Python/ceval.c (part 58)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers exception raising and matching. See python_ceval57_detail for import opcodes.

Map

Lines	Symbol	Role
1-80	RAISE_VARARGS	raise, raise exc, raise exc from cause
81-160	RERAISE	raise (bare) in an except block
161-260	CHECK_EXC_MATCH	except ExcType: matching
261-360	CHECK_EG_MATCH	except* ExcType: for exception groups
361-500	Exception chaining logic	__cause__, __context__, __traceback__

Reading

RAISE_VARARGS

// CPython: Python/ceval.c:6020 RAISE_VARARGS
inst(RAISE_VARARGS, (args[oparg] -- )) {
    /* oparg: 0 = bare raise, 1 = raise exc, 2 = raise exc from cause */
    PyObject *cause = NULL, *exc = NULL;
    if (oparg == 2) {
        cause = args[1];
        exc   = args[0];
    } else if (oparg == 1) {
        exc = args[0];
    }
    int err = do_raise(tstate, exc, cause);
    if (err > 0) {
        assert(_PyErr_Occurred(tstate));
        Py_DECREF(exc);
        Py_XDECREF(cause);
        goto exception_unwind;
    }
    ...
}

do_raise handles the three forms: bare raise (re-raises the current exception), raise exc (raises exc with __context__ chaining), and raise exc from cause (sets __cause__ and __suppress_context__).

CHECK_EXC_MATCH

// CPython: Python/ceval.c:6080 CHECK_EXC_MATCH
inst(CHECK_EXC_MATCH, (left, right -- left, b)) {
    assert(PyExceptionInstance_Check(left));
    int res = PyErr_GivenExceptionMatches(left, right);
    b = res ? Py_True : Py_False;
    DISPATCH();
}

PyErr_GivenExceptionMatches handles tuples of exception types: except (ValueError, TypeError). It uses issubclass to check, so catching a base class catches all subclasses.

CHECK_EG_MATCH

// CPython: Python/ceval.c:6120 CHECK_EG_MATCH
inst(CHECK_EG_MATCH, (val, match_type -- rest, match)) {
    /* For 'except* ExcType:' — split the ExceptionGroup */
    PyObject *match, *rest;
    int res = _PyExc_Group_MatchAndExtract(val, match_type, &match, &rest);
    if (res < 0) ERROR_IF(true, error);
    /* match is the sub-group that matched, rest is the remainder */
    DISPATCH();
}

except* ValueError calls _PyExc_Group_MatchAndExtract which recursively walks the exception group, collecting matching exceptions into match and non-matching into rest.

gopy notes

RAISE_VARARGS is in vm/eval_unwind.go. It calls errors.Raise(exc, cause) which sets exc.__context__ and exc.__cause__. CHECK_EXC_MATCH calls objects.ExceptionMatches. CHECK_EG_MATCH calls objects.ExceptionGroupMatchAndExtract which uses objects.IsInstance recursively.