mirror of https://github.com/python/cpython
1084 lines
48 KiB
ReStructuredText
1084 lines
48 KiB
ReStructuredText
.. highlight:: c
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.. _exceptionhandling:
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******************
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Exception Handling
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******************
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The functions described in this chapter will let you handle and raise Python
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exceptions. It is important to understand some of the basics of Python
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exception handling. It works somewhat like the POSIX :c:data:`errno` variable:
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there is a global indicator (per thread) of the last error that occurred. Most
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C API functions don't clear this on success, but will set it to indicate the
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cause of the error on failure. Most C API functions also return an error
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indicator, usually ``NULL`` if they are supposed to return a pointer, or ``-1``
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if they return an integer (exception: the :c:func:`PyArg_\*` functions
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return ``1`` for success and ``0`` for failure).
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Concretely, the error indicator consists of three object pointers: the
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exception's type, the exception's value, and the traceback object. Any
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of those pointers can be ``NULL`` if non-set (although some combinations are
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forbidden, for example you can't have a non-``NULL`` traceback if the exception
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type is ``NULL``).
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When a function must fail because some function it called failed, it generally
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doesn't set the error indicator; the function it called already set it. It is
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responsible for either handling the error and clearing the exception or
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returning after cleaning up any resources it holds (such as object references or
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memory allocations); it should *not* continue normally if it is not prepared to
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handle the error. If returning due to an error, it is important to indicate to
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the caller that an error has been set. If the error is not handled or carefully
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propagated, additional calls into the Python/C API may not behave as intended
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and may fail in mysterious ways.
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.. note::
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The error indicator is **not** the result of :func:`sys.exc_info()`.
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The former corresponds to an exception that is not yet caught (and is
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therefore still propagating), while the latter returns an exception after
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it is caught (and has therefore stopped propagating).
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Printing and clearing
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=====================
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.. c:function:: void PyErr_Clear()
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Clear the error indicator. If the error indicator is not set, there is no
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effect.
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.. c:function:: void PyErr_PrintEx(int set_sys_last_vars)
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Print a standard traceback to ``sys.stderr`` and clear the error indicator.
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**Unless** the error is a ``SystemExit``, in that case no traceback is
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printed and the Python process will exit with the error code specified by
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the ``SystemExit`` instance.
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Call this function **only** when the error indicator is set. Otherwise it
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will cause a fatal error!
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If *set_sys_last_vars* is nonzero, the variables :data:`sys.last_type`,
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:data:`sys.last_value` and :data:`sys.last_traceback` will be set to the
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type, value and traceback of the printed exception, respectively.
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.. c:function:: void PyErr_Print()
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Alias for ``PyErr_PrintEx(1)``.
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.. c:function:: void PyErr_WriteUnraisable(PyObject *obj)
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Call :func:`sys.unraisablehook` using the current exception and *obj*
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argument.
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This utility function prints a warning message to ``sys.stderr`` when an
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exception has been set but it is impossible for the interpreter to actually
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raise the exception. It is used, for example, when an exception occurs in an
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:meth:`__del__` method.
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The function is called with a single argument *obj* that identifies the context
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in which the unraisable exception occurred. If possible,
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the repr of *obj* will be printed in the warning message.
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An exception must be set when calling this function.
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Raising exceptions
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==================
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These functions help you set the current thread's error indicator.
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For convenience, some of these functions will always return a
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``NULL`` pointer for use in a ``return`` statement.
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.. c:function:: void PyErr_SetString(PyObject *type, const char *message)
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This is the most common way to set the error indicator. The first argument
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specifies the exception type; it is normally one of the standard exceptions,
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e.g. :c:data:`PyExc_RuntimeError`. You need not increment its reference count.
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The second argument is an error message; it is decoded from ``'utf-8'``.
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.. c:function:: void PyErr_SetObject(PyObject *type, PyObject *value)
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This function is similar to :c:func:`PyErr_SetString` but lets you specify an
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arbitrary Python object for the "value" of the exception.
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.. c:function:: PyObject* PyErr_Format(PyObject *exception, const char *format, ...)
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This function sets the error indicator and returns ``NULL``. *exception*
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should be a Python exception class. The *format* and subsequent
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parameters help format the error message; they have the same meaning and
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values as in :c:func:`PyUnicode_FromFormat`. *format* is an ASCII-encoded
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string.
