Printing and clearing¶

void PyErr_Clear()¶

Part of the Stable ABI.

Clear the error indicator. If the error indicator is not set, there is no effect.

void PyErr_PrintEx(int set_sys_last_vars)¶

Part of the Stable ABI.

Print a standard traceback to sys.stderr and clear the error indicator. Unless the error is a SystemExit, in that case no traceback is printed and the Python process will exit with the error code specified by the SystemExit instance.

Call this function only when the error indicator is set. Otherwise it will cause a fatal error!

If set_sys_last_vars is nonzero, the variable sys.last_exc is set to the printed exception. For backwards compatibility, the deprecated variables sys.last_type, sys.last_value and sys.last_traceback are also set to the type, value and traceback of this exception, respectively.

Changed in version 3.12: The setting of sys.last_exc was added.

void PyErr_Print()¶

Part of the Stable ABI.

Alias for PyErr_PrintEx(1).

void PyErr_WriteUnraisable(PyObject *obj)¶

Part of the Stable ABI.

Call sys.unraisablehook() using the current exception and obj argument.

This utility function prints a warning message to sys.stderr when an exception has been set but it is impossible for the interpreter to actually raise the exception. It is used, for example, when an exception occurs in an __del__() method.

The function is called with a single argument obj that identifies the context in which the unraisable exception occurred. If possible, the repr of obj will be printed in the warning message. If obj is NULL, only the traceback is printed.

An exception must be set when calling this function.

Changed in version 3.4: Print a traceback. Print only traceback if obj is NULL.

Changed in version 3.8: Use sys.unraisablehook().

void PyErr_FormatUnraisable(const char *format, ...)¶

Similar to PyErr_WriteUnraisable(), but the format and subsequent parameters help format the warning message; they have the same meaning and values as in PyUnicode_FromFormat(). PyErr_WriteUnraisable(obj) is roughly equivalent to PyErr_FormatUnraisable("Exception ignored in: %R", obj). If format is NULL, only the traceback is printed.

Added in version 3.13.

void PyErr_DisplayException(PyObject *exc)¶

Part of the Stable ABI since version 3.12.

Print the standard traceback display of exc to sys.stderr, including chained exceptions and notes.

Added in version 3.12.

void PyErr_Display(PyObject *unused, PyObject *value, PyObject *tb)¶

Part of the Stable ABI.

Legacy variant of PyErr_DisplayException().

Print the exception value with its traceback to sys.stderr. If value has no traceback set, tb is used as its traceback. The first argument is ignored.

If sys.stderr is None, nothing is printed. If sys.stderr is not set, the exception is dumped to the C stderr stream instead.

Deprecated since version 3.12: Use PyErr_DisplayException() instead.

Raising exceptions¶

These functions help you set the current thread’s error indicator. For convenience, some of these functions will always return a NULL pointer for use in a return statement.

void PyErr_SetString(PyObject *type, const char *message)¶

Part of the Stable ABI.

This is the most common way to set the error indicator. The first argument specifies the exception type; it is normally one of the standard exceptions, e.g. PyExc_RuntimeError. You need not create a new strong reference to it (e.g. with Py_INCREF()). The second argument is an error message; it is decoded from 'utf-8'.

void PyErr_SetObject(PyObject *type, PyObject *value)¶

Part of the Stable ABI.

This function is similar to PyErr_SetString() but lets you specify an arbitrary Python object for the “value” of the exception.

PyObject *PyErr_Format(PyObject *exception, const char *format, ...)¶

Return value: Always NULL. Part of the Stable ABI.

This function sets the error indicator and returns NULL. exception should be a Python exception class. The format and subsequent parameters help format the error message; they have the same meaning and values as in PyUnicode_FromFormat(). format is an ASCII-encoded string.

PyObject *PyErr_FormatV(PyObject *exception, const char *format, va_list vargs)¶

Return value: Always NULL. Part of the Stable ABI since version 3.5.

Same as PyErr_Format(), but taking a va_list argument rather than a variable number of arguments.

Added in version 3.5.

void PyErr_SetNone(PyObject *type)¶

Part of the Stable ABI.

This is a shorthand for PyErr_SetObject(type, Py_None).

int PyErr_BadArgument()¶

Part of the Stable ABI.

This is a shorthand for PyErr_SetString(PyExc_TypeError, message), where message indicates that a built-in operation was invoked with an illegal argument. It is mostly for internal use.

PyObject *PyErr_NoMemory()¶

Return value: Always NULL. Part of the Stable ABI.

This is a shorthand for PyErr_SetNone(PyExc_MemoryError); it returns NULL so an object allocation function can write return PyErr_NoMemory(); when it runs out of memory.

