Exception Handling

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 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 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).
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 aSystemExit
, in that case no traceback is printed and the Python process will exit with the error code specified by theSystemExit
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 variablessys.last_type
,sys.last_value
andsys.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 inPyUnicode_FromFormat()
.PyErr_WriteUnraisable(obj)
is roughly equivalent toPyErr_FormatUnraisable("Exception ignored in: %R", obj)
. If format isNULL
, 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
tosys.stderr
, including chained exceptions and notes.Added in version 3.12.
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. withPy_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 inPyUnicode_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 ava_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 returnsNULL
so an object allocation function can writereturn 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 integererrno
value and whose second item is the corresponding error message (gotten fromstrerror()
), and then callsPyErr_SetObject(type, object)
. On Unix, when theerrno
value isEINTR
, indicating an interrupted system call, this callsPyErr_CheckSignals()
, and if that set the error indicator, leaves it set to that. The function always returnsNULL
, so a wrapper function around a system call can writereturn 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 notNULL
, it is passed to the constructor of type as a third parameter. In the case ofOSError
exception, this is used to define thefilename
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 of0
, the error code returned by a call toGetLastError()
is used instead. It calls the Win32 functionFormatMessage()
to retrieve the Windows description of error code given by ierr orGetLastError()
, then it constructs aOSError
object with thewinerror
attribute set to the error code, thestrerror
attribute set to the corresponding error message (gotten fromFormatMessage()
), and then callsPyErr_SetObject(PyExc_OSError, object)
. This function always returnsNULL
.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 notNULL
, it is decoded from the filesystem encoding (os.fsdecode()
) and passed to the constructor ofOSError
as a third parameter to be used to define thefilename
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 notNULL
, it is passed to the constructor ofOSError
as a third parameter to be used to define thefilename
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 beNULL
, will be set as theImportError
’s respectivename
andpath
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 ofImportError
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 aSyntaxError
.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 callingPyErr_WarnEx()
, 2 is the function above that, and so forth.Warning categories must be subclasses of
PyExc_Warning
;PyExc_Warning
is a subclass ofPyExc_Exception
; the default warning category isPyExc_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_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 toNULL
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 usePyUnicode_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 usesPyUnicode_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 isResourceWarning
and it passes source towarnings.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 toPyErr_Restore()
). If not set, returnNULL
. You do not own a reference to the return value, so you do not need toPy_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.
Warning
This call steals a reference to exc, which must be a valid exception.
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 beNULL
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 aNULL
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 orNULL
. 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, passNULL
.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 beNULL
. Does not modify the exception info state. This function is kept for backwards compatibility. Prefer usingPyErr_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, passNULL
for all three arguments. This function is kept for backwards compatibility. Prefer usingPyErr_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
andtraceback
arguments are no longer used and can be NULL. The interpreter now derives them from the exception instance (thevalue
argument). The function still steals references of all three arguments.
Signal Handling¶
-
int PyErr_CheckSignals()¶
- Part of the Stable ABI.
This function interacts with Python’s signal handling.
If the function is called from the main thread and under the main Python interpreter, it checks whether a signal has been sent to the processes and if so, invokes the corresponding signal handler. If the
signal
module is supported, this can invoke a signal handler written in Python.The function attempts to handle all pending signals, and then returns
0
. However, if a Python signal handler raises an exception, the error indicator is set and the function returns-1
immediately (such that other pending signals may not have been handled yet: they will be on the nextPyErr_CheckSignals()
invocation).If the function is called from a non-main thread, or under a non-main Python interpreter, it does nothing and returns
0
.This function can be called by long-running C code that wants to be interruptible by user requests (such as by pressing Ctrl-C).
Note
The default Python signal handler for
SIGINT
raises theKeyboardInterrupt
exception.
-
void PyErr_SetInterrupt()¶
- Part of the Stable ABI.
Simulate the effect of a
SIGINT
signal arriving. This is equivalent toPyErr_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
orsignal.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 tosignal.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 normallyNULL
. This creates a class object derived fromException
(accessible in C asPyExc_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.
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 returnsNULL
.
-
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 returnsNULL
.
-
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 byraise ... 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 orNone
. This steals a reference to cause.The
__suppress_context__
attribute is implicitly set toTrue
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 theexcept*
clauses (so they have a different traceback from orig) and those that were reraised (and have the same traceback as orig). Return theExceptionGroup
that needs to be reraised in the end, orNone
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
. Return0
on success,-1
on failure.If the
UnicodeError.object
is an empty sequence, the resulting start is0
. Otherwise, it is clipped to[0, len(object) - 1]
.See also
-
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
. Return0
on success,-1
on failure.If the
UnicodeError.object
is an empty sequence, the resulting end is0
. 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
-
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.where should be a UTF-8 encoded string such as
" in instance check"
to be concatenated to theRecursionError
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.
-
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 ofPy_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{...}
andlist
objects return[...]
.The function will return a negative integer if the recursion limit is reached. In that case the
tp_repr
implementation should typically returnNULL
.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 ofPy_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
-
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
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:
Exception types¶
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Added in version 3.3: PyExc_BlockingIOError
, PyExc_BrokenPipeError
,
PyExc_ChildProcessError
, PyExc_ConnectionError
,
PyExc_ConnectionAbortedError
, PyExc_ConnectionRefusedError
,
PyExc_ConnectionResetError
, PyExc_FileExistsError
,
PyExc_FileNotFoundError
, PyExc_InterruptedError
,
PyExc_IsADirectoryError
, PyExc_NotADirectoryError
,
PyExc_PermissionError
, PyExc_ProcessLookupError
and PyExc_TimeoutError
were introduced following PEP 3151.
Added in version 3.5: PyExc_StopAsyncIteration
and PyExc_RecursionError
.
Added in version 3.6: PyExc_ModuleNotFoundError
.
Added in version 3.11: PyExc_BaseExceptionGroup
.
OSError aliases¶
The following are a compatibility aliases to PyExc_OSError
.
Changed in version 3.3: These aliases used to be separate exception types.
C name |
Python name |
Notes |
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Notes:
PyExc_WindowsError
is only defined on Windows; protect code that
uses this by testing that the preprocessor macro MS_WINDOWS
is defined.
Warning types¶
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Added in version 3.2: PyExc_ResourceWarning
.
Added in version 3.10: PyExc_EncodingWarning
.
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.