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.. c:function:: PyObject* PyErr_FormatV(PyObject *exception, const char *format, va_list vargs)
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Same as :c:func:`PyErr_Format`, but taking a :c:type:`va_list` argument rather
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than a variable number of arguments.
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.. versionadded:: 3.5
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.. c:function:: void PyErr_SetNone(PyObject *type)
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This is a shorthand for ``PyErr_SetObject(type, Py_None)``.
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.. c:function:: int PyErr_BadArgument()
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This is a shorthand for ``PyErr_SetString(PyExc_TypeError, message)``, where
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*message* indicates that a built-in operation was invoked with an illegal
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argument. It is mostly for internal use.
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.. c:function:: PyObject* PyErr_NoMemory()
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This is a shorthand for ``PyErr_SetNone(PyExc_MemoryError)``; it returns ``NULL``
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so an object allocation function can write ``return PyErr_NoMemory();`` when it
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runs out of memory.
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.. c:function:: PyObject* PyErr_SetFromErrno(PyObject *type)
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.. index:: single: strerror()
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This is a convenience function to raise an exception when a C library function
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has returned an error and set the C variable :c:data:`errno`. It constructs a
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tuple object whose first item is the integer :c:data:`errno` value and whose
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second item is the corresponding error message (gotten from :c:func:`strerror`),
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and then calls ``PyErr_SetObject(type, object)``. On Unix, when the
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:c:data:`errno` value is :const:`EINTR`, indicating an interrupted system call,
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this calls :c:func:`PyErr_CheckSignals`, and if that set the error indicator,
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leaves it set to that. The function always returns ``NULL``, so a wrapper
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function around a system call can write ``return PyErr_SetFromErrno(type);``
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when the system call returns an error.
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.. c:function:: PyObject* PyErr_SetFromErrnoWithFilenameObject(PyObject *type, PyObject *filenameObject)
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Similar to :c:func:`PyErr_SetFromErrno`, with the additional behavior that if
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*filenameObject* is not ``NULL``, it is passed to the constructor of *type* as
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a third parameter. In the case of :exc:`OSError` exception,
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this is used to define the :attr:`filename` attribute of the
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exception instance.
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.. c:function:: PyObject* PyErr_SetFromErrnoWithFilenameObjects(PyObject *type, PyObject *filenameObject, PyObject *filenameObject2)
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Similar to :c:func:`PyErr_SetFromErrnoWithFilenameObject`, but takes a second
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filename object, for raising errors when a function that takes two filenames
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fails.
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.. versionadded:: 3.4
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.. c:function:: PyObject* PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)
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Similar to :c:func:`PyErr_SetFromErrnoWithFilenameObject`, but the filename
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is given as a C string. *filename* is decoded from the :term:`filesystem
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encoding and error handler`.
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.. c:function:: PyObject* PyErr_SetFromWindowsErr(int ierr)
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This is a convenience function to raise :exc:`WindowsError`. If called with
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*ierr* of :c:data:`0`, the error code returned by a call to :c:func:`GetLastError`
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is used instead. It calls the Win32 function :c:func:`FormatMessage` to retrieve
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the Windows description of error code given by *ierr* or :c:func:`GetLastError`,
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then it constructs a tuple object whose first item is the *ierr* value and whose
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second item is the corresponding error message (gotten from
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:c:func:`FormatMessage`), and then calls ``PyErr_SetObject(PyExc_WindowsError,
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object)``. This function always returns ``NULL``.
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.. availability:: Windows.
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.. c:function:: PyObject* PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)
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Similar to :c:func:`PyErr_SetFromWindowsErr`, with an additional parameter
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specifying the exception type to be raised.
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.. availability:: Windows.
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.. c:function:: PyObject* PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)
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Similar to :c:func:`PyErr_SetFromWindowsErrWithFilenameObject`, but the
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filename is given as a C string. *filename* is decoded from the filesystem
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encoding (:func:`os.fsdecode`).
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.. availability:: Windows.
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.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObject(PyObject *type, int ierr, PyObject *filename)
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Similar to :c:func:`PyErr_SetFromWindowsErrWithFilenameObject`, with an
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additional parameter specifying the exception type to be raised.
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.. availability:: Windows.