PyObject *PyErr_SetFromErrno(PyObject *type)¶

Return value: Always NULL. Part of the Stable ABI.

This is a convenience function to raise an exception when a C library function has returned an error and set the C variable errno. It constructs a tuple object whose first item is the integer errno value and whose second item is the corresponding error message (gotten from strerror()), and then calls PyErr_SetObject(type, object). On Unix, when the errno value is EINTR, indicating an interrupted system call, this calls PyErr_CheckSignals(), and if that set the error indicator, leaves it set to that. The function always returns NULL, so a wrapper function around a system call can write return PyErr_SetFromErrno(type); when the system call returns an error.

PyObject *PyErr_SetFromErrnoWithFilenameObject(PyObject *type, PyObject *filenameObject)¶

Return value: Always NULL. Part of the Stable ABI.

Similar to PyErr_SetFromErrno(), with the additional behavior that if filenameObject is not NULL, it is passed to the constructor of type as a third parameter. In the case of OSError exception, this is used to define the filename attribute of the exception instance.

PyObject *PyErr_SetFromErrnoWithFilenameObjects(PyObject *type, PyObject *filenameObject, PyObject *filenameObject2)¶

Return value: Always NULL. Part of the Stable ABI since version 3.7.

Similar to PyErr_SetFromErrnoWithFilenameObject(), but takes a second filename object, for raising errors when a function that takes two filenames fails.

Added in version 3.4.

PyObject *PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)¶

Return value: Always NULL. Part of the Stable ABI.

Similar to PyErr_SetFromErrnoWithFilenameObject(), but the filename is given as a C string. filename is decoded from the filesystem encoding and error handler.

PyObject *PyErr_SetFromWindowsErr(int ierr)¶

Return value: Always NULL. Part of the Stable ABI on Windows since version 3.7.

This is a convenience function to raise OSError. If called with ierr of 0, the error code returned by a call to GetLastError() is used instead. It calls the Win32 function FormatMessage() to retrieve the Windows description of error code given by ierr or GetLastError(), then it constructs a OSError object with the winerror attribute set to the error code, the strerror attribute set to the corresponding error message (gotten from FormatMessage()), and then calls PyErr_SetObject(PyExc_OSError, object). This function always returns NULL.

Availability: Windows.

PyObject *PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)¶

Return value: Always NULL. Part of the Stable ABI on Windows since version 3.7.

Similar to PyErr_SetFromWindowsErr(), with an additional parameter specifying the exception type to be raised.

Availability: Windows.

PyObject *PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)¶

Return value: Always NULL. Part of the Stable ABI on Windows since version 3.7.

Similar to PyErr_SetFromWindowsErr(), with the additional behavior that if filename is not NULL, it is decoded from the filesystem encoding (os.fsdecode()) and passed to the constructor of OSError as a third parameter to be used to define the filename attribute of the exception instance.

Availability: Windows.

PyObject *PyErr_SetExcFromWindowsErrWithFilenameObject(PyObject *type, int ierr, PyObject *filename)¶

Return value: Always NULL. Part of the Stable ABI on Windows since version 3.7.

Similar to PyErr_SetExcFromWindowsErr(), with the additional behavior that if filename is not NULL, it is passed to the constructor of OSError as a third parameter to be used to define the filename attribute of the exception instance.

Availability: Windows.

PyObject *PyErr_SetExcFromWindowsErrWithFilenameObjects(PyObject *type, int ierr, PyObject *filename, PyObject *filename2)¶

Return value: Always NULL. Part of the Stable ABI on Windows since version 3.7.

Similar to PyErr_SetExcFromWindowsErrWithFilenameObject(), but accepts a second filename object.

Availability: Windows.

Added in version 3.4.

PyObject *PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, const char *filename)¶

Return value: Always NULL. Part of the Stable ABI on Windows since version 3.7.

Similar to PyErr_SetFromWindowsErrWithFilename(), with an additional parameter specifying the exception type to be raised.

Availability: Windows.

PyObject *PyErr_SetImportError(PyObject *msg, PyObject *name, PyObject *path)¶

Return value: Always NULL. Part of the Stable ABI since version 3.7.

This is a convenience function to raise ImportError. msg will be set as the exception’s message string. name and path, both of which can be NULL, will be set as the ImportError’s respective name and path attributes.

Added in version 3.3.

PyObject *PyErr_SetImportErrorSubclass(PyObject *exception, PyObject *msg, PyObject *name, PyObject *path)¶

Return value: Always NULL. Part of the Stable ABI since version 3.6.

Much like PyErr_SetImportError() but this function allows for specifying a subclass of ImportError to raise.