Floating-Point Objects

Floating-Point Objects¶
-
PyTypeObject PyFloat_Type¶
- Part of the Stable ABI.
This instance of
PyTypeObject
represents the Python floating-point type. This is the same object asfloat
in the Python layer.
-
int PyFloat_Check(PyObject *p)¶
Return true if its argument is a
PyFloatObject
or a subtype ofPyFloatObject
. This function always succeeds.
-
int PyFloat_CheckExact(PyObject *p)¶
Return true if its argument is a
PyFloatObject
, but not a subtype ofPyFloatObject
. This function always succeeds.
-
PyObject *PyFloat_FromString(PyObject *str)¶
- Return value: New reference. Part of the Stable ABI.
Create a
PyFloatObject
object based on the string value in str, orNULL
on failure.
-
PyObject *PyFloat_FromDouble(double v)¶
- Return value: New reference. Part of the Stable ABI.
Create a
PyFloatObject
object from v, orNULL
on failure.
-
double PyFloat_AsDouble(PyObject *pyfloat)¶
- Part of the Stable ABI.
Return a C double representation of the contents of pyfloat. If pyfloat is not a Python floating-point object but has a
__float__()
method, this method will first be called to convert pyfloat into a float. If__float__()
is not defined then it falls back to__index__()
. This method returns-1.0
upon failure, so one should callPyErr_Occurred()
to check for errors.Changed in version 3.8: Use
__index__()
if available.
-
double PyFloat_AS_DOUBLE(PyObject *pyfloat)¶
Return a C double representation of the contents of pyfloat, but without error checking.
-
PyObject *PyFloat_GetInfo(void)¶
- Return value: New reference. Part of the Stable ABI.
Return a structseq instance which contains information about the precision, minimum and maximum values of a float. It’s a thin wrapper around the header file
float.h
.
-
double PyFloat_GetMax()¶
- Part of the Stable ABI.
Return the maximum representable finite float DBL_MAX as C double.
-
double PyFloat_GetMin()¶
- Part of the Stable ABI.
Return the minimum normalized positive float DBL_MIN as C double.
-
Py_INFINITY¶
This macro expands to a constant expression of type double, that represents the positive infinity.
On most platforms, this is equivalent to the
INFINITY
macro from the C11 standard<math.h>
header.
-
Py_NAN¶
This macro expands to a constant expression of type double, that represents a quiet not-a-number (qNaN) value.
On most platforms, this is equivalent to the
NAN
macro from the C11 standard<math.h>
header.
-
Py_HUGE_VAL¶
Equivalent to
INFINITY
.Deprecated since version 3.14: The macro is soft deprecated.
-
Py_MATH_TAU¶
The definition (accurate for a double type) of the
math.tau
constant.Added in version 3.6.
-
Py_RETURN_NAN¶
Return
math.nan
from a function.On most platforms, this is equivalent to
return PyFloat_FromDouble(NAN)
.
-
Py_RETURN_INF(sign)¶
Return
math.inf
or-math.inf
from a function, depending on the sign of sign.On most platforms, this is equivalent to the following:
return PyFloat_FromDouble(copysign(INFINITY, sign));
-
Py_IS_FINITE(X)¶
Return
1
if the given floating-point number X is finite, that is, it is normal, subnormal or zero, but not infinite or NaN. Return0
otherwise.Deprecated since version 3.14: The macro is soft deprecated. Use
isfinite
instead.
-
Py_IS_INFINITY(X)¶
Return
1
if the given floating-point number X is positive or negative infinity. Return0
otherwise.Deprecated since version 3.14: The macro is soft deprecated. Use
isinf
instead.
-
Py_IS_NAN(X)¶
Return
1
if the given floating-point number X is a not-a-number (NaN) value. Return0
otherwise.Deprecated since version 3.14: The macro is soft deprecated. Use
isnan
instead.
Pack and Unpack functions¶
