabled for a frame by settingf_trace_lines to0 on that frame.

intPyTrace_RETURN¶

The value for thewhat parameter toPy_tracefunc functions when acall is about to return.

intPyTrace_C_CALL¶

The value for thewhat parameter toPy_tracefunc functions when a Cfunction is about to be called.

intPyTrace_C_EXCEPTION¶

The value for thewhat parameter toPy_tracefunc functions when a Cfunction has raised an exception.

intPyTrace_C_RETURN¶

The value for thewhat parameter toPy_tracefunc functions when a Cfunction has returned.

intPyTrace_OPCODE¶

The value for thewhat parameter toPy_tracefunc functions (but notprofiling functions) when a new opcode is about to be executed. This event isnot emitted by default: it must be explicitly requested by settingf_trace_opcodes to1 on the frame.

voidPyEval_SetProfile(Py_tracefunc func,PyObject *obj)¶

Set the profiler function tofunc. Theobj parameter is passed to thefunction as its first parameter, and may be any Python object, orNULL. Ifthe profile function needs to maintain state, using a different value forobjfor each thread provides a convenient and thread-safe place to store it. Theprofile function is called for all monitored events exceptPyTrace_LINEPyTrace_OPCODE andPyTrace_EXCEPTION.

voidPyEval_SetTrace(Py_tracefunc func,PyObject *obj)¶

Set the tracing function tofunc. This is similar toPyEval_SetProfile(), except the tracing function does receive line-numberevents and per-opcode events, but does not receive any event related to C functionobjects being called. Any trace function registered usingPyEval_SetTrace()will not receivePyTrace_C_CALL,PyTrace_C_EXCEPTION orPyTrace_C_RETURN as a value for thewhat parameter.

Advanced Debugger Support¶

These functions are only intended to be used by advanced debugging tools.

PyInterpreterState*PyInterpreterState_Head()¶

Return the interpreter state object at the head of the list of all such objects.

PyInterpreterState*PyInterpreterState_Main()¶

Return the main interpreter state object.

PyInterpreterState*PyInterpreterState_Next(PyInterpreterState *interp)¶

Return the next interpreter state object afterinterp from the list of allsuch objects.

PyThreadState *PyInterpreterState_ThreadHead(PyInterpreterState *interp)¶

Return the pointer to the firstPyThreadState object in the list ofthreads associated with the interpreterinterp.

PyThreadState*PyThreadState_Next(PyThreadState *tstate)¶

Return the next thread state object aftertstate from the list of all suchobjects belonging to the samePyInterpreterState object.

Thread Local Storage Support¶

The Python interpreter provides low-level support for thread-local storage(TLS) which wraps the underlying native TLS implementation to support thePython-level thread local storage API (threading.local). TheCPython C level APIs are similar to those offered by pthreads and Windows:use a thread key and functions to associate avoid* value perthread.

The GIL doesnot need to be held when calling these functions; they supplytheir own locking.

Note thatPython.h does not include the declaration of the TLS APIs,you need to includepythread.h to use thread-local storage.