Added in version 3.6.

void PyErr_SyntaxLocationObject(PyObject *filename, int lineno, int col_offset)¶

Set file, line, and offset information for the current exception. If the current exception is not a SyntaxError, then it sets additional attributes, which make the exception printing subsystem think the exception is a SyntaxError.

Added in version 3.4.

void PyErr_RangedSyntaxLocationObject(PyObject *filename, int lineno, int col_offset, int end_lineno, int end_col_offset)¶

Similar to PyErr_SyntaxLocationObject(), but also sets the end_lineno and end_col_offset information for the current exception.

Added in version 3.10.

void PyErr_SyntaxLocationEx(const char *filename, int lineno, int col_offset)¶

Part of the Stable ABI since version 3.7.

Like PyErr_SyntaxLocationObject(), but filename is a byte string decoded from the filesystem encoding and error handler.

Added in version 3.2.

void PyErr_SyntaxLocation(const char *filename, int lineno)¶

Part of the Stable ABI.

Like PyErr_SyntaxLocationEx(), but the col_offset parameter is omitted.

void PyErr_BadInternalCall()¶

Part of the Stable ABI.

This is a shorthand for PyErr_SetString(PyExc_SystemError, message), where message indicates that an internal operation (e.g. a Python/C API function) was invoked with an illegal argument. It is mostly for internal use.

PyObject *PyErr_ProgramTextObject(PyObject *filename, int lineno)¶

Get the source line in filename at line lineno. filename should be a Python str object.

On success, this function returns a Python string object with the found line. On failure, this function returns NULL without an exception set.

PyObject *PyErr_ProgramText(const char *filename, int lineno)¶

Part of the Stable ABI.

Similar to PyErr_ProgramTextObject(), but filename is a const char*, which is decoded with the filesystem encoding and error handler, instead of a Python object reference.

Issuing warnings¶

Use these functions to issue warnings from C code. They mirror similar functions exported by the Python warnings module. They normally print a warning message to sys.stderr; however, it is also possible that the user has specified that warnings are to be turned into errors, and in that case they will raise an exception. It is also possible that the functions raise an exception because of a problem with the warning machinery. The return value is 0 if no exception is raised, or -1 if an exception is raised. (It is not possible to determine whether a warning message is actually printed, nor what the reason is for the exception; this is intentional.) If an exception is raised, the caller should do its normal exception handling (for example, Py_DECREF() owned references and return an error value).

int PyErr_WarnEx(PyObject *category, const char *message, Py_ssize_t stack_level)¶

Part of the Stable ABI.

Issue a warning message. The category argument is a warning category (see below) or NULL; the message argument is a UTF-8 encoded string. stack_level is a positive number giving a number of stack frames; the warning will be issued from the currently executing line of code in that stack frame. A stack_level of 1 is the function calling PyErr_WarnEx(), 2 is the function above that, and so forth.

Warning categories must be subclasses of PyExc_Warning; PyExc_Warning is a subclass of PyExc_Exception; the default warning category is PyExc_RuntimeWarning. The standard Python warning categories are available as global variables whose names are enumerated at Warning types.

For information about warning control, see the documentation for the warnings module and the -W option in the command line documentation. There is no C API for warning control.

int PyErr_Warn(PyObject *category, const char *message)¶

Equivalent to PyErr_WarnEx(category, message, 1).

int PyErr_WarnExplicitObject(PyObject *category, PyObject *message, PyObject *filename, int lineno, PyObject *module, PyObject *registry)¶

Issue a warning message with explicit control over all warning attributes. This is a straightforward wrapper around the Python function warnings.warn_explicit(); see there for more information. The module and registry arguments may be set to NULL to get the default effect described there.

Added in version 3.4.

int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)¶

Part of the Stable ABI.

Similar to PyErr_WarnExplicitObject() except that message and module are UTF-8 encoded strings, and filename is decoded from the filesystem encoding and error handler.

int PyErr_WarnFormat(PyObject *category, Py_ssize_t stack_level, const char *format, ...)¶

Part of the Stable ABI.

Function similar to PyErr_WarnEx(), but uses PyUnicode_FromFormat() to format the warning message. format is an ASCII-encoded string.

Added in version 3.2.

int PyErr_WarnExplicitFormat(PyObject *category, const char *filename, int lineno, const char *module, PyObject *registry, const char *format, ...)¶

Similar to PyErr_WarnExplicit(), but uses PyUnicode_FromFormat() to format the warning message. format is an ASCII-encoded string.

Added in version 3.2.

int PyErr_ResourceWarning(PyObject *source, Py_ssize_t stack_level, const char *format, ...)¶

Part of the Stable ABI since version 3.6.