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.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObjects(PyObject *type, int ierr, PyObject *filename, PyObject *filename2)
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Similar to :c:func:`PyErr_SetExcFromWindowsErrWithFilenameObject`,
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but accepts a second filename object.
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.. availability:: Windows.
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.. versionadded:: 3.4
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.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, const char *filename)
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Similar to :c:func:`PyErr_SetFromWindowsErrWithFilename`, with an additional
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parameter specifying the exception type to be raised.
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.. availability:: Windows.
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.. c:function:: PyObject* PyErr_SetImportError(PyObject *msg, PyObject *name, PyObject *path)
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This is a convenience function to raise :exc:`ImportError`. *msg* will be
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set as the exception's message string. *name* and *path*, both of which can
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be ``NULL``, will be set as the :exc:`ImportError`'s respective ``name``
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and ``path`` attributes.
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.. versionadded:: 3.3
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.. c:function:: PyObject* PyErr_SetImportErrorSubclass(PyObject *exception, PyObject *msg, PyObject *name, PyObject *path)
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Much like :c:func:`PyErr_SetImportError` but this function allows for
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specifying a subclass of :exc:`ImportError` to raise.
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.. versionadded:: 3.6
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.. c:function:: void PyErr_SyntaxLocationObject(PyObject *filename, int lineno, int col_offset)
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Set file, line, and offset information for the current exception. If the
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current exception is not a :exc:`SyntaxError`, then it sets additional
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attributes, which make the exception printing subsystem think the exception
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is a :exc:`SyntaxError`.
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.. versionadded:: 3.4
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.. c:function:: void PyErr_SyntaxLocationEx(const char *filename, int lineno, int col_offset)
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Like :c:func:`PyErr_SyntaxLocationObject`, but *filename* is a byte string
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decoded from the :term:`filesystem encoding and error handler`.
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.. versionadded:: 3.2
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.. c:function:: void PyErr_SyntaxLocation(const char *filename, int lineno)
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Like :c:func:`PyErr_SyntaxLocationEx`, but the col_offset parameter is
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omitted.
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.. c:function:: void PyErr_BadInternalCall()
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This is a shorthand for ``PyErr_SetString(PyExc_SystemError, message)``,
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where *message* indicates that an internal operation (e.g. a Python/C API
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function) was invoked with an illegal argument. It is mostly for internal
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use.
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Issuing warnings
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================
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Use these functions to issue warnings from C code. They mirror similar
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functions exported by the Python :mod:`warnings` module. They normally
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print a warning message to *sys.stderr*; however, it is
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also possible that the user has specified that warnings are to be turned into
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errors, and in that case they will raise an exception. It is also possible that
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the functions raise an exception because of a problem with the warning machinery.
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The return value is ``0`` if no exception is raised, or ``-1`` if an exception
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is raised. (It is not possible to determine whether a warning message is
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actually printed, nor what the reason is for the exception; this is
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intentional.) If an exception is raised, the caller should do its normal
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exception handling (for example, :c:func:`Py_DECREF` owned references and return
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an error value).
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.. c:function:: int PyErr_WarnEx(PyObject *category, const char *message, Py_ssize_t stack_level)
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Issue a warning message. The *category* argument is a warning category (see
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below) or ``NULL``; the *message* argument is a UTF-8 encoded string. *stack_level* is a
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positive number giving a number of stack frames; the warning will be issued from
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the currently executing line of code in that stack frame. A *stack_level* of 1
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is the function calling :c:func:`PyErr_WarnEx`, 2 is the function above that,
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and so forth.
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Warning categories must be subclasses of :c:data:`PyExc_Warning`;
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:c:data:`PyExc_Warning` is a subclass of :c:data:`PyExc_Exception`;
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the default warning category is :c:data:`PyExc_RuntimeWarning`. The standard
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Python warning categories are available as global variables whose names are
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enumerated at :ref:`standardwarningcategories`.
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For information about warning control, see the documentation for the
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:mod:`warnings` module and the :option:`-W` option in the command line
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documentation. There is no C API for warning control.
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.. c:function:: int PyErr_WarnExplicitObject(PyObject *category, PyObject *message, PyObject *filename, int lineno, PyObject *module, PyObject *registry)
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Issue a warning message with explicit control over all warning attributes. This
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is a straightforward wrapper around the Python function
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:func:`warnings.warn_explicit`, see there for more information. The *module*
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and *registry* arguments may be set to ``NULL`` to get the default effect
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described there.
