Python/errors.c (part 5)

Source:

cpython 3.14 @ ab2d84fe1023/Python/errors.c ↗

This annotation covers syntax error location, internal call errors, and miscellaneous helpers. See python_errors4_detail for PyErr_Format, chaining, and _PyErr_StackItem.

Map

Lines	Symbol	Role
1-80	PyErr_SyntaxLocationObject	Set filename/lineno/offset on a SyntaxError
81-180	PyErr_BadInternalCall	Raise SystemError for internal programming errors
181-280	_PyErr_TrySetFromCause	Set an error only if no error is already set
281-380	PyErr_WarnEx	Issue a warning via warnings.warn
381-500	_PyErr_ChainExceptions	Chain two exceptions manually

Reading

PyErr_SyntaxLocationObject

// CPython: Python/errors.c:1680 PyErr_SyntaxLocationObject
void
PyErr_SyntaxLocationObject(PyObject *filename, int lineno, int col_offset)
{
    /* Set the location fields on the current SyntaxError exception. */
    PyObject *exc = tstate->current_exception;
    if (exc == NULL || !PyErr_GivenExceptionMatches(exc, PyExc_SyntaxError))
        return;
    /* Set filename */
    if (filename != NULL)
        PyObject_SetAttr(exc, &_Py_ID(filename), filename);
    /* Set lineno */
    PyObject_SetAttr(exc, &_Py_ID(lineno), PyLong_FromLong(lineno));
    /* Set offset */
    if (col_offset != -1)
        PyObject_SetAttr(exc, &_Py_ID(offset), PyLong_FromLong(col_offset));
    /* Try to fill in the source text from the file */
    if (filename != NULL) {
        PyObject *source = _PyErr_GetSourceLine(filename, lineno);
        if (source) PyObject_SetAttr(exc, &_Py_ID(text), source);
    }
}

Called by the compiler and tokenizer to annotate SyntaxError with the exact source location. _PyErr_GetSourceLine opens the source file and reads line lineno for SyntaxError.text.

PyErr_BadInternalCall

// CPython: Python/errors.c:1780 PyErr_BadInternalCall
void
PyErr_BadInternalCall(void)
{
    /* Raise SystemError: bad argument to internal function */
    assert(0 && "bad argument to internal function");
    PyErr_SetString(PyExc_SystemError,
        "bad argument to internal function");
}

PyErr_BadInternalCall is called when a C extension passes NULL to a function that requires a valid Python object. The assert(0) fires in debug builds to catch the bug at the source.

PyErr_WarnEx

// CPython: Python/errors.c:1860 PyErr_WarnEx
int
PyErr_WarnEx(PyObject *category, const char *text, Py_ssize_t stack_level)
{
    /* Invoke warnings.warn(text, category, stacklevel=stack_level) */
    PyObject *warnings = PyImport_ImportModuleNoBlock("warnings");
    if (warnings == NULL) return -1;
    PyObject *warn = PyObject_GetAttr(warnings, &_Py_ID(warn));
    PyObject *res = PyObject_CallFunction(warn, "sOn",
                                          text, category, stack_level);
    Py_XDECREF(res);
    Py_DECREF(warn);
    Py_DECREF(warnings);
    return res == NULL ? -1 : 0;
}

PyErr_WarnEx(PyExc_DeprecationWarning, "use foo instead", 2) issues a DeprecationWarning pointing 2 frames up the call stack (the caller of the caller). Used by functools.wraps compatibility shims, deprecated API wrappers, etc.

_PyErr_ChainExceptions

// CPython: Python/errors.c:1940 _PyErr_ChainExceptions
void
_PyErr_ChainExceptions(PyObject *typ, PyObject *val, PyObject *tb)
{
    /* Set the current exception, chaining the existing one as __context__. */
    if (val == NULL) {
        Py_XDECREF(typ);
        Py_XDECREF(tb);
        return;
    }
    if (!PyExceptionInstance_Check(val)) {
        ...
    }
    PyObject *exc2 = tstate->current_exception;
    if (exc2 != NULL) {
        /* Chain: new exception's __context__ = old exception */
        Py_INCREF(exc2);
        PyException_SetContext(val, exc2);
    }
    _PyErr_Restore(tstate, typ, val, tb);
}

Used in C code that catches an exception (via PyErr_Fetch) and wants to raise a different exception while preserving the original as __context__.

gopy notes

PyErr_SyntaxLocationObject is errors.SyntaxLocationObject in vm/errors.go. PyErr_BadInternalCall is errors.BadInternalCall which calls panic in debug mode. PyErr_WarnEx is errors.WarnEx which dispatches to module/warnings. _PyErr_ChainExceptions is errors.ChainExceptions.