Doc/c-api/exceptions.rst
.. highlight:: c
.. _exceptionhandling:
Exception Handling
The functions described in this chapter will let you handle and raise Python
exceptions. It is important to understand some of the basics of Python
exception handling. It works somewhat like the POSIX :c:data:errno variable:
there is a global indicator (per thread) of the last error that occurred. Most
C API functions don't clear this on success, but will set it to indicate the
cause of the error on failure. Most C API functions also return an error
indicator, usually NULL if they are supposed to return a pointer, or -1
if they return an integer (exception: the PyArg_* functions
return 1 for success and 0 for failure).
Concretely, the error indicator consists of three object pointers: the
exception's type, the exception's value, and the traceback object. Any
of those pointers can be NULL if non-set (although some combinations are
forbidden, for example you can't have a non-NULL traceback if the exception
type is NULL).
When a function must fail because some function it called failed, it generally doesn't set the error indicator; the function it called already set it. It is responsible for either handling the error and clearing the exception or returning after cleaning up any resources it holds (such as object references or memory allocations); it should not continue normally if it is not prepared to handle the error. If returning due to an error, it is important to indicate to the caller that an error has been set. If the error is not handled or carefully propagated, additional calls into the Python/C API may not behave as intended and may fail in mysterious ways.
.. note::
The error indicator is not the result of :func:sys.exc_info.
The former corresponds to an exception that is not yet caught (and is
therefore still propagating), while the latter returns an exception after
it is caught (and has therefore stopped propagating).
.. c:function:: void PyErr_Clear()
Clear the error indicator. If the error indicator is not set, there is no effect.
.. c:function:: void PyErr_PrintEx(int set_sys_last_vars)
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 :data:sys.last_exc is
set to the printed exception. For backwards compatibility, the
deprecated variables :data:sys.last_type, :data:sys.last_value and
:data:sys.last_traceback are also set to the type, value and traceback
of this exception, respectively.
.. versionchanged:: 3.12
The setting of :data:sys.last_exc was added.
.. c:function:: void PyErr_Print()
Alias for PyErr_PrintEx(1).
.. c:function:: void PyErr_WriteUnraisable(PyObject *obj)
Call :func: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
:meth:~object.__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.
.. versionchanged:: 3.4
Print a traceback. Print only traceback if obj is NULL.
.. versionchanged:: 3.8
Use :func:sys.unraisablehook.
.. c:function:: void PyErr_FormatUnraisable(const char *format, ...)
Similar to :c:func:PyErr_WriteUnraisable, but the format and subsequent
parameters help format the warning message; they have the same meaning and
values as in :c:func: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.
.. versionadded:: 3.13
.. c:function:: void PyErr_DisplayException(PyObject *exc)
Print the standard traceback display of exc to sys.stderr, including
chained exceptions and notes.
.. versionadded:: 3.12
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.
.. c:function:: void PyErr_SetString(PyObject *type, const char *message)
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. :c:data:PyExc_RuntimeError. You need not create a new
:term:strong reference to it (e.g. with :c:func:Py_INCREF).
The second argument is an error message; it is decoded from 'utf-8'.
.. c:function:: void PyErr_SetObject(PyObject *type, PyObject *value)
This function is similar to :c:func:PyErr_SetString but lets you specify an
arbitrary Python object for the "value" of the exception.
.. c:function:: PyObject* PyErr_Format(PyObject *exception, const char *format, ...)
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 :c:func:PyUnicode_FromFormat. format is an ASCII-encoded
string.
.. c:function:: PyObject* PyErr_FormatV(PyObject *exception, const char *format, va_list vargs)
Same as :c:func:PyErr_Format, but taking a :c:type:va_list argument rather
than a variable number of arguments.
.. versionadded:: 3.5
.. c:function:: void PyErr_SetNone(PyObject *type)
This is a shorthand for PyErr_SetObject(type, Py_None).