Function similar to PyErr_WarnFormat(), but category is ResourceWarning and it passes source to warnings.WarningMessage.

Added in version 3.6.

Querying the error indicator¶

PyObject *PyErr_Occurred()¶

Return value: Borrowed reference. Part of the Stable ABI.

Test whether the error indicator is set. If set, return the exception type (the first argument to the last call to one of the PyErr_Set* functions or to PyErr_Restore()). If not set, return NULL. You do not own a reference to the return value, so you do not need to Py_DECREF() it.

The caller must have an attached thread state.

Note

Do not compare the return value to a specific exception; use PyErr_ExceptionMatches() instead, shown below. (The comparison could easily fail since the exception may be an instance instead of a class, in the case of a class exception, or it may be a subclass of the expected exception.)

int PyErr_ExceptionMatches(PyObject *exc)¶

Part of the Stable ABI.

Equivalent to PyErr_GivenExceptionMatches(PyErr_Occurred(), exc). This should only be called when an exception is actually set; a memory access violation will occur if no exception has been raised.

int PyErr_GivenExceptionMatches(PyObject *given, PyObject *exc)¶

Part of the Stable ABI.

Return true if the given exception matches the exception type in exc. If exc is a class object, this also returns true when given is an instance of a subclass. If exc is a tuple, all exception types in the tuple (and recursively in subtuples) are searched for a match.

PyObject *PyErr_GetRaisedException(void)¶

Return value: New reference. Part of the Stable ABI since version 3.12.

Return the exception currently being raised, clearing the error indicator at the same time. Return NULL if the error indicator is not set.

This function is used by code that needs to catch exceptions, or code that needs to save and restore the error indicator temporarily.

For example:

{
   PyObject *exc = PyErr_GetRaisedException();

   /* ... code that might produce other errors ... */

   PyErr_SetRaisedException(exc);
}

See also

PyErr_GetHandledException(), to save the exception currently being handled.

Added in version 3.12.

void PyErr_SetRaisedException(PyObject *exc)¶

Part of the Stable ABI since version 3.12.

Set exc as the exception currently being raised, clearing the existing exception if one is set. If exc is NULL, just clear the existing exception.

exc must be a valid exception or NULL.

This call “steals” a reference to exc.

Added in version 3.12.

void PyErr_Fetch(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)¶

Part of the Stable ABI.

Deprecated since version 3.12: Use PyErr_GetRaisedException() instead.

Retrieve the error indicator into three variables whose addresses are passed. If the error indicator is not set, set all three variables to NULL. If it is set, it will be cleared and you own a reference to each object retrieved. The value and traceback object may be NULL even when the type object is not.

Note

This function is normally only used by legacy code that needs to catch exceptions or save and restore the error indicator temporarily.

For example:

{
   PyObject *type, *value, *traceback;
   PyErr_Fetch(&type, &value, &traceback);

   /* ... code that might produce other errors ... */

   PyErr_Restore(type, value, traceback);
}

void PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)¶

Part of the Stable ABI.

Deprecated since version 3.12: Use PyErr_SetRaisedException() instead.

Set the error indicator from the three objects, type, value, and traceback, clearing the existing exception if one is set. If the objects are NULL, the error indicator is cleared. Do not pass a NULL type and non-NULL value or traceback. The exception type should be a class. Do not pass an invalid exception type or value. (Violating these rules will cause subtle problems later.) This call takes away a reference to each object: you must own a reference to each object before the call and after the call you no longer own these references. (If you don’t understand this, don’t use this function. I warned you.)

Note

This function is normally only used by legacy code that needs to save and restore the error indicator temporarily. Use PyErr_Fetch() to save the current error indicator.

void PyErr_NormalizeException(PyObject **exc, PyObject **val, PyObject **tb)¶

Part of the Stable ABI.

Deprecated since version 3.12: Use PyErr_GetRaisedException() instead, to avoid any possible de-normalization.

Under certain circumstances, the values returned by PyErr_Fetch() below can be “unnormalized”, meaning that *exc is a class object but *val is not an instance of the same class. This function can be used to instantiate the class in that case. If the values are already normalized, nothing happens. The delayed normalization is implemented to improve performance.

Note

This function does not implicitly set the __traceback__ attribute on the exception value. If setting the traceback appropriately is desired, the following additional snippet is needed:

if (tb != NULL) {
  PyException_SetTraceback(val, tb);
}

PyObject *PyErr_GetHandledException(void)¶

Part of the Stable ABI since version 3.11.

Retrieve the active exception instance, as would be returned by sys.exception(). This refers to an exception that was already caught, not to an exception that was freshly raised. Returns a new reference to the exception or NULL. Does not modify the interpreter’s exception state.

