# Operating System Utilities

PyObject* `PyOS_FSPath`(PyObject *path)
  Return value: New reference.

  Return the file system representation for path. If the object is a `str` or `bytes` object, then its reference count is incremented. If the object implements the `os.PathLike` interface, then `__fspath__()` is returned as long as it is a `str` or `bytes` object. Otherwise `TypeError` is raised and `NULL` is returned.

  New in version 3.6.

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 global flag `Py_InteractiveFlag` is true, this function also returns true if the filename pointer is `NULL` or if the name is equal to one of the strings `'<stdin>'` or `'???'`.

void `PyOS_BeforeFork`()

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

  Warning

  The C `fork()` call should only be made from the “main” thread (of the “main” interpreter). The same is true for `PyOS_BeforeFork()`.

  New in version 3.7.

void `PyOS_AfterFork_Parent`()

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

  Warning

  The C `fork()` call should only be made from the “main” thread (of the “main” interpreter). The same is true for `PyOS_AfterFork_Parent()`.

  New in version 3.7.

void `PyOS_AfterFork_Child`()

  Function to update internal interpreter state after a process fork. This must be called from the child process after calling `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 `fork()` is defined.

  Warning

  The C `fork()` call should only be made from the “main” thread (of the “main” interpreter). The same is true for `PyOS_AfterFork_Child()`.

  New in version 3.7.

  See also

  `os.register_at_fork()` allows registering custom Python functions to be called by `PyOS_BeforeFork()`, `PyOS_AfterFork_Parent()` and `PyOS_AfterFork_Child()`.

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 since version 3.7: This function is superseded by `PyOS_AfterFork_Child()`.

int `PyOS_CheckStack`()

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

PyOS_sighandler_t `PyOS_getsig`(int i)

  Return the current signal handler for signal i. This is a thin wrapper around either `sigaction()` or `signal()`. Do not call those functions directly! `PyOS_sighandler_t` is a typedef alias for `void (*)(int)`.

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 `sigaction()` or `signal()`. Do not call those functions directly! `PyOS_sighandler_t` is a typedef alias for `void (*)(int)`.

wchar_t* `Py_DecodeLocale`(const char* arg, size_t *size)

  Decode a byte string from the locale encoding with the surrogateescape error handler: undecodable bytes are decoded as characters in range U+DC80..U+DCFF. If a byte sequence can be decoded as a surrogate character, escape the bytes using the surrogateescape error handler instead of decoding them.

  Encoding, highest priority to lowest priority:

  - `UTF-8` on macOS, Android, and VxWorks;

  - `UTF-8` on Windows if `Py_LegacyWindowsFSEncodingFlag` is zero;

  - `UTF-8` if the Python UTF-8 mode is enabled;

  - `ASCII` if the `LC_CTYPE` locale is `"C"`, `nl_langinfo(CODESET)` returns the `ASCII` encoding (or an alias), and `mbstowcs()` and `wcstombs()` functions uses the `ISO-8859-1` encoding.

  - the current locale encoding.

  Return a pointer to a newly allocated wide character string, use `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.

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

  Use the `Py_EncodeLocale()` function to encode the character string back to a byte string.

  See also

  The `PyUnicode_DecodeFSDefaultAndSize()` and `PyUnicode_DecodeLocaleAndSize()` functions.

  New in version 3.5.

  Changed in version 3.7: The function now uses the UTF-8 encoding in the UTF-8 mode.

  Changed in version 3.8: The function now uses the UTF-8 encoding on Windows if `Py_LegacyWindowsFSEncodingFlag` is zero;

char* `Py_EncodeLocale`(const wchar_t *text, size_t *error_pos)

  Encode a wide character string to the locale encoding with the surrogateescape error handler: surrogate characters in the range U+DC80..U+DCFF are converted to bytes 0x80..0xFF.

  Encoding, highest priority to lowest priority:

  - `UTF-8` on macOS, Android, and VxWorks;

  - `UTF-8` on Windows if `Py_LegacyWindowsFSEncodingFlag` is zero;

  - `UTF-8` if the Python UTF-8 mode is enabled;

  - `ASCII` if the `LC_CTYPE` locale is `"C"`, `nl_langinfo(CODESET)` returns the `ASCII` encoding (or an alias), and `mbstowcs()` and `wcstombs()` functions uses the `ISO-8859-1` encoding.