.. c:function:: int PyErr_BadArgument()
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.
.. c:function:: PyObject* PyErr_NoMemory()
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.
.. c:function:: PyObject* PyErr_SetFromErrno(PyObject *type)
.. index:: single: strerror (C function)
This is a convenience function to raise an exception when a C library function
has returned an error and set the C variable :c:data:errno. It constructs a
tuple object whose first item is the integer :c:data:errno value and whose
second item is the corresponding error message (gotten from :c:func:!strerror),
and then calls PyErr_SetObject(type, object). On Unix, when the
:c:data:errno value is :c:macro:!EINTR, indicating an interrupted system call,
this calls :c:func: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.
.. c:function:: PyObject* PyErr_SetFromErrnoWithFilenameObject(PyObject *type, PyObject *filenameObject)
Similar to :c:func: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 :exc:OSError exception,
this is used to define the :attr:!filename attribute of the
exception instance.
.. c:function:: PyObject* PyErr_SetFromErrnoWithFilenameObjects(PyObject *type, PyObject *filenameObject, PyObject *filenameObject2)
Similar to :c:func:PyErr_SetFromErrnoWithFilenameObject, but takes a second
filename object, for raising errors when a function that takes two filenames
fails.
.. versionadded:: 3.4
.. c:function:: PyObject* PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)
Similar to :c:func:PyErr_SetFromErrnoWithFilenameObject, but the filename
is given as a C string. filename is decoded from the :term:filesystem encoding and error handler.
.. c:function:: PyObject* PyErr_SetFromWindowsErr(int ierr)
This is a convenience function to raise :exc:OSError. If called with
ierr of 0, the error code returned by a call to :c:func:!GetLastError
is used instead. It calls the Win32 function :c:func:!FormatMessage to retrieve
the Windows description of error code given by ierr or :c:func:!GetLastError,
then it constructs a :exc:OSError object with the :attr:~OSError.winerror
attribute set to the error code, the :attr:~OSError.strerror attribute
set to the corresponding error message (gotten from
:c:func:!FormatMessage), and then calls PyErr_SetObject(PyExc_OSError, object). This function always returns NULL.
.. availability:: Windows.
.. c:function:: PyObject* PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)
Similar to :c:func:PyErr_SetFromWindowsErr, with an additional parameter
specifying the exception type to be raised.
.. availability:: Windows.
.. c:function:: PyObject* PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)
Similar to :c:func:PyErr_SetFromWindowsErr, with the additional behavior
that if filename is not NULL, it is decoded from the filesystem
encoding (:func:os.fsdecode) and passed to the constructor of
:exc:OSError as a third parameter to be used to define the
:attr:!filename attribute of the exception instance.
.. availability:: Windows.
.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObject(PyObject *type, int ierr, PyObject *filename)
Similar to :c:func:PyErr_SetExcFromWindowsErr, with the additional behavior
that if filename is not NULL, it is passed to the constructor of
:exc:OSError as a third parameter to be used to define the
:attr:!filename attribute of the exception instance.
.. availability:: Windows.
.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObjects(PyObject *type, int ierr, PyObject *filename, PyObject *filename2)
Similar to :c:func:PyErr_SetExcFromWindowsErrWithFilenameObject,
but accepts a second filename object.
.. availability:: Windows.
.. versionadded:: 3.4
.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, const char *filename)
Similar to :c:func:PyErr_SetFromWindowsErrWithFilename, with an additional
parameter specifying the exception type to be raised.
.. availability:: Windows.
.. c:function:: PyObject* PyErr_SetImportError(PyObject *msg, PyObject *name, PyObject *path)
This is a convenience function to raise :exc: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 :exc:ImportError's respective name
and path attributes.
.. versionadded:: 3.3
.. c:function:: PyObject* PyErr_SetImportErrorSubclass(PyObject *exception, PyObject *msg, PyObject *name, PyObject *path)
Much like :c:func:PyErr_SetImportError but this function allows for
specifying a subclass of :exc:ImportError to raise.