Note

This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_SetHandledException() to restore or clear the exception state.

Added in version 3.11.

void PyErr_SetHandledException(PyObject *exc)¶

Part of the Stable ABI since version 3.11.

Set the active exception, as known from sys.exception(). This refers to an exception that was already caught, not to an exception that was freshly raised. To clear the exception state, pass NULL.

Note

This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_GetHandledException() to get the exception state.

Added in version 3.11.

void PyErr_GetExcInfo(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)¶

Part of the Stable ABI since version 3.7.

Retrieve the old-style representation of the exception info, as known from sys.exc_info(). This refers to an exception that was already caught, not to an exception that was freshly raised. Returns new references for the three objects, any of which may be NULL. Does not modify the exception info state. This function is kept for backwards compatibility. Prefer using PyErr_GetHandledException().

Note

This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_SetExcInfo() to restore or clear the exception state.

Added in version 3.3.

void PyErr_SetExcInfo(PyObject *type, PyObject *value, PyObject *traceback)¶

Part of the Stable ABI since version 3.7.

Set the exception info, as known from sys.exc_info(). This refers to an exception that was already caught, not to an exception that was freshly raised. This function “steals” the references of the arguments. To clear the exception state, pass NULL for all three arguments. This function is kept for backwards compatibility. Prefer using PyErr_SetHandledException().

Note

This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_GetExcInfo() to read the exception state.

Added in version 3.3.

Changed in version 3.11: The type and traceback arguments are no longer used and can be NULL. The interpreter now derives them from the exception instance (the value argument). The function still “steals” references of all three arguments.

Signal Handling¶

int PyErr_CheckSignals()¶

Part of the Stable ABI.

Handle external interruptions, such as signals or activating a debugger, whose processing has been delayed until it is safe to run Python code and/or raise exceptions.

For example, pressing Ctrl-C causes a terminal to send the signal.SIGINT signal. This function executes the corresponding Python signal handler, which, by default, raises the KeyboardInterrupt exception.

PyErr_CheckSignals() should be called by long-running C code frequently enough so that the response appears immediate to humans.

Handlers invoked by this function currently include:

• Signal handlers, including Python functions registered using the signal module.

  Signal handlers are only run in the main thread of the main interpreter.

  (This is where the function got the name: originally, signals were the only way to interrupt the interpreter.)

• Running the garbage collector, if necessary.

• Executing a pending remote debugger script.

• Raise the exception set by PyThreadState_SetAsyncExc().

If any handler raises an exception, immediately return -1 with that exception set. Any remaining interruptions are left to be processed on the next PyErr_CheckSignals() invocation, if appropriate.

If all handlers finish successfully, or there are no handlers to run, return 0.

Changed in version 3.12: This function may now invoke the garbage collector.

Changed in version 3.14: This function may now execute a remote debugger script, if remote debugging is enabled.

Changed in version 3.15: The exception set by PyThreadState_SetAsyncExc() is now raised.

void PyErr_SetInterrupt()¶

Part of the Stable ABI.

Simulate the effect of a SIGINT signal arriving. This is equivalent to PyErr_SetInterruptEx(SIGINT).

Note

This function is async-signal-safe. It can be called without an attached thread state and from a C signal handler.

int PyErr_SetInterruptEx(int signum)¶

Part of the Stable ABI since version 3.10.

Simulate the effect of a signal arriving. The next time PyErr_CheckSignals() is called, the Python signal handler for the given signal number will be called.

This function can be called by C code that sets up its own signal handling and wants Python signal handlers to be invoked as expected when an interruption is requested (for example when the user presses Ctrl-C to interrupt an operation).

If the given signal isn’t handled by Python (it was set to signal.SIG_DFL or signal.SIG_IGN), it will be ignored.

If signum is outside of the allowed range of signal numbers, -1 is returned. Otherwise, 0 is returned. The error indicator is never changed by this function.

Note

This function is async-signal-safe. It can be called without an attached thread state and from a C signal handler.

Added in version 3.10.

int PySignal_SetWakeupFd(int fd)¶

This utility function specifies a file descriptor to which the signal number is written as a single byte whenever a signal is received. fd must be non-blocking. It returns the previous such file descriptor.

The value -1 disables the feature; this is the initial state. This is equivalent to signal.set_wakeup_fd() in Python, but without any error checking. fd should be a valid file descriptor. The function should only be called from the main thread.

Changed in version 3.5: On Windows, the function now also supports socket handles.

Exception Classes¶

PyObject *PyErr_NewException(const char *name, PyObject *base, PyObject *dict)¶

Return value: New reference. Part of the Stable ABI.