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.. versionadded:: 3.4
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.. c:function:: int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)
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Similar to :c:func:`PyErr_WarnExplicitObject` except that *message* and
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*module* are UTF-8 encoded strings, and *filename* is decoded from the
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:term:`filesystem encoding and error handler`.
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.. c:function:: int PyErr_WarnFormat(PyObject *category, Py_ssize_t stack_level, const char *format, ...)
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Function similar to :c:func:`PyErr_WarnEx`, but use
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:c:func:`PyUnicode_FromFormat` to format the warning message. *format* is
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an ASCII-encoded string.
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.. versionadded:: 3.2
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.. c:function:: int PyErr_ResourceWarning(PyObject *source, Py_ssize_t stack_level, const char *format, ...)
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Function similar to :c:func:`PyErr_WarnFormat`, but *category* is
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:exc:`ResourceWarning` and it passes *source* to :func:`warnings.WarningMessage`.
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.. versionadded:: 3.6
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Querying the error indicator
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============================
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.. c:function:: PyObject* PyErr_Occurred()
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Test whether the error indicator is set. If set, return the exception *type*
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(the first argument to the last call to one of the :c:func:`PyErr_Set\*`
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functions or to :c:func:`PyErr_Restore`). If not set, return ``NULL``. You do not
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own a reference to the return value, so you do not need to :c:func:`Py_DECREF`
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it.
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The caller must hold the GIL.
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.. note::
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Do not compare the return value to a specific exception; use
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:c:func:`PyErr_ExceptionMatches` instead, shown below. (The comparison could
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easily fail since the exception may be an instance instead of a class, in the
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case of a class exception, or it may be a subclass of the expected exception.)
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.. c:function:: int PyErr_ExceptionMatches(PyObject *exc)
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Equivalent to ``PyErr_GivenExceptionMatches(PyErr_Occurred(), exc)``. This
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should only be called when an exception is actually set; a memory access
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violation will occur if no exception has been raised.
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.. c:function:: int PyErr_GivenExceptionMatches(PyObject *given, PyObject *exc)
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Return true if the *given* exception matches the exception type in *exc*. If
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*exc* is a class object, this also returns true when *given* is an instance
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of a subclass. If *exc* is a tuple, all exception types in the tuple (and
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recursively in subtuples) are searched for a match.
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.. c:function:: void PyErr_Fetch(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
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Retrieve the error indicator into three variables whose addresses are passed.
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If the error indicator is not set, set all three variables to ``NULL``. If it is
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set, it will be cleared and you own a reference to each object retrieved. The
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value and traceback object may be ``NULL`` even when the type object is not.
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.. note::
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This function is normally only used by code that needs to catch exceptions or
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by code that needs to save and restore the error indicator temporarily, e.g.::
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{
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PyObject *type, *value, *traceback;
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PyErr_Fetch(&type, &value, &traceback);
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/* ... code that might produce other errors ... */
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PyErr_Restore(type, value, traceback);
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}
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.. c:function:: void PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)
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Set the error indicator from the three objects. If the error indicator is
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already set, it is cleared first. If the objects are ``NULL``, the error
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indicator is cleared. Do not pass a ``NULL`` type and non-``NULL`` value or
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traceback. The exception type should be a class. Do not pass an invalid
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exception type or value. (Violating these rules will cause subtle problems
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later.) This call takes away a reference to each object: you must own a
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reference to each object before the call and after the call you no longer own
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these references. (If you don't understand this, don't use this function. I
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warned you.)
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.. note::
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This function is normally only used by code that needs to save and restore the
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error indicator temporarily. Use :c:func:`PyErr_Fetch` to save the current
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error indicator.
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.. c:function:: void PyErr_NormalizeException(PyObject**exc, PyObject**val, PyObject**tb)
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Under certain circumstances, the values returned by :c:func:`PyErr_Fetch` below
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can be "unnormalized", meaning that ``*exc`` is a class object but ``*val`` is
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not an instance of the same class. This function can be used to instantiate
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the class in that case. If the values are already normalized, nothing happens.
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The delayed normalization is implemented to improve performance.
