.. highlight:: c

.. _os:

Operating System Utilities

.. c:function:: PyObject* PyOS_FSPath(PyObject *path)

Return the file system representation for path. If the object is a :class:str or :class:bytes object, then a new :term:strong reference is returned. If the object implements the :class:os.PathLike interface, then :meth:~os.PathLike.__fspath__ is returned as long as it is a :class:str or :class:bytes object. Otherwise :exc:TypeError is raised and NULL is returned.

.. versionadded:: 3.6

.. c:function:: int Py_FdIsInteractive(FILE *fp, const char *filename)

Return true (nonzero) if the standard I/O file fp with name filename is deemed interactive. This is the case for files for which isatty(fileno(fp)) is true. If the :c:member:PyConfig.interactive is non-zero, this function also returns true if the filename pointer is NULL or if the name is equal to one of the strings '<stdin>' or '???'.

This function must not be called before Python is initialized.

.. c:function:: void PyOS_BeforeFork()

Function to prepare some internal state before a process fork. This should be called before calling :c:func:fork or any similar function that clones the current process. Only available on systems where :c:func:fork is defined.

.. warning:: The C :c:func:fork call should only be made from the :ref:"main" thread <fork-and-threads> (of the :ref:"main" interpreter <sub-interpreter-support>). The same is true for PyOS_BeforeFork().

.. versionadded:: 3.7

.. c:function:: void PyOS_AfterFork_Parent()

Function to update some internal state after a process fork. This should be called from the parent process after calling :c:func:fork or any similar function that clones the current process, regardless of whether process cloning was successful. Only available on systems where :c:func:fork is defined.

.. warning:: The C :c:func:fork call should only be made from the :ref:"main" thread <fork-and-threads> (of the :ref:"main" interpreter <sub-interpreter-support>). The same is true for PyOS_AfterFork_Parent().

.. versionadded:: 3.7

.. c:function:: void PyOS_AfterFork_Child()

Function to update internal interpreter state after a process fork. This must be called from the child process after calling :c:func:fork, or any similar function that clones the current process, if there is any chance the process will call back into the Python interpreter. Only available on systems where :c:func:fork is defined.

.. warning:: The C :c:func:fork call should only be made from the :ref:"main" thread <fork-and-threads> (of the :ref:"main" interpreter <sub-interpreter-support>). The same is true for PyOS_AfterFork_Child().

.. versionadded:: 3.7

.. seealso:: :func:os.register_at_fork allows registering custom Python functions to be called by :c:func:PyOS_BeforeFork(), :c:func:PyOS_AfterFork_Parent and :c:func:PyOS_AfterFork_Child.

.. c:function:: void PyOS_AfterFork()

Function to update some internal state after a process fork; this should be called in the new process if the Python interpreter will continue to be used. If a new executable is loaded into the new process, this function does not need to be called.

.. deprecated:: 3.7 This function is superseded by :c:func:PyOS_AfterFork_Child().

.. c:function:: int PyOS_CheckStack()

.. index:: single: USE_STACKCHECK (C macro)

Return true when the interpreter runs out of stack space. This is a reliable check, but is only available when :c:macro:!USE_STACKCHECK is defined (currently on certain versions of Windows using the Microsoft Visual C++ compiler). :c:macro:!USE_STACKCHECK will be defined automatically; you should never change the definition in your own code.

.. c:type:: void (*PyOS_sighandler_t)(int)

.. c:function:: PyOS_sighandler_t PyOS_getsig(int i)

Return the current signal handler for signal i. This is a thin wrapper around either :c:func:!sigaction or :c:func:!signal. Do not call those functions directly!

.. c:function:: PyOS_sighandler_t PyOS_setsig(int i, PyOS_sighandler_t h)

Set the signal handler for signal i to be h; return the old signal handler. This is a thin wrapper around either :c:func:!sigaction or :c:func:!signal. Do not call those functions directly!

.. c:function:: int PyOS_InterruptOccurred(void)

Check if a :c:macro:!SIGINT signal has been received.

Returns 1 if a :c:macro:!SIGINT has occurred and clears the signal flag, or 0 otherwise.

