Python/ceval.c (part 4)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers exception handling, with statement, and structural pattern matching opcodes. See python_ceval_detail (part 3) for iteration and container opcodes.

Map

Lines	Symbol	Role
1-200	PUSH_EXC_INFO, POP_EXCEPT	Push/pop the exception info block
201-400	RAISE_VARARGS, RERAISE	raise and reraise
401-600	CLEANUP_THROW, YIELD_VALUE	Generator send/throw/close
601-800	BEFORE_WITH, WITH_EXCEPT_START	with statement management
801-1000	COPY_FREE_VARS, MAKE_CELL	Closure cell setup
1001-1200	MATCH_CLASS, MATCH_MAPPING, MATCH_SEQUENCE, MATCH_KEYS	Structural pattern matching
1201-1400	COPY, SWAP	Stack manipulation
1401-5500	Specialized opcodes	_BINARY_OP_ADD_INT, _LOAD_ATTR_MODULE, etc.

Reading

RAISE_VARARGS

// CPython: Python/ceval.c:2940 RAISE_VARARGS
inst(RAISE_VARARGS, (args[oparg] -- )) {
    PyObject *cause = NULL, *exc = NULL;
    switch (oparg) {
    case 2:
        cause = args[1];
        /* fall through */
    case 1:
        exc = args[0];
        /* fall through */
    case 0:
        if (do_raise(tstate, exc, cause)) {
            ...
        }
    }
    ...
}

oparg=0: bare raise (reraise current exception). oparg=1: raise exc. oparg=2: raise exc from cause.

PUSH_EXC_INFO and POP_EXCEPT

PUSH_EXC_INFO saves the current exception onto the exception stack and sets the new exception as current. POP_EXCEPT restores the previous exception from the stack.

// CPython: Python/ceval.c:2885 PUSH_EXC_INFO
inst(PUSH_EXC_INFO, (new_exc -- prev_exc, new_exc)) {
    _PyErr_StackItem *exc_info = tstate->exc_info;
    prev_exc = exc_info->exc_value;
    exc_info->exc_value = Py_NewRef(new_exc);
}

BEFORE_WITH and WITH_EXCEPT_START

BEFORE_WITH calls __enter__ on the context manager and pushes the result. WITH_EXCEPT_START calls __exit__ with the exception info when the with body raises.

// CPython: Python/ceval.c:3380 BEFORE_WITH
inst(BEFORE_WITH, (mgr -- exit, res)) {
    PyObject *enter = _PyObject_LookupSpecial(mgr, &_Py_ID(__enter__));
    ...
    exit = _PyObject_LookupSpecial(mgr, &_Py_ID(__exit__));
    ...
    res = _PyObject_CallNoArgs(enter);
}

MATCH_CLASS

Pattern matching in Python 3.10+. MATCH_CLASS checks if TOS is an instance of the pattern class and extracts keyword attributes.

// CPython: Python/ceval.c:3580 MATCH_CLASS
inst(MATCH_CLASS, (subject, type, names -- attrs)) {
    assert(PyTuple_CheckExact(names));
    attrs = _PyMatchCase_IsInstance(tstate, subject, type, names, oparg);
    ...
}

gopy notes

Exception handling opcodes are in vm/eval_unwind.go. RAISE_VARARGS routes through errors.Raise. The exception stack (exc_info) maps to a field in vm.Frame. BEFORE_WITH / WITH_EXCEPT_START are in vm/eval_stmt.go. Match opcodes are partially implemented.