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.. note::
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This function *does not* implicitly set the ``__traceback__``
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attribute on the exception value. If setting the traceback
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appropriately is desired, the following additional snippet is needed::
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if (tb != NULL) {
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PyException_SetTraceback(val, tb);
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}
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.. c:function:: void PyErr_GetExcInfo(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
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Retrieve the exception info, as known from ``sys.exc_info()``. This refers
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to an exception that was *already caught*, not to an exception that was
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freshly raised. Returns new references for the three objects, any of which
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may be ``NULL``. Does not modify the exception info state.
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.. note::
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This function is not normally used by code that wants to handle exceptions.
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Rather, it can be used when code needs to save and restore the exception
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state temporarily. Use :c:func:`PyErr_SetExcInfo` to restore or clear the
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exception state.
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.. versionadded:: 3.3
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|
|
.. 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.
|
|
|
|
.. 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.
|
|
|
|
|
|
Signal Handling
|
|
===============
|
|
|
|
|
|
.. c:function:: int PyErr_CheckSignals()
|
|
|
|
.. index::
|
|
module: signal
|
|
single: SIGINT
|
|
single: KeyboardInterrupt (built-in exception)
|
|
|
|
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 :mod:`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
|
|
next :c:func:`PyErr_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 :const:`SIGINT` raises the
|
|
:exc:`KeyboardInterrupt` exception.
|
|
|
|
|
|
.. c:function:: void PyErr_SetInterrupt()
|
|
|
|
.. index::
|
|
module: signal
|
|
single: SIGINT
|
|
single: KeyboardInterrupt (built-in exception)
|
|
|
|
Simulate the effect of a :const:`SIGINT` signal arriving.
|
|
This is equivalent to ``PyErr_SetInterruptEx(SIGINT)``.
|
|
|
|
.. note::
|
|
This function is async-signal-safe. It can be called without
|
|
the :term:`GIL` and from a C signal handler.
|
|
|
|
|
|
.. c:function:: int PyErr_SetInterruptEx(int signum)
|
|
|
|
.. index::
|
|
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
|
|
:data:`signal.SIG_DFL` or :data:`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
|
|
the :term:`GIL` 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.
|
|
|
|
|
|
Exception Classes
|
|
=================
|
|
|
|
.. 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:`__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
|
|
|
|
|
|
Exception Objects
|
|
=================
|
|
|
|
.. c:function:: PyObject* PyException_GetTraceback(PyObject *ex)
|
|
|
|
Return the traceback associated with the exception as a new reference, as
|
|
accessible from Python through :attr:`__traceback__`. 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 :attr:`__context__`. 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 :const:`None`,
|
|
set by ``raise ... from ...``) associated with the exception as a new
|
|
reference, as accessible from Python through :attr:`__cause__`.
|
|
|
|
|
|
.. 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 :const:`None`. This steals a reference to *cause*.
|
|
|
|
:attr:`__suppress_context__` is implicitly set to ``True`` by this function.
|
|
|
|
|
|
.. _unicodeexceptions:
|
|
|
|
Unicode Exception Objects
|
|
=========================
|
|
|
|
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.
|
|
|
|
.. 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.
|
|
|
|
.. 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.
|
|
|
|
.. 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.
|
|
|
|
.. 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:
|
|
|
|
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 :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.
|
|
|
|
If :const:`USE_STACKCHECK` is defined, this function checks if the OS
|
|
stack overflowed using :c:func:`PyOS_CheckStack`. In this is the case, it
|
|
sets a :exc:`MemoryError` and returns a nonzero value.
|
|
|
|
The function then checks if the recursion 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.
|
|
|
|
.. versionchanged:: 3.9
|
|
This function is now also available in the limited 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 limited 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.