  - the current locale encoding.

  The function uses the UTF-8 encoding in the Python UTF-8 mode.

  Return a pointer to a newly allocated byte string, use `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.

  Use the `Py_DecodeLocale()` function to decode the bytes string back to a wide character string.

  See also

  The `PyUnicode_EncodeFSDefault()` and `PyUnicode_EncodeLocale()` functions.

  New in version 3.5.

  Changed in version 3.7: The function now uses the UTF-8 encoding in the UTF-8 mode.

  Changed in version 3.8: The function now uses the UTF-8 encoding on Windows if `Py_LegacyWindowsFSEncodingFlag` is zero;

# System Functions

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

PyObject *`PySys_GetObject`(const char *name)
  Return value: Borrowed reference.

  Return the object name from the `sys` module or `NULL` if it does not exist, without setting an exception.

int `PySys_SetObject`(const char *name, PyObject *v)

  Set name in the `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.

void `PySys_ResetWarnOptions`()

  Reset `sys.warnoptions` to an empty list. This function may be called prior to `Py_Initialize()`.

void `PySys_AddWarnOption`(const wchar_t *s)

  Append s to `sys.warnoptions`. This function must be called prior to `Py_Initialize()` in order to affect the warnings filter list.

void `PySys_AddWarnOptionUnicode`(PyObject *unicode)

  Append unicode to `sys.warnoptions`.

  Note: this function is not currently usable from outside the CPython implementation, as it must be called prior to the implicit import of `warnings` in `Py_Initialize()` to be effective, but can’t be called until enough of the runtime has been initialized to permit the creation of Unicode objects.

void `PySys_SetPath`(const wchar_t *path)

  Set `sys.path` to a list object of paths found in path which should be a list of paths separated with the platform’s search path delimiter (`:` on Unix, `;` on Windows).

void `PySys_WriteStdout`(const char *format, ...)

  Write the output string described by format to `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 `sys.stdout` is unset, the formatted message is written to the real (C level) stdout.

void `PySys_WriteStderr`(const char *format, ...)

  As `PySys_WriteStdout()`, but write to `sys.stderr` or stderr instead.

void `PySys_FormatStdout`(const char *format, ...)

  Function similar to PySys_WriteStdout() but format the message using `PyUnicode_FromFormatV()` and don’t truncate the message to an arbitrary length.

  New in version 3.2.

void `PySys_FormatStderr`(const char *format, ...)

  As `PySys_FormatStdout()`, but write to `sys.stderr` or stderr instead.

  New in version 3.2.

void `PySys_AddXOption`(const wchar_t *s)

  Parse s as a set of `-X` options and add them to the current options mapping as returned by `PySys_GetXOptions()`. This function may be called prior to `Py_Initialize()`.

  New in version 3.2.

PyObject *`PySys_GetXOptions`()
  Return value: Borrowed reference.

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

  New in version 3.2.

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.

  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 `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 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 `Py_ssize_t`, regardless of whether `PY_SSIZE_T_CLEAN` was defined.

  `sys.audit()` performs the same function from Python code.

  New in version 3.8.

  Changed in version 3.8.2: Require `Py_ssize_t` for `#` format characters. Previously, an unavoidable deprecation warning was raised.

int `PySys_AddAuditHook`(Py_AuditHookFunction hook, void *userData)

  Append the callable hook to the list of active auditing hooks. Return zero for 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 `Py_Initialize()`. When called after runtime initialization, existing audit hooks are notified and may silently abort the operation by raising an error subclassed from `Exception` (other errors will not be silenced).

  The hook function is of type `int (*)(const char *event, PyObject *args, void *userData)`, where args is guaranteed to be a `PyTupleObject`. The hook function is always called with the GIL held 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 audit events table. Details are in each function’s documentation.

  If the interpreter is initialized, this function raises a auditing event `sys.addaudithook` with no arguments. If any existing hooks raise an exception derived from `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.

  New in version 3.8.

# Process Control

void `Py_FatalError`(const char *message)

  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 `abort()` is called which will attempt to produce a `core` file.

void `Py_Exit`(int status)

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

  Changed in version 3.6: Errors from finalization no longer ignored.

int `Py_AtExit`(void (*func)())

  Register a cleanup function to be called by `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, `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.