This utility function creates and returns a new exception class. The name argument must be the name of the new exception, a C string of the form module.classname. The base and dict arguments are normally NULL. This creates a class object derived from Exception (accessible in C as PyExc_Exception).

The __module__ attribute of the new class is set to the first part (up to the last dot) of the name argument, and the class name is set to the last part (after the last dot). The base argument can be used to specify alternate base classes; it can either be only one class or a tuple of classes. The dict argument can be used to specify a dictionary of class variables and methods.

PyObject *PyErr_NewExceptionWithDoc(const char *name, const char *doc, PyObject *base, PyObject *dict)¶

Return value: New reference. Part of the Stable ABI.

Same as PyErr_NewException(), except that the new exception class can easily be given a docstring: If doc is non-NULL, it will be used as the docstring for the exception class.

Added in version 3.2.

int PyExceptionClass_Check(PyObject *ob)¶

Return non-zero if ob is an exception class, zero otherwise. This function always succeeds.

const char *PyExceptionClass_Name(PyObject *ob)¶

Part of the Stable ABI since version 3.8.

Return tp_name of the exception class ob.

PyException_HEAD¶

This is a macro including the base fields for an exception object.

This was included in Python’s C API by mistake and is not designed for use in extensions. For creating custom exception objects, use PyErr_NewException() or otherwise create a class inheriting from PyExc_BaseException.

Soft deprecated since version 3.15.

Exception Objects¶

int PyExceptionInstance_Check(PyObject *op)¶

Return true if op is an instance of BaseException, false otherwise. This function always succeeds.

PyExceptionInstance_Class(op)¶

Equivalent to Py_TYPE(op).

PyObject *PyException_GetTraceback(PyObject *ex)¶

Return value: New reference. Part of the Stable ABI.

Return the traceback associated with the exception as a new reference, as accessible from Python through the __traceback__ attribute. If there is no traceback associated, this returns NULL.

int PyException_SetTraceback(PyObject *ex, PyObject *tb)¶

Part of the Stable ABI.

Set the traceback associated with the exception to tb. Use Py_None to clear it.

PyObject *PyException_GetContext(PyObject *ex)¶

Return value: New reference. Part of the Stable ABI.

Return the context (another exception instance during whose handling ex was raised) associated with the exception as a new reference, as accessible from Python through the __context__ attribute. If there is no context associated, this returns NULL.

void PyException_SetContext(PyObject *ex, PyObject *ctx)¶

Part of the Stable ABI.

Set the context associated with the exception to ctx. Use NULL to clear it. There is no type check to make sure that ctx is an exception instance. This “steals” a reference to ctx.

PyObject *PyException_GetCause(PyObject *ex)¶

Return value: New reference. Part of the Stable ABI.

Return the cause (either an exception instance, or None, set by raise ... from ...) associated with the exception as a new reference, as accessible from Python through the __cause__ attribute.

void PyException_SetCause(PyObject *ex, PyObject *cause)¶

Part of the Stable ABI.

Set the cause associated with the exception to cause. Use NULL to clear it. There is no type check to make sure that cause is either an exception instance or None. This “steals” a reference to cause.

The __suppress_context__ attribute is implicitly set to True by this function.

PyObject *PyException_GetArgs(PyObject *ex)¶

Return value: New reference. Part of the Stable ABI since version 3.12.

Return args of exception ex.

void PyException_SetArgs(PyObject *ex, PyObject *args)¶

Part of the Stable ABI since version 3.12.

Set args of exception ex to args.

PyObject *PyUnstable_Exc_PrepReraiseStar(PyObject *orig, PyObject *excs)¶

This is Unstable API. It may change without warning in minor releases.

Implement part of the interpreter’s implementation of except*. orig is the original exception that was caught, and excs is the list of the exceptions that need to be raised. This list contains the unhandled part of orig, if any, as well as the exceptions that were raised from the except* clauses (so they have a different traceback from orig) and those that were reraised (and have the same traceback as orig). Return the ExceptionGroup that needs to be reraised in the end, or None if there is nothing to reraise.

Added in version 3.12.

Unicode Exception Objects¶

The following functions are used to create and modify Unicode exceptions from C.

PyObject *PyUnicodeDecodeError_Create(const char *encoding, const char *object, Py_ssize_t length, Py_ssize_t start, Py_ssize_t end, const char *reason)¶

Return value: New reference. Part of the Stable ABI.

Create a UnicodeDecodeError object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.

PyObject *PyUnicodeDecodeError_GetEncoding(PyObject *exc)¶

PyObject *PyUnicodeEncodeError_GetEncoding(PyObject *exc)¶

Return value: New reference. Part of the Stable ABI.

Return the encoding attribute of the given exception object.

