Lib/sys (Python/sysmodule.c)

Source:

cpython 3.14 @ ab2d84fe1023/Python/sysmodule.c ↗

The sys module exposes interpreter internals. It is implemented in C (Python/sysmodule.c) as a built-in module. Most attributes are simple wrappers around interpreter state fields.

Map

Lines	Symbol	Role
1-300	sys.argv, sys.path, sys.modules	Process and import state
301-600	sys.stdout, sys.stdin, sys.stderr	Standard streams
601-900	sys.exc_info, sys.last_exc	Current exception access
901-1200	sys._getframe, sys._getframemodulename	Frame introspection
1201-1500	sys.settrace, sys.setprofile	Trace/profile hooks
1501-1800	sys.intern, sys.getrefcount, sys.getsizeof	Object utilities
1801-2200	sys.version, sys.version_info, sys.platform	Version and platform
2201-3500	sys.exit, sys.getrecursionlimit, sys.setrecursionlimit	Runtime control

Reading

sys.exc_info

// CPython: Python/sysmodule.c:720 sys_exc_info_impl
static PyObject *
sys_exc_info_impl(PyObject *module)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return _PyErr_StackItem_To_Tuple(tstate->exc_info);
}

Returns (type, value, traceback) for the exception currently being handled. Returns (None, None, None) outside an except block.

sys._getframe

// CPython: Python/sysmodule.c:1045 sys__getframe_impl
static PyObject *
sys__getframe_impl(PyObject *module, int depth)
{
    PyFrameObject *f = PyEval_GetFrame();
    while (depth > 0 && f != NULL) {
        f = f->f_back;
        depth--;
    }
    if (f == NULL) {
        PyErr_SetString(PyExc_ValueError, "call stack is not deep enough");
        return NULL;
    }
    return (PyObject *)f;
}

sys._getframe(0) returns the current frame, sys._getframe(1) the caller's frame, etc.

sys.settrace

// CPython: Python/sysmodule.c:1180 sys_settrace_impl
static PyObject *
sys_settrace_impl(PyObject *module, PyObject *o)
{
    if (o == Py_None) {
        PyEval_SetTrace(NULL, NULL);
    } else {
        PyEval_SetTrace(trace_trampoline, o);
    }
    Py_RETURN_NONE;
}

PyEval_SetTrace sets c_tracefunc and c_traceobj on the thread state. The trace function is called for call, line, return, and exception events.

sys.intern

// CPython: Python/sysmodule.c:1540 sys_intern_impl
static PyObject *
sys_intern_impl(PyObject *module, PyObject *s)
{
    PyUnicode_InternInPlace(&s);
    return s;
}

sys.intern(s) adds s to the global string intern table, ensuring that all future occurrences of the same string use the same object. Useful for memory-intensive dict-key workloads.

gopy notes

sys is in module/sys/. sys.modules is the interpreter's module dict. sys.path controls import search. sys._getframe requires the frame chain to be traversable from vm.Interpreter. sys.settrace requires a trace hook interface on vm.Frame. sys.exc_info reads the exception stack from the current frame.