In most cases, you should prefer :c:func:PyErr_CheckSignals over this function. :c:func:!PyErr_CheckSignals invokes the appropriate signal handlers for all pending signals, allowing Python code to handle the signal properly. This function only detects :c:macro:!SIGINT and does not invoke any Python signal handlers.

This function is async-signal-safe and this function cannot fail. The caller must hold an :term:attached thread state.

.. c:function:: wchar_t* Py_DecodeLocale(const char* arg, size_t *size)

.. warning:: This function should not be called directly: use the :c:type:PyConfig API with the :c:func:PyConfig_SetBytesString function which ensures that :ref:Python is preinitialized <c-preinit>.

  This function must not be called before :ref:`Python is preinitialized
  <c-preinit>` and so that the LC_CTYPE locale is properly configured: see
  the :c:func:`Py_PreInitialize` function.

Decode a byte string from the :term:filesystem encoding and error handler. If the error handler is :ref:surrogateescape error handler <surrogateescape>, undecodable bytes are decoded as characters in range U+DC80..U+DCFF; and if a byte sequence can be decoded as a surrogate character, the bytes are escaped using the surrogateescape error handler instead of decoding them.

Return a pointer to a newly allocated wide character string, use :c:func:PyMem_RawFree to free the memory. If size is not NULL, write the number of wide characters excluding the null character into *size

Return NULL on decoding error or memory allocation error. If size is not NULL, *size is set to (size_t)-1 on memory error or set to (size_t)-2 on decoding error.

The :term:filesystem encoding and error handler are selected by :c:func:PyConfig_Read: see :c:member:~PyConfig.filesystem_encoding and :c:member:~PyConfig.filesystem_errors members of :c:type:PyConfig.

Decoding errors should never happen, unless there is a bug in the C library.

Use the :c:func:Py_EncodeLocale function to encode the character string back to a byte string.

.. seealso::

  The :c:func:`PyUnicode_DecodeFSDefaultAndSize` and
  :c:func:`PyUnicode_DecodeLocaleAndSize` functions.

.. versionadded:: 3.5

.. versionchanged:: 3.7 The function now uses the UTF-8 encoding in the :ref:Python UTF-8 Mode <utf8-mode>.

.. versionchanged:: 3.8 The function now uses the UTF-8 encoding on Windows if :c:member:PyPreConfig.legacy_windows_fs_encoding is zero;

.. c:function:: char* Py_EncodeLocale(const wchar_t *text, size_t *error_pos)

Encode a wide character string to the :term:filesystem encoding and error handler. If the error handler is :ref:surrogateescape error handler <surrogateescape>, surrogate characters in the range U+DC80..U+DCFF are converted to bytes 0x80..0xFF.

Return a pointer to a newly allocated byte string, use :c:func:PyMem_Free to free the memory. Return NULL on encoding error or memory allocation error.

If error_pos is not NULL, *error_pos is set to (size_t)-1 on success, or set to the index of the invalid character on encoding error.

The :term:filesystem encoding and error handler are selected by :c:func:PyConfig_Read: see :c:member:~PyConfig.filesystem_encoding and :c:member:~PyConfig.filesystem_errors members of :c:type:PyConfig.

Use the :c:func:Py_DecodeLocale function to decode the bytes string back to a wide character string.

.. warning:: This function must not be called before :ref:Python is preinitialized <c-preinit> and so that the LC_CTYPE locale is properly configured: see the :c:func:Py_PreInitialize function.

.. seealso::

  The :c:func:`PyUnicode_EncodeFSDefault` and
  :c:func:`PyUnicode_EncodeLocale` functions.

.. versionadded:: 3.5

.. versionchanged:: 3.7 The function now uses the UTF-8 encoding in the :ref:Python UTF-8 Mode <utf8-mode>.

.. versionchanged:: 3.8 The function now uses the UTF-8 encoding on Windows if :c:member:PyPreConfig.legacy_windows_fs_encoding is zero.

.. c:function:: FILE* Py_fopen(PyObject *path, const char *mode)

Similar to :c:func:!fopen, but path is a Python object and an exception is set on error.

path must be a :class:str object, a :class:bytes object, or a :term:path-like object.

On success, return the new file pointer. On error, set an exception and return NULL.

The file must be closed by :c:func:Py_fclose rather than calling directly :c:func:!fclose.

The file descriptor is created non-inheritable (:pep:446).

The caller must have an :term:attached thread state.