PyObject *PyUnicodeDecodeError_GetObject(PyObject *exc)¶

PyObject *PyUnicodeEncodeError_GetObject(PyObject *exc)¶

PyObject *PyUnicodeTranslateError_GetObject(PyObject *exc)¶

Return value: New reference. Part of the Stable ABI.

Return the object attribute of the given exception object.

int PyUnicodeDecodeError_GetStart(PyObject *exc, Py_ssize_t *start)¶

int PyUnicodeEncodeError_GetStart(PyObject *exc, Py_ssize_t *start)¶

int PyUnicodeTranslateError_GetStart(PyObject *exc, Py_ssize_t *start)¶

Part of the Stable ABI.

Get the start attribute of the given exception object and place it into *start. start must not be NULL. Return 0 on success, -1 on failure.

If the UnicodeError.object is an empty sequence, the resulting start is 0. Otherwise, it is clipped to [0, len(object) - 1].

See also

UnicodeError.start

int PyUnicodeDecodeError_SetStart(PyObject *exc, Py_ssize_t start)¶

int PyUnicodeEncodeError_SetStart(PyObject *exc, Py_ssize_t start)¶

int PyUnicodeTranslateError_SetStart(PyObject *exc, Py_ssize_t start)¶

Part of the Stable ABI.

Set the start attribute of the given exception object to start. Return 0 on success, -1 on failure.

Note

While passing a negative start does not raise an exception, the corresponding getters will not consider it as a relative offset.

int PyUnicodeDecodeError_GetEnd(PyObject *exc, Py_ssize_t *end)¶

int PyUnicodeEncodeError_GetEnd(PyObject *exc, Py_ssize_t *end)¶

int PyUnicodeTranslateError_GetEnd(PyObject *exc, Py_ssize_t *end)¶

Part of the Stable ABI.

Get the end attribute of the given exception object and place it into *end. end must not be NULL. Return 0 on success, -1 on failure.

If the UnicodeError.object is an empty sequence, the resulting end is 0. Otherwise, it is clipped to [1, len(object)].

int PyUnicodeDecodeError_SetEnd(PyObject *exc, Py_ssize_t end)¶

int PyUnicodeEncodeError_SetEnd(PyObject *exc, Py_ssize_t end)¶

int PyUnicodeTranslateError_SetEnd(PyObject *exc, Py_ssize_t end)¶

Part of the Stable ABI.

Set the end attribute of the given exception object to end. Return 0 on success, -1 on failure.

See also

UnicodeError.end

PyObject *PyUnicodeDecodeError_GetReason(PyObject *exc)¶

PyObject *PyUnicodeEncodeError_GetReason(PyObject *exc)¶

PyObject *PyUnicodeTranslateError_GetReason(PyObject *exc)¶

Return value: New reference. Part of the Stable ABI.

Return the reason attribute of the given exception object.

int PyUnicodeDecodeError_SetReason(PyObject *exc, const char *reason)¶

int PyUnicodeEncodeError_SetReason(PyObject *exc, const char *reason)¶

int PyUnicodeTranslateError_SetReason(PyObject *exc, const char *reason)¶

Part of the Stable ABI.

Set the reason attribute of the given exception object to reason. Return 0 on success, -1 on failure.

Recursion Control¶

These two functions provide a way to perform safe recursive calls at the C level, both in the core and in extension modules. They are needed if the recursive code does not necessarily invoke Python code (which tracks its recursion depth automatically). They are also not needed for tp_call implementations because the call protocol takes care of recursion handling.

int Py_EnterRecursiveCall(const char *where)¶

Part of the Stable ABI since version 3.9.

Marks a point where a recursive C-level call is about to be performed.

The function then checks if the stack limit is reached. If this is the case, a RecursionError is set and a nonzero value is returned. Otherwise, zero is returned.

The check is based on the remaining C stack space of the current thread, not on a count of calls, so it is unaffected by Py_SetRecursionLimit() and sys.setrecursionlimit().

where should be a UTF-8 encoded string such as " in instance check" to be concatenated to the RecursionError message caused by the recursion depth limit.

See also

The PyUnstable_ThreadState_SetStackProtection() function.

Changed in version 3.9: This function is now also available in the limited API.

Changed in version 3.14: The check is based on the remaining C stack space. Previously, a separate counter of C-level calls was used.

void Py_LeaveRecursiveCall(void)¶

Part of the Stable ABI since version 3.9.

Ends a Py_EnterRecursiveCall(). Must be called once for each successful invocation of Py_EnterRecursiveCall().

Changed in version 3.9: This function is now also available in the limited API.