The pack and unpack functions provide an efficient platform-independent way to store floating-point values as byte strings. The Pack routines produce a bytes string from a C double, and the Unpack routines produce a C double from such a bytes string. The suffix (2, 4 or 8) specifies the number of bytes in the bytes string.
On platforms that appear to use IEEE 754 formats these functions work by copying bits. On other platforms, the 2-byte format is identical to the IEEE 754 binary16 half-precision format, the 4-byte format (32-bit) is identical to the IEEE 754 binary32 single precision format, and the 8-byte format to the IEEE 754 binary64 double precision format, although the packing of INFs and NaNs (if such things exist on the platform) isn’t handled correctly, and attempting to unpack a bytes string containing an IEEE INF or NaN will raise an exception.
Note that NaNs type may not be preserved on IEEE platforms (signaling NaN become quiet NaN), for example on x86 systems in 32-bit mode.
On non-IEEE platforms with more precision, or larger dynamic range, than IEEE 754 supports, not all values can be packed; on non-IEEE platforms with less precision, or smaller dynamic range, not all values can be unpacked. What happens in such cases is partly accidental (alas).
Added in version 3.11.
Pack functions¶
The pack routines write 2, 4 or 8 bytes, starting at p. le is an
int argument, non-zero if you want the bytes string in little-endian
format (exponent last, at p+1
, p+3
, or p+6
p+7
), zero if you
want big-endian format (exponent first, at p). The PY_BIG_ENDIAN
constant can be used to use the native endian: it is equal to 1
on big
endian processor, or 0
on little endian processor.
Return value: 0
if all is OK, -1
if error (and an exception is set,
most likely OverflowError
).
There are two problems on non-IEEE platforms:
What this does is undefined if x is a NaN or infinity.
-0.0
and+0.0
produce the same bytes string.
-
int PyFloat_Pack2(double x, char *p, int le)¶
Pack a C double as the IEEE 754 binary16 half-precision format.
-
int PyFloat_Pack4(double x, char *p, int le)¶
Pack a C double as the IEEE 754 binary32 single precision format.
-
int PyFloat_Pack8(double x, char *p, int le)¶
Pack a C double as the IEEE 754 binary64 double precision format.
Unpack functions¶
The unpack routines read 2, 4 or 8 bytes, starting at p. le is an
int argument, non-zero if the bytes string is in little-endian format
(exponent last, at p+1
, p+3
or p+6
and p+7
), zero if big-endian
(exponent first, at p). The PY_BIG_ENDIAN
constant can be used to
use the native endian: it is equal to 1
on big endian processor, or 0
on little endian processor.
Return value: The unpacked double. On error, this is -1.0
and
PyErr_Occurred()
is true (and an exception is set, most likely
OverflowError
).
Note that on a non-IEEE platform this will refuse to unpack a bytes string that represents a NaN or infinity.
-
double PyFloat_Unpack2(const char *p, int le)¶
Unpack the IEEE 754 binary16 half-precision format as a C double.
-
double PyFloat_Unpack4(const char *p, int le)¶
Unpack the IEEE 754 binary32 single precision format as a C double.
-
double PyFloat_Unpack8(const char *p, int le)¶
Unpack the IEEE 754 binary64 double precision format as a C double.


— Determine type of sound file

sndhdr
— Determine type of sound file¶
Deprecated since version 3.11, removed in version 3.13.
This module is no longer part of the Python standard library. It was removed in Python 3.13 after being deprecated in Python 3.11. The removal was decided in PEP 594.
Possible replacements are third-party modules from PyPI: filetype, puremagic, or python-magic. These are not supported or maintained by the Python core team.
The last version of Python that provided the sndhdr
module was
Python 3.12.