.. versionadded:: 3.14

.. c:function:: int Py_fclose(FILE *file)

Close a file that was opened by :c:func:Py_fopen.

On success, return 0. On error, return EOF and errno is set to indicate the error. In either case, any further access (including another call to :c:func:Py_fclose) to the stream results in undefined behavior.

.. versionadded:: 3.14

.. _systemfunctions:

System Functions

These are utility functions that make functionality from the :mod:sys module accessible to C code. They all work with the current interpreter thread's :mod:sys module's dict, which is contained in the internal thread state structure.

.. c:function:: PyObject *PySys_GetAttr(PyObject *name)

Get the attribute name of the :mod:sys module. Return a :term:strong reference. Raise :exc:RuntimeError and return NULL if it does not exist or if the :mod:sys module cannot be found.

If the non-existing object should not be treated as a failure, you can use :c:func:PySys_GetOptionalAttr instead.

.. versionadded:: 3.15

.. c:function:: PyObject *PySys_GetAttrString(const char *name)

This is the same as :c:func:PySys_GetAttr, but name is specified as a :c:expr:const char* UTF-8 encoded bytes string, rather than a :c:expr:PyObject*.

If the non-existing object should not be treated as a failure, you can use :c:func:PySys_GetOptionalAttrString instead.

.. versionadded:: 3.15

.. c:function:: int PySys_GetOptionalAttr(PyObject *name, PyObject **result)

Variant of :c:func:PySys_GetAttr which doesn't raise exception if the object does not exist.

• Set *result to a new :term:strong reference to the object and return 1 if the object exists.
• Set *result to NULL and return 0 without setting an exception if the object does not exist.
• Set an exception, set *result to NULL, and return -1, if an error occurred.

.. versionadded:: 3.15

.. c:function:: int PySys_GetOptionalAttrString(const char *name, PyObject **result)

This is the same as :c:func:PySys_GetOptionalAttr, but name is specified as a :c:expr:const char* UTF-8 encoded bytes string, rather than a :c:expr:PyObject*.

.. versionadded:: 3.15

.. c:function:: PyObject *PySys_GetObject(const char *name)

Similar to :c:func:PySys_GetAttrString, but return a :term:borrowed reference and return NULL without setting exception on failure.

Preserves exception that was set before the call.

.. c:function:: int PySys_SetObject(const char *name, PyObject *v)

Set name in the :mod:sys module to v unless v is NULL, in which case name is deleted from the sys module. Returns 0 on success, -1 on error.

.. c:function:: void PySys_WriteStdout(const char *format, ...)

Write the output string described by format to :data:sys.stdout. No exceptions are raised, even if truncation occurs (see below).

format should limit the total size of the formatted output string to 1000 bytes or less -- after 1000 bytes, the output string is truncated. In particular, this means that no unrestricted "%s" formats should occur; these should be limited using "%.<N>s" where <N> is a decimal number calculated so that <N> plus the maximum size of other formatted text does not exceed 1000 bytes. Also watch out for "%f", which can print hundreds of digits for very large numbers.

If a problem occurs, or :data:sys.stdout is unset, the formatted message is written to the real (C level) stdout.

.. c:function:: void PySys_WriteStderr(const char *format, ...)

As :c:func:PySys_WriteStdout, but write to :data:sys.stderr or stderr instead.

.. c:function:: void PySys_FormatStdout(const char *format, ...)

Function similar to PySys_WriteStdout() but format the message using :c:func:PyUnicode_FromFormatV and don't truncate the message to an arbitrary length.

.. versionadded:: 3.2

.. c:function:: void PySys_FormatStderr(const char *format, ...)

As :c:func:PySys_FormatStdout, but write to :data:sys.stderr or stderr instead.

.. versionadded:: 3.2

.. c:function:: PyObject *PySys_GetXOptions()

Return the current dictionary of :option:-X options, similarly to :data:sys._xoptions. On error, NULL is returned and an exception is set.

.. versionadded:: 3.2

.. c:function:: int PySys_Audit(const char *event, const char *format, ...)

Raise an auditing event with any active hooks. Return zero for success and non-zero with an exception set on failure.

The event string argument must not be NULL.