.. versionadded:: 3.6
.. c:function:: 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 :exc:SyntaxError, then it sets additional
attributes, which make the exception printing subsystem think the exception
is a :exc:SyntaxError.
.. versionadded:: 3.4
.. c:function:: void PyErr_RangedSyntaxLocationObject(PyObject *filename, int lineno, int col_offset, int end_lineno, int end_col_offset)
Similar to :c:func:PyErr_SyntaxLocationObject, but also sets the
end_lineno and end_col_offset information for the current exception.
.. versionadded:: 3.10
.. c:function:: void PyErr_SyntaxLocationEx(const char *filename, int lineno, int col_offset)
Like :c:func:PyErr_SyntaxLocationObject, but filename is a byte string
decoded from the :term:filesystem encoding and error handler.
.. versionadded:: 3.2
.. c:function:: void PyErr_SyntaxLocation(const char *filename, int lineno)
Like :c:func:PyErr_SyntaxLocationEx, but the col_offset parameter is
omitted.
.. c:function:: void PyErr_BadInternalCall()
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.
.. c:function:: PyObject *PyErr_ProgramTextObject(PyObject *filename, int lineno)
Get the source line in filename at line lineno. filename should be a
Python :class: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.
.. c:function:: PyObject *PyErr_ProgramText(const char *filename, int lineno)
Similar to :c:func:PyErr_ProgramTextObject, but filename is a
:c:expr:const char *, which is decoded with the
:term:filesystem encoding and error handler, instead of a
Python object reference.
Use these functions to issue warnings from C code. They mirror similar
functions exported by the Python :mod: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, :c:func:Py_DECREF owned references and return
an error value).
.. c:function:: int PyErr_WarnEx(PyObject *category, const char *message, Py_ssize_t stack_level)
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 :c:func:PyErr_WarnEx, 2 is the function above that,
and so forth.
Warning categories must be subclasses of :c:data:PyExc_Warning;
:c:data:PyExc_Warning is a subclass of :c:data:PyExc_Exception;
the default warning category is :c:data:PyExc_RuntimeWarning. The standard
Python warning categories are available as global variables whose names are
enumerated at :ref:standardwarningcategories.
For information about warning control, see the documentation for the
:mod:warnings module and the :option:-W option in the command line
documentation. There is no C API for warning control.
.. c:function:: 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
:func: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.
.. versionadded:: 3.4
.. c:function:: int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)
Similar to :c:func:PyErr_WarnExplicitObject except that message and
module are UTF-8 encoded strings, and filename is decoded from the
:term:filesystem encoding and error handler.
.. c:function:: int PyErr_WarnFormat(PyObject *category, Py_ssize_t stack_level, const char *format, ...)
Function similar to :c:func:PyErr_WarnEx, but use
:c:func:PyUnicode_FromFormat to format the warning message. format is
an ASCII-encoded string.
.. versionadded:: 3.2
.. c:function:: int PyErr_WarnExplicitFormat(PyObject *category, const char *filename, int lineno, const char *module, PyObject *registry, const char *format, ...)
Similar to :c:func:PyErr_WarnExplicit, but uses
:c:func:PyUnicode_FromFormat to format the warning message. format is
an ASCII-encoded string.
.. versionadded:: 3.2
.. c:function:: int PyErr_ResourceWarning(PyObject *source, Py_ssize_t stack_level, const char *format, ...)
Function similar to :c:func:PyErr_WarnFormat, but category is
:exc:ResourceWarning and it passes source to :class:!warnings.WarningMessage.
.. versionadded:: 3.6
.. c:function:: PyObject* PyErr_Occurred()
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 :c:func:PyErr_Restore). If not set, return NULL. You do not
own a reference to the return value, so you do not need to :c:func:Py_DECREF
it.
The caller must have an :term:attached thread state.