|
|
|
|
|
|
.. _standardexceptions:
|
|
|
|
Standard Exceptions
|
|
===================
|
|
|
|
All standard Python exceptions are available as global variables whose names are
|
|
``PyExc_`` followed by the Python exception name. These have the type
|
|
:c:type:`PyObject*`; they are all class objects. For completeness, here are all
|
|
the variables:
|
|
|
|
.. index::
|
|
single: PyExc_BaseException
|
|
single: PyExc_Exception
|
|
single: PyExc_ArithmeticError
|
|
single: PyExc_AssertionError
|
|
single: PyExc_AttributeError
|
|
single: PyExc_BlockingIOError
|
|
single: PyExc_BrokenPipeError
|
|
single: PyExc_BufferError
|
|
single: PyExc_ChildProcessError
|
|
single: PyExc_ConnectionAbortedError
|
|
single: PyExc_ConnectionError
|
|
single: PyExc_ConnectionRefusedError
|
|
single: PyExc_ConnectionResetError
|
|
single: PyExc_EOFError
|
|
single: PyExc_FileExistsError
|
|
single: PyExc_FileNotFoundError
|
|
single: PyExc_FloatingPointError
|
|
single: PyExc_GeneratorExit
|
|
single: PyExc_ImportError
|
|
single: PyExc_IndentationError
|
|
single: PyExc_IndexError
|
|
single: PyExc_InterruptedError
|
|
single: PyExc_IsADirectoryError
|
|
single: PyExc_KeyError
|
|
single: PyExc_KeyboardInterrupt
|
|
single: PyExc_LookupError
|
|
single: PyExc_MemoryError
|
|
single: PyExc_ModuleNotFoundError
|
|
single: PyExc_NameError
|
|
single: PyExc_NotADirectoryError
|
|
single: PyExc_NotImplementedError
|
|
single: PyExc_OSError
|
|
single: PyExc_OverflowError
|
|
single: PyExc_PermissionError
|
|
single: PyExc_ProcessLookupError
|
|
single: PyExc_RecursionError
|
|
single: PyExc_ReferenceError
|
|
single: PyExc_RuntimeError
|
|
single: PyExc_StopAsyncIteration
|
|
single: PyExc_StopIteration
|
|
single: PyExc_SyntaxError
|
|
single: PyExc_SystemError
|
|
single: PyExc_SystemExit
|
|
single: PyExc_TabError
|
|
single: PyExc_TimeoutError
|
|
single: PyExc_TypeError
|
|
single: PyExc_UnboundLocalError
|
|
single: PyExc_UnicodeDecodeError
|
|
single: PyExc_UnicodeEncodeError
|
|
single: PyExc_UnicodeError
|
|
single: PyExc_UnicodeTranslateError
|
|
single: PyExc_ValueError
|
|
single: PyExc_ZeroDivisionError
|
|
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| C Name | Python Name | Notes |
|
|
+=========================================+=================================+==========+
|
|
| :c:data:`PyExc_BaseException` | :exc:`BaseException` | \(1) |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_Exception` | :exc:`Exception` | \(1) |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ArithmeticError` | :exc:`ArithmeticError` | \(1) |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_AssertionError` | :exc:`AssertionError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_AttributeError` | :exc:`AttributeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_BlockingIOError` | :exc:`BlockingIOError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_BrokenPipeError` | :exc:`BrokenPipeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_BufferError` | :exc:`BufferError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ChildProcessError` | :exc:`ChildProcessError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ConnectionAbortedError` | :exc:`ConnectionAbortedError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ConnectionError` | :exc:`ConnectionError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ConnectionRefusedError` | :exc:`ConnectionRefusedError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ConnectionResetError` | :exc:`ConnectionResetError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_EOFError` | :exc:`EOFError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_FileExistsError` | :exc:`FileExistsError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_FileNotFoundError` | :exc:`FileNotFoundError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_FloatingPointError` | :exc:`FloatingPointError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_GeneratorExit` | :exc:`GeneratorExit` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ImportError` | :exc:`ImportError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_IndentationError` | :exc:`IndentationError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_IndexError` | :exc:`IndexError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_InterruptedError` | :exc:`InterruptedError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_IsADirectoryError` | :exc:`IsADirectoryError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_KeyError` | :exc:`KeyError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_KeyboardInterrupt` | :exc:`KeyboardInterrupt` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_LookupError` | :exc:`LookupError` | \(1) |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_MemoryError` | :exc:`MemoryError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ModuleNotFoundError` | :exc:`ModuleNotFoundError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_NameError` | :exc:`NameError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_NotADirectoryError` | :exc:`NotADirectoryError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_NotImplementedError` | :exc:`NotImplementedError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_OSError` | :exc:`OSError` | \(1) |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_OverflowError` | :exc:`OverflowError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_PermissionError` | :exc:`PermissionError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ProcessLookupError` | :exc:`ProcessLookupError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_RecursionError` | :exc:`RecursionError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ReferenceError` | :exc:`ReferenceError` | \(2) |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_RuntimeError` | :exc:`RuntimeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_StopAsyncIteration` | :exc:`StopAsyncIteration` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_StopIteration` | :exc:`StopIteration` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_SyntaxError` | :exc:`SyntaxError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_SystemError` | :exc:`SystemError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_SystemExit` | :exc:`SystemExit` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_TabError` | :exc:`TabError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_TimeoutError` | :exc:`TimeoutError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_TypeError` | :exc:`TypeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UnboundLocalError` | :exc:`UnboundLocalError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UnicodeDecodeError` | :exc:`UnicodeDecodeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UnicodeEncodeError` | :exc:`UnicodeEncodeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UnicodeError` | :exc:`UnicodeError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UnicodeTranslateError` | :exc:`UnicodeTranslateError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ValueError` | :exc:`ValueError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ZeroDivisionError` | :exc:`ZeroDivisionError` | |
|
|
+-----------------------------------------+---------------------------------+----------+
|
|
|
|
.. 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`.
