Python Programming

Error Handling 1

Extension modules indicate errors by returning NULL to the interpreter. Prior to returning NULL, an exception should be set using one of the following functions:

void PyErr_NoMemory()

Raises a MemoryError exception. void PyErr_SetFromErrno(PyObject *exc)

Raises an exception. exc is an exception object.The value of the exception is taken from the errno variable in the C library.

void PyErr_SetFromErrnoWithFilename(PyObject *exc, char *filename)

Like PyErr_SetFromErrno(), but includes the file name in the exception value as well.

void PyErr_SetObject(PyObject *exc, PyObject *val)

Raises an exception. exc is an exception object, and val is an object containing the value of the exception.

void PyErr_SetString(PyObject *exc, char *msg)

Raises an exception. exc is an exception object, and msg is a message describing what went wrong.

The exc argument in these functions	can be set to one of the following:
C Name	Python Exception
PyExc ArithmeticError	ArithmeticError
PyExc AssertionError	AssertionError
PyExc AttributeError	AttributeError
PyExc_EnvironmentError	EnvironmentError
PyExc_EOFError	EOFError
PyExc Exception	Exception
PyExc FloatingPointError	FloatingPointError
PyExc ImportError	ImportError
PyExc IndexError	IndexError
PyExc_IOError	IOError
PyExc KeyError	KeyError
PyExc KeyboardInterrupt	KeyboardInterrupt
PyExc LookupError	LookupError
PyExc_MemoryError	MemoryError
PyExc_NameError	NameError
PyExc_NotImplementedError	NotImplementedError

C Name		Python Exception
PyExc_	_OSError	OSError
PyExc_	OverflowError	OverflowError
PyExc_	ReferenceError	ReferenceError
PyExc_	RuntimeError	RuntimeError
PyExc_	StandardError	StandardError
PyExc_	StopIteration	StopIteration
PyExc_	SyntaxError	SyntaxError
PyExc_	SystemError	SystemError
PyExc_	SystemExit	SystemExit
PyExc_	TypeError	TypeError
PyExc_	UnicodeError	UnicodeError
PyExc_	UnicodeEncodeError	UnicodeEncodeError
PyExc_	UnicodeDecodeError	UnicodeDecodeError
PyExc_	UnicodeTranslateError	UnicodeTranslateError
PyExc_	ValueError	ValueError
PyExc_	WindowsError	WindowsError
PyExc_	ZeroDivisionError	ZeroDivisionError

The following functions are used to query or clear the exception status of the interpreter:

void PyErr_Clear()

Clears any previously raised exceptions. PyObject *PyErr_Occurred()

Checks to see whether or not an exception has been raised. If so, the current exception value is returned. Otherwise, NULL is returned.

int PyErr_ExceptionMatches(PyObject *exc)

Checks to see if the current exception matches the exception exc. Returns 1 if true, 0 otherwise. This function follows the same exception matching rules as in Python code. Therefore, exc could be a superclass of the current exception or a tuple of exception classes.

The following prototype shows how to implement a try-except block in C:

/* Carry out some operation involving Python objects */ if (PyErr_Occurred()) {

if (PyErr_ExceptionMatches(PyExc_ValueError)) { /* Take some kind of recovery action */

PyErr_Clear();

return NULL; /* Propagate the exception to the interpreter */

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