.. note::
Do not compare the return value to a specific exception; use
:c:func:`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.)
.. c:function:: int PyErr_ExceptionMatches(PyObject *exc)
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.
.. c:function:: int PyErr_GivenExceptionMatches(PyObject *given, PyObject *exc)
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.
.. c:function:: PyObject *PyErr_GetRaisedException(void)
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);
}
.. seealso:: :c:func:PyErr_GetHandledException,
to save the exception currently being handled.
.. versionadded:: 3.12
.. c:function:: void PyErr_SetRaisedException(PyObject *exc)
Set exc as the exception currently being raised, clearing the existing exception if one is set.
.. warning::
This call steals a reference to *exc*, which must be a valid exception.
.. versionadded:: 3.12
.. c:function:: void PyErr_Fetch(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
.. deprecated:: 3.12
Use :c:func:`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);
}
.. c:function:: void PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)
.. deprecated:: 3.12
Use :c:func:`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 :c:func:`PyErr_Fetch` to save the current error indicator.
.. c:function:: void PyErr_NormalizeException(PyObject **exc, PyObject **val, PyObject **tb)
.. deprecated:: 3.12
Use :c:func:`PyErr_GetRaisedException` instead,
to avoid any possible de-normalization.
Under certain circumstances, the values returned by :c:func: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
:attr:`~BaseException.__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);
}
.. c:function:: PyObject* PyErr_GetHandledException(void)
Retrieve the active exception instance, as would be returned by :func: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 :c:func:`PyErr_SetHandledException` to restore or
clear the exception state.
.. versionadded:: 3.11
.. c:function:: void PyErr_SetHandledException(PyObject *exc)
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 :c:func:`PyErr_GetHandledException` to get the exception
state.
.. versionadded:: 3.11
.. c:function:: void PyErr_GetExcInfo(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
Retrieve the old-style representation of the exception info, as known from
:func: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
:c:func: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 :c:func:`PyErr_SetExcInfo` to restore or clear the
exception state.
.. versionadded:: 3.3
.. c:function:: void PyErr_SetExcInfo(PyObject *type, PyObject *value, PyObject *traceback)
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
:c:func: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 :c:func:`PyErr_GetExcInfo` to read the exception
state.
.. versionadded:: 3.3
.. versionchanged:: 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.
.. c:function:: int PyErr_CheckSignals()
.. index:: pair: module; signal single: SIGINT (C macro) single: KeyboardInterrupt (built-in exception)
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 :kbd:Ctrl-C causes a terminal to send the
:py:data:signal.SIGINT signal.
This function executes the corresponding Python signal handler, which,
by default, raises the :exc:KeyboardInterrupt exception.
:c:func:!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 :mod: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 :ref:remote debugger <remote-debugging> script.
Raise the exception set by :c:func: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
:c:func:PyErr_CheckSignals() invocation, if appropriate.
If all handlers finish successfully, or there are no handlers to run,
return 0.
.. versionchanged:: 3.12 This function may now invoke the garbage collector.
.. versionchanged:: 3.14 This function may now execute a remote debugger script, if remote debugging is enabled.
.. versionchanged:: 3.15
The exception set by :c:func:PyThreadState_SetAsyncExc is now raised.
.. c:function:: void PyErr_SetInterrupt()
.. index:: pair: module; signal single: SIGINT (C macro) single: KeyboardInterrupt (built-in exception)
Simulate the effect of a :c:macro:!SIGINT signal arriving.
This is equivalent to PyErr_SetInterruptEx(SIGINT).
.. note::
This function is async-signal-safe. It can be called without
an :term:attached thread state and from a C signal handler.
.. c:function:: int PyErr_SetInterruptEx(int signum)
.. index:: pair: module; signal single: KeyboardInterrupt (built-in exception)
Simulate the effect of a signal arriving. The next time
:c:func: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
:py:const:signal.SIG_DFL or :py:const: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 :term:attached thread state and from a C signal handler.