|
|
|
|
These are compatibility aliases to :c:data:`PyExc_OSError`:
|
|
|
|
.. index::
|
|
single: PyExc_EnvironmentError
|
|
single: PyExc_IOError
|
|
single: PyExc_WindowsError
|
|
|
|
+-------------------------------------+----------+
|
|
| C Name | Notes |
|
|
+=====================================+==========+
|
|
| :c:data:`PyExc_EnvironmentError` | |
|
|
+-------------------------------------+----------+
|
|
| :c:data:`PyExc_IOError` | |
|
|
+-------------------------------------+----------+
|
|
| :c:data:`PyExc_WindowsError` | \(3) |
|
|
+-------------------------------------+----------+
|
|
|
|
.. versionchanged:: 3.3
|
|
These aliases used to be separate exception types.
|
|
|
|
Notes:
|
|
|
|
(1)
|
|
This is a base class for other standard exceptions.
|
|
|
|
(2)
|
|
Only defined on Windows; protect code that uses this by testing that the
|
|
preprocessor macro ``MS_WINDOWS`` is defined.
|
|
|
|
.. _standardwarningcategories:
|
|
|
|
Standard Warning Categories
|
|
===========================
|
|
|
|
All standard Python warning categories are available as global variables whose
|
|
names are ``PyExc_`` followed by the Python exception name. These have the type
|
|
:c:type:`PyObject*`; they are all class objects. For completeness, here are all
|
|
the variables:
|
|
|
|
.. index::
|
|
single: PyExc_Warning
|
|
single: PyExc_BytesWarning
|
|
single: PyExc_DeprecationWarning
|
|
single: PyExc_FutureWarning
|
|
single: PyExc_ImportWarning
|
|
single: PyExc_PendingDeprecationWarning
|
|
single: PyExc_ResourceWarning
|
|
single: PyExc_RuntimeWarning
|
|
single: PyExc_SyntaxWarning
|
|
single: PyExc_UnicodeWarning
|
|
single: PyExc_UserWarning
|
|
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| C Name | Python Name | Notes |
|
|
+==========================================+=================================+==========+
|
|
| :c:data:`PyExc_Warning` | :exc:`Warning` | \(1) |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_BytesWarning` | :exc:`BytesWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_DeprecationWarning` | :exc:`DeprecationWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_FutureWarning` | :exc:`FutureWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ImportWarning` | :exc:`ImportWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_PendingDeprecationWarning`| :exc:`PendingDeprecationWarning`| |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_ResourceWarning` | :exc:`ResourceWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_RuntimeWarning` | :exc:`RuntimeWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_SyntaxWarning` | :exc:`SyntaxWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UnicodeWarning` | :exc:`UnicodeWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
| :c:data:`PyExc_UserWarning` | :exc:`UserWarning` | |
|
|
+------------------------------------------+---------------------------------+----------+
|
|
|
|
.. versionadded:: 3.2
|
|
:c:data:`PyExc_ResourceWarning`.
|
|
|
|
Notes:
|
|
|
|
(1)
|
|
This is a base class for other standard warning categories.
|