Python/import.c (part 3)

Source:

cpython 3.14 @ ab2d84fe1023/Python/import.c ↗

This annotation covers C extension caching, code module execution, and importlib.reload. See python_import_detail and python_import2_detail for the import lock, sys.modules, and _find_and_load.

Map

Lines	Symbol	Role
1-80	_PyImport_FixupExtensionObject	Cache a loaded C extension in _PyImport_Extensions
81-200	PyImport_ExecCodeModuleObject	Execute a code object in a module dict
201-350	PyImport_ReloadModule	importlib.reload(module)
351-500	_PyImport_IsInitialized	Check that sys.modules exists (interpreter is ready)
501-700	_PyImport_GetModuleAttr	module.attribute with import-safe error handling

Reading

_PyImport_FixupExtensionObject

// CPython: Python/import.c:88 _PyImport_FixupExtensionObject
int
_PyImport_FixupExtensionObject(PyObject *mod, PyObject *name,
                                PyObject *filename, PyObject *modules)
{
    /* After a C extension is loaded:
       1. Store mod in sys.modules[name]
       2. Cache in _PyImport_Extensions[filename + name] for sub-interpreter reuse */
    if (PyObject_SetItem(modules, name, mod) < 0) return -1;
    /* If the module def has a per-interpreter state, don't cache it */
    if (def->m_base.m_init != NULL) return 0;  /* multi-phase: skip cache */
    PyObject *key = PyTuple_Pack(2, filename, name);
    PyDict_SetItem(_PyImport_Extensions, key, mod);
    ...
}

C extension caching avoids re-calling PyInit_* for the same extension across importlib.import_module calls.

PyImport_ExecCodeModuleObject

// CPython: Python/import.c:160 PyImport_ExecCodeModuleObject
PyObject *
PyImport_ExecCodeModuleObject(PyObject *name, PyObject *co,
                               PyObject *pathname, PyObject *cpathname)
{
    /* Create or find module in sys.modules, then exec the code object in it */
    PyObject *mod = import_get_module(tstate, name);
    if (mod == NULL)
        mod = PyImport_AddModuleObject(name);
    PyObject *d = PyModule_GetDict(mod);
    PyDict_SetItemString(d, "__file__", pathname);
    /* Execute code object (the module body) */
    PyObject *v = PyEval_EvalCode(co, d, d);
    if (v == NULL) {
        /* On error: remove from sys.modules */
        PyDict_DelItem(tstate->interp->modules, name);
        return NULL;
    }
    Py_DECREF(v);
    return mod;
}

PyImport_ReloadModule

// CPython: Python/import.c:260 PyImport_ReloadModule
PyObject *
PyImport_ReloadModule(PyObject *m)
{
    /* importlib.reload(m): re-execute the module's code in its existing dict.
       sys.modules[name] is preserved so references remain valid. */
    PyObject *reloaded = PyObject_CallMethodObjArgs(
        interp->importlib, &_Py_ID(reload), m, NULL);
    return reloaded;
}

reload calls importlib.reload which re-runs _find_and_load but reuses the existing module object. New code replaces old bindings in module.__dict__.

gopy notes

_PyImport_FixupExtensionObject is vm.FixupExtension in vm/eval_import.go. PyImport_ExecCodeModuleObject is vm.ExecCodeModule. PyImport_ReloadModule calls vm.ImportlibReload. The extension cache is vm.extensionCache (a sync.Map).