.. versionadded:: 3.10
.. c:function:: 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 :func: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.
.. versionchanged:: 3.5 On Windows, the function now also supports socket handles.
.. c:function:: PyObject* PyErr_NewException(const char *name, PyObject *base, PyObject *dict)
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 :exc:Exception (accessible in C as
:c:data:PyExc_Exception).
The :attr:~type.__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.
.. c:function:: PyObject* PyErr_NewExceptionWithDoc(const char *name, const char *doc, PyObject *base, PyObject *dict)
Same as :c:func: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.
.. versionadded:: 3.2
.. c:function:: int PyExceptionClass_Check(PyObject *ob)
Return non-zero if ob is an exception class, zero otherwise. This function always succeeds.
.. c:function:: const char *PyExceptionClass_Name(PyObject *ob)
Return :c:member:~PyTypeObject.tp_name of the exception class ob.
.. c:macro:: PyException_HEAD
This is a :term:soft deprecated 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
:c:func:PyErr_NewException or otherwise create a class inheriting from
:c:data:PyExc_BaseException.
.. c:function:: int PyExceptionInstance_Check(PyObject *op)
Return true if op is an instance of :class:BaseException, false
otherwise. This function always succeeds.
.. c:macro:: PyExceptionInstance_Class(op)
Equivalent to :c:func:Py_TYPE(op) <Py_TYPE>.
.. c:function:: PyObject* PyException_GetTraceback(PyObject *ex)
Return the traceback associated with the exception as a new reference, as
accessible from Python through the :attr:~BaseException.__traceback__
attribute. If there is no
traceback associated, this returns NULL.
.. c:function:: int PyException_SetTraceback(PyObject *ex, PyObject *tb)
Set the traceback associated with the exception to tb. Use Py_None to
clear it.
.. c:function:: PyObject* PyException_GetContext(PyObject *ex)
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 :attr:~BaseException.__context__ attribute.
If there is no context associated, this returns NULL.
.. c:function:: void PyException_SetContext(PyObject *ex, PyObject *ctx)
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.
.. c:function:: PyObject* PyException_GetCause(PyObject *ex)
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
:attr:~BaseException.__cause__ attribute.
.. c:function:: void PyException_SetCause(PyObject *ex, PyObject *cause)
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 :attr:~BaseException.__suppress_context__ attribute is implicitly set
to True by this function.
.. c:function:: PyObject* PyException_GetArgs(PyObject *ex)
Return :attr:~BaseException.args of exception ex.
.. c:function:: void PyException_SetArgs(PyObject *ex, PyObject *args)
Set :attr:~BaseException.args of exception ex to args.
.. c:function:: PyObject* PyUnstable_Exc_PrepReraiseStar(PyObject *orig, PyObject *excs)
Implement part of the interpreter's implementation of :keyword:!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
:keyword:!except* clauses (so they have a different traceback from orig) and
those that were reraised (and have the same traceback as orig).
Return the :exc:ExceptionGroup that needs to be reraised in the end, or
None if there is nothing to reraise.
.. versionadded:: 3.12
.. _unicodeexceptions:
The following functions are used to create and modify Unicode exceptions from C.
.. c:function:: PyObject* PyUnicodeDecodeError_Create(const char *encoding, const char *object, Py_ssize_t length, Py_ssize_t start, Py_ssize_t end, const char *reason)
Create a :class:UnicodeDecodeError object with the attributes encoding,
object, length, start, end and reason. encoding and reason are
UTF-8 encoded strings.
.. c:function:: PyObject* PyUnicodeDecodeError_GetEncoding(PyObject exc) PyObject PyUnicodeEncodeError_GetEncoding(PyObject *exc)
Return the encoding attribute of the given exception object.
.. c:function:: PyObject* PyUnicodeDecodeError_GetObject(PyObject exc) PyObject PyUnicodeEncodeError_GetObject(PyObject exc) PyObject PyUnicodeTranslateError_GetObject(PyObject *exc)
Return the object attribute of the given exception object.