If any hooks have been added, format and other arguments will be used to construct a tuple to pass. Apart from N, the same format characters as used in :c:func:Py_BuildValue are available. If the built value is not a tuple, it will be added into a single-element tuple.

The N format option must not be used. It consumes a reference, but since there is no way to know whether arguments to this function will be consumed, using it may cause reference leaks.

Note that # format characters should always be treated as :c:type:Py_ssize_t, regardless of whether PY_SSIZE_T_CLEAN was defined.

:func:sys.audit performs the same function from Python code.

See also :c:func:PySys_AuditTuple.

.. versionadded:: 3.8

.. versionchanged:: 3.8.2

  Require :c:type:`Py_ssize_t` for ``#`` format characters. Previously, an
  unavoidable deprecation warning was raised.

.. c:function:: int PySys_AuditTuple(const char *event, PyObject *args)

Similar to :c:func:PySys_Audit, but pass arguments as a Python object. args must be a :class:tuple. To pass no arguments, args can be NULL.

.. versionadded:: 3.13

.. c:function:: int PySys_AddAuditHook(Py_AuditHookFunction hook, void *userData)

Append the callable hook to the list of active auditing hooks. Return zero on success and non-zero on failure. If the runtime has been initialized, also set an error on failure. Hooks added through this API are called for all interpreters created by the runtime.

The userData pointer is passed into the hook function. Since hook functions may be called from different runtimes, this pointer should not refer directly to Python state.

This function is safe to call before :c:func:Py_Initialize. When called after runtime initialization, existing audit hooks are notified and may silently abort the operation by raising an error subclassed from :class:Exception (other errors will not be silenced).

The hook function is always called with an :term:attached thread state by the Python interpreter that raised the event.

See :pep:578 for a detailed description of auditing. Functions in the runtime and standard library that raise events are listed in the :ref:audit events table <audit-events>. Details are in each function's documentation.

.. audit-event:: sys.addaudithook "" c.PySys_AddAuditHook

  If the interpreter is initialized, this function raises an auditing event
  ``sys.addaudithook`` with no arguments. If any existing hooks raise an
  exception derived from :class:`Exception`, the new hook will not be
  added and the exception is cleared. As a result, callers cannot assume
  that their hook has been added unless they control all existing hooks.

.. c:namespace:: NULL .. c:type:: int (*Py_AuditHookFunction) (const char *event, PyObject *args, void *userData)

  The type of the hook function.
  *event* is the C string event argument passed to :c:func:`PySys_Audit` or
  :c:func:`PySys_AuditTuple`.
  *args* is guaranteed to be a :c:type:`PyTupleObject`.
  *userData* is the argument passed to PySys_AddAuditHook().

.. versionadded:: 3.8

.. _processcontrol:

Process Control

.. c:function:: void Py_FatalError(const char *message)

.. index:: single: abort (C function)

Print a fatal error message and kill the process. No cleanup is performed. This function should only be invoked when a condition is detected that would make it dangerous to continue using the Python interpreter; e.g., when the object administration appears to be corrupted. On Unix, the standard C library function :c:func:!abort is called which will attempt to produce a :file:core file.

The Py_FatalError() function is replaced with a macro which logs automatically the name of the current function, unless the Py_LIMITED_API macro is defined.

.. versionchanged:: 3.9 Log the function name automatically.

.. c:function:: void Py_Exit(int status)

.. index:: single: Py_FinalizeEx (C function) single: exit (C function)

Exit the current process. This calls :c:func:Py_FinalizeEx and then calls the standard C library function exit(status). If :c:func:Py_FinalizeEx indicates an error, the exit status is set to 120.

.. versionchanged:: 3.6 Errors from finalization no longer ignored.

.. c:function:: int Py_AtExit(void (*func) ())

.. index:: single: Py_FinalizeEx (C function) single: cleanup functions

Register a cleanup function to be called by :c:func:Py_FinalizeEx. The cleanup function will be called with no arguments and should return no value. At most 32 cleanup functions can be registered. When the registration is successful, :c:func:Py_AtExit returns 0; on failure, it returns -1. The cleanup function registered last is called first. Each cleanup function will be called at most once. Since Python's internal finalization will have completed before the cleanup function, no Python APIs should be called by func.

.. seealso::

  :c:func:`PyUnstable_AtExit` for passing a ``void *data`` argument.