Properly implementing tp_repr for container types requires special recursion handling. In addition to protecting the stack, tp_repr also needs to track objects to prevent cycles. The following two functions facilitate this functionality. Effectively, these are the C equivalent to @reprlib.recursive_repr.

int Py_ReprEnter(PyObject *object)¶

Part of the Stable ABI.

Called at the beginning of the tp_repr implementation to detect cycles.

If the object has already been processed, the function returns a positive integer. In that case the tp_repr implementation should return a string object indicating a cycle. As examples, dict objects return {...} and list objects return [...].

The function will return a negative integer if the recursion limit is reached. In that case the tp_repr implementation should typically return NULL.

Otherwise, the function returns zero and the tp_repr implementation can continue normally.

void Py_ReprLeave(PyObject *object)¶

Part of the Stable ABI.

Ends a Py_ReprEnter(). Must be called once for each invocation of Py_ReprEnter() that returns zero.

int Py_GetRecursionLimit(void)¶

Part of the Stable ABI.

Get the recursion limit for the current interpreter. It can be set with Py_SetRecursionLimit(). The recursion limit prevents the Python interpreter stack from growing infinitely.

This function cannot fail, and the caller must hold an attached thread state.

See also

sys.getrecursionlimit()

void Py_SetRecursionLimit(int new_limit)¶

Part of the Stable ABI.

Set the recursion limit for the current interpreter.

This function cannot fail, and the caller must hold an attached thread state.

See also

sys.setrecursionlimit()

Exception and warning types¶

All standard Python exceptions and warning categories are available as global variables whose names are PyExc_ followed by the Python exception name. These have the type PyObject*; they are all class objects.

For completeness, here are all the variables:

Tracebacks¶

PyTypeObject PyTraceBack_Type¶

Part of the Stable ABI.

Type object for traceback objects. This is available as types.TracebackType in the Python layer.

int PyTraceBack_Check(PyObject *op)¶

Return true if op is a traceback object, false otherwise. This function does not account for subtypes.

int PyTraceBack_Here(PyFrameObject *f)¶

Part of the Stable ABI.

Replace the __traceback__ attribute on the current exception with a new traceback prepending f to the existing chain.

Calling this function without an exception set is undefined behavior.

This function returns 0 on success, and returns -1 with an exception set on failure.

int PyTraceBack_Print(PyObject *tb, PyObject *f)¶

Part of the Stable ABI.

Write the traceback tb into the file f.

This function returns 0 on success, and returns -1 with an exception set on failure.

const char *PyUnstable_DumpTraceback(int fd, PyThreadState *tstate)¶

This is Unstable API. It may change without warning in minor releases.

Write a trace of the Python stack in tstate into the file fd. The format looks like:

Traceback (most recent call first):
  File "xxx", line xxx in <xxx>
  File "xxx", line xxx in <xxx>
  ...
  File "xxx", line xxx in <xxx>

This function is meant to debug situations such as segfaults, fatal errors, and similar. The file and function names it outputs are encoded to ASCII with backslashreplace and truncated to 500 characters. It writes only the first 100 frames; further frames are truncated with the line ....

This function will return NULL on success, or an error message on error.

This function is intended for use in crash scenarios such as signal handlers for SIGSEGV, where the interpreter may be in an inconsistent state. Given that it reads interpreter data structures that may be partially modified, the function might produce incomplete output or it may even crash itself.

The caller does not need to hold an attached thread state, nor does tstate need to be attached.

Added in version 3.15.

const char *PyUnstable_DumpTracebackThreads(int fd, PyInterpreterState *interp, PyThreadState *current_tstate, Py_ssize_t max_threads)¶

This is Unstable API. It may change without warning in minor releases.

Write the traces of all Python threads in interp into the file fd.

If interp is NULL then this function will try to identify the current interpreter using thread-specific storage. If it cannot, it will return an error.

If current_tstate is not NULL then it will be used to identify what the current thread is in the written output. If it is NULL then this function will identify the current thread using thread-specific storage. It is not an error if the function is unable to get the current Python thread state.

This function will return NULL on success, or an error message on error.

This function is meant to debug situations such as segfaults, fatal errors, and similar. It calls PyUnstable_DumpTraceback() for each thread. It only writes the tracebacks of the first max_threads threads, further output is truncated with the line .... If max_threads is 0, the function will use a default value of 100 for the argument.

This function is intended for use in crash scenarios such as signal handlers for SIGSEGV, where the interpreter may be in an inconsistent state. Given that it reads interpreter data structures that may be partially modified, the function might produce incomplete output or it may even crash itself.

The caller does not need to hold an attached thread state, nor does current_tstate need to be attached.

Warning

On the free-threaded build, this function is not thread-safe. If another thread deletes its thread state while this function is being called, the process will likely crash.

Added in version 3.15.