.. c:function:: 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)
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 :attr:UnicodeError.object is an empty sequence, the resulting
start is 0. Otherwise, it is clipped to [0, len(object) - 1].
.. seealso:: :attr:UnicodeError.start
.. c:function:: 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)
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.
.. c:function:: 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)
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 :attr:UnicodeError.object is an empty sequence, the resulting
end is 0. Otherwise, it is clipped to [1, len(object)].
.. c:function:: 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)
Set the end attribute of the given exception object to end. Return 0
on success, -1 on failure.
.. seealso:: :attr:UnicodeError.end
.. c:function:: PyObject* PyUnicodeDecodeError_GetReason(PyObject exc) PyObject PyUnicodeEncodeError_GetReason(PyObject exc) PyObject PyUnicodeTranslateError_GetReason(PyObject *exc)
Return the reason attribute of the given exception object.
.. c:function:: int PyUnicodeDecodeError_SetReason(PyObject *exc, const char *reason) int PyUnicodeEncodeError_SetReason(PyObject *exc, const char *reason) int PyUnicodeTranslateError_SetReason(PyObject *exc, const char *reason)
Set the reason attribute of the given exception object to reason. Return
0 on success, -1 on failure.
.. _recursion:
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 :ref:call protocol <call> takes care of recursion handling.
.. c:function:: int Py_EnterRecursiveCall(const char *where)
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 :exc:RecursionError is set and a nonzero value is returned.
Otherwise, zero is returned.
where should be a UTF-8 encoded string such as " in instance check" to
be concatenated to the :exc:RecursionError message caused by the recursion
depth limit.
.. seealso::
The :c:func:PyUnstable_ThreadState_SetStackProtection function.
.. versionchanged:: 3.9
This function is now also available in the :ref:limited API <limited-c-api>.
.. c:function:: void Py_LeaveRecursiveCall(void)
Ends a :c:func:Py_EnterRecursiveCall. Must be called once for each
successful invocation of :c:func:Py_EnterRecursiveCall.
.. versionchanged:: 3.9
This function is now also available in the :ref:limited API <limited-c-api>.
Properly implementing :c:member:~PyTypeObject.tp_repr for container types requires
special recursion handling. In addition to protecting the stack,
:c:member:~PyTypeObject.tp_repr also needs to track objects to prevent cycles. The
following two functions facilitate this functionality. Effectively,
these are the C equivalent to :func:reprlib.recursive_repr.
.. c:function:: int Py_ReprEnter(PyObject *object)
Called at the beginning of the :c:member:~PyTypeObject.tp_repr implementation to
detect cycles.
If the object has already been processed, the function returns a
positive integer. In that case the :c:member:~PyTypeObject.tp_repr implementation
should return a string object indicating a cycle. As examples,
:class:dict objects return {...} and :class:list objects
return [...].
The function will return a negative integer if the recursion limit
is reached. In that case the :c:member:~PyTypeObject.tp_repr implementation should
typically return NULL.
Otherwise, the function returns zero and the :c:member:~PyTypeObject.tp_repr
implementation can continue normally.
.. c:function:: void Py_ReprLeave(PyObject *object)
Ends a :c:func:Py_ReprEnter. Must be called once for each
invocation of :c:func:Py_ReprEnter that returns zero.
.. c:function:: int Py_GetRecursionLimit(void)
Get the recursion limit for the current interpreter. It can be set with
:c:func:Py_SetRecursionLimit. The recursion limit prevents the
Python interpreter stack from growing infinitely.
This function cannot fail, and the caller must hold an
:term:attached thread state.
.. seealso::
:py:func:sys.getrecursionlimit
.. c:function:: void Py_SetRecursionLimit(int new_limit)
Set the recursion limit for the current interpreter.
This function cannot fail, and the caller must hold an
:term:attached thread state.
.. seealso::
:py:func:sys.setrecursionlimit
.. _standardexceptions:
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 :c:expr:PyObject*; they are all class objects.
For completeness, here are all the variables:
.. list-table:: :align: left :widths: auto :header-rows: 1
BaseExceptionBaseExceptionGroupExceptionArithmeticErrorAssertionErrorAttributeErrorBlockingIOErrorBrokenPipeErrorBufferErrorChildProcessErrorConnectionAbortedErrorConnectionErrorConnectionRefusedErrorConnectionResetErrorEOFErrorFileExistsErrorFileNotFoundErrorFloatingPointErrorGeneratorExitImportCycleErrorImportErrorIndentationErrorIndexErrorInterruptedErrorIsADirectoryErrorKeyErrorKeyboardInterruptLookupErrorMemoryErrorModuleNotFoundErrorNameErrorNotADirectoryErrorNotImplementedErrorOSErrorOverflowErrorPermissionErrorProcessLookupErrorPythonFinalizationErrorRecursionErrorReferenceErrorRuntimeErrorStopAsyncIterationStopIterationSyntaxErrorSystemErrorSystemExitTabErrorTimeoutErrorTypeErrorUnboundLocalErrorUnicodeDecodeErrorUnicodeEncodeErrorUnicodeErrorUnicodeTranslateErrorValueErrorZeroDivisionError.. versionadded:: 3.3
:c:data:PyExc_BlockingIOError, :c:data:PyExc_BrokenPipeError,
:c:data:PyExc_ChildProcessError, :c:data:PyExc_ConnectionError,
:c:data:PyExc_ConnectionAbortedError, :c:data:PyExc_ConnectionRefusedError,
:c:data:PyExc_ConnectionResetError, :c:data:PyExc_FileExistsError,
:c:data:PyExc_FileNotFoundError, :c:data:PyExc_InterruptedError,
:c:data:PyExc_IsADirectoryError, :c:data:PyExc_NotADirectoryError,
:c:data:PyExc_PermissionError, :c:data:PyExc_ProcessLookupError
and :c:data:PyExc_TimeoutError were introduced following :pep:3151.
.. versionadded:: 3.5
:c:data:PyExc_StopAsyncIteration and :c:data:PyExc_RecursionError.
.. versionadded:: 3.6
:c:data:PyExc_ModuleNotFoundError.
.. versionadded:: 3.11
:c:data:PyExc_BaseExceptionGroup.
The following are a compatibility aliases to :c:data:PyExc_OSError.
.. versionchanged:: 3.3 These aliases used to be separate exception types.
.. list-table:: :align: left :widths: auto :header-rows: 1
OSErrorOSErrorOSErrorNotes:
.. [win]
:c:var:!PyExc_WindowsError is only defined on Windows; protect code that
uses this by testing that the preprocessor macro MS_WINDOWS is defined.
.. _standardwarningcategories:
.. list-table:: :align: left :widths: auto :header-rows: 1
WarningBytesWarningDeprecationWarningEncodingWarningFutureWarningImportWarningPendingDeprecationWarningResourceWarningRuntimeWarningSyntaxWarningUnicodeWarningUserWarning.. versionadded:: 3.2
:c:data:PyExc_ResourceWarning.
.. versionadded:: 3.10
:c:data:PyExc_EncodingWarning.
.. c:var:: PyTypeObject PyTraceBack_Type
Type object for traceback objects. This is available as
:class:types.TracebackType in the Python layer.
.. c:function:: int PyTraceBack_Check(PyObject *op)
Return true if op is a traceback object, false otherwise. This function does not account for subtypes.
.. c:function:: int PyTraceBack_Here(PyFrameObject *f)
Replace the :attr:~BaseException.__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.
.. c:function:: int PyTraceBack_Print(PyObject *tb, PyObject *f)
Write the traceback tb into the file f.
This function returns 0 on success, and returns -1 with an
exception set on failure.