Python/import.c

/* Module definition and import implementation */

#include "Python.h"

#include "Python-ast.h"
#undef Yield   /* undefine macro conflicting with <winbase.h> */
#include "pycore_initconfig.h"
#include "pycore_pyerrors.h"
#include "pycore_pyhash.h"
#include "pycore_pylifecycle.h"
#include "pycore_pymem.h"         // _PyMem_SetDefaultAllocator()
#include "pycore_interp.h"        // _PyInterpreterState_ClearModules()
#include "pycore_pystate.h"       // _PyInterpreterState_GET()
#include "pycore_sysmodule.h"
#include "errcode.h"
#include "marshal.h"
#include "code.h"
#include "importdl.h"
#include "pydtrace.h"

#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef __cplusplus
extern "C" {
#endif

#define CACHEDIR "__pycache__"

/* Forward references */
static PyObject *import_add_module(PyThreadState *tstate, PyObject *name);

/* See _PyImport_FixupExtensionObject() below */
static PyObject *extensions = NULL;

/* This table is defined in config.c: */
extern struct _inittab _PyImport_Inittab[];

struct _inittab *PyImport_Inittab = _PyImport_Inittab;
static struct _inittab *inittab_copy = NULL;

_Py_IDENTIFIER(__path__);
_Py_IDENTIFIER(__spec__);

/*[clinic input]
module _imp
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=9c332475d8686284]*/

#include "clinic/import.c.h"

/* Initialize things */

PyStatus
_PyImportHooks_Init(PyThreadState *tstate)
{
    PyObject *v, *path_hooks = NULL;
    int err = 0;

    /* adding sys.path_hooks and sys.path_importer_cache */
    v = PyList_New(0);
    if (v == NULL)
        goto error;
    err = PySys_SetObject("meta_path", v);
    Py_DECREF(v);
    if (err)
        goto error;
    v = PyDict_New();
    if (v == NULL)
        goto error;
    err = PySys_SetObject("path_importer_cache", v);
    Py_DECREF(v);
    if (err)
        goto error;
    path_hooks = PyList_New(0);
    if (path_hooks == NULL)
        goto error;
    err = PySys_SetObject("path_hooks", path_hooks);
    if (err) {
        goto error;
    }
    Py_DECREF(path_hooks);
    return _PyStatus_OK();

  error:
    _PyErr_Print(tstate);
    return _PyStatus_ERR("initializing sys.meta_path, sys.path_hooks, "
                        "or path_importer_cache failed");
}

PyStatus
_PyImportZip_Init(PyThreadState *tstate)
{
    PyObject *path_hooks, *zipimport;
    int err = 0;

    path_hooks = PySys_GetObject("path_hooks");
    if (path_hooks == NULL) {
        _PyErr_SetString(tstate, PyExc_RuntimeError,
                         "unable to get sys.path_hooks");
        goto error;
    }

    int verbose = _PyInterpreterState_GetConfig(tstate->interp)->verbose;
    if (verbose) {
        PySys_WriteStderr("# installing zipimport hook\n");
    }

    zipimport = PyImport_ImportModule("zipimport");
    if (zipimport == NULL) {
        _PyErr_Clear(tstate); /* No zip import module -- okay */
        if (verbose) {
            PySys_WriteStderr("# can't import zipimport\n");
        }
    }
    else {
        _Py_IDENTIFIER(zipimporter);
        PyObject *zipimporter = _PyObject_GetAttrId(zipimport,
                                                    &PyId_zipimporter);
        Py_DECREF(zipimport);
        if (zipimporter == NULL) {
            _PyErr_Clear(tstate); /* No zipimporter object -- okay */
            if (verbose) {
                PySys_WriteStderr("# can't import zipimport.zipimporter\n");
            }
        }
        else {
            /* sys.path_hooks.insert(0, zipimporter) */
            err = PyList_Insert(path_hooks, 0, zipimporter);
            Py_DECREF(zipimporter);
            if (err < 0) {
                goto error;
            }
            if (verbose) {
                PySys_WriteStderr("# installed zipimport hook\n");
            }
        }
    }

    return _PyStatus_OK();

  error:
    PyErr_Print();
    return _PyStatus_ERR("initializing zipimport failed");
}

/* Locking primitives to prevent parallel imports of the same module
   in different threads to return with a partially loaded module.
   These calls are serialized by the global interpreter lock. */

static PyThread_type_lock import_lock = 0;
static unsigned long import_lock_thread = PYTHREAD_INVALID_THREAD_ID;
static int import_lock_level = 0;

void
_PyImport_AcquireLock(void)
{
    unsigned long me = PyThread_get_thread_ident();
    if (me == PYTHREAD_INVALID_THREAD_ID)
        return; /* Too bad */
    if (import_lock == NULL) {
        import_lock = PyThread_allocate_lock();
        if (import_lock == NULL)
            return;  /* Nothing much we can do. */
    }
    if (import_lock_thread == me) {
        import_lock_level++;
        return;
    }
    if (import_lock_thread != PYTHREAD_INVALID_THREAD_ID ||
        !PyThread_acquire_lock(import_lock, 0))
    {
        PyThreadState *tstate = PyEval_SaveThread();
        PyThread_acquire_lock(import_lock, 1);
        PyEval_RestoreThread(tstate);
    }
    assert(import_lock_level == 0);
    import_lock_thread = me;
    import_lock_level = 1;
}

int
_PyImport_ReleaseLock(void)
{
    unsigned long me = PyThread_get_thread_ident();
    if (me == PYTHREAD_INVALID_THREAD_ID || import_lock == NULL)
        return 0; /* Too bad */
    if (import_lock_thread != me)
        return -1;
    import_lock_level--;
    assert(import_lock_level >= 0);
    if (import_lock_level == 0) {
        import_lock_thread = PYTHREAD_INVALID_THREAD_ID;
        PyThread_release_lock(import_lock);
    }
    return 1;
}

#ifdef HAVE_FORK
/* This function is called from PyOS_AfterFork_Child to ensure that newly
   created child processes do not share locks with the parent.
   We now acquire the import lock around fork() calls but on some platforms
   (Solaris 9 and earlier? see isue7242) that still left us with problems. */

void
_PyImport_ReInitLock(void)
{
    if (import_lock != NULL) {
        if (_PyThread_at_fork_reinit(&import_lock) < 0) {
            _Py_FatalErrorFunc(__func__, "failed to create a new lock");
        }
    }
    if (import_lock_level > 1) {
        /* Forked as a side effect of import */
        unsigned long me = PyThread_get_thread_ident();
        /* The following could fail if the lock is already held, but forking as
           a side-effect of an import is a) rare, b) nuts, and c) difficult to
           do thanks to the lock only being held when doing individual module
           locks per import. */
        PyThread_acquire_lock(import_lock, NOWAIT_LOCK);
        import_lock_thread = me;
        import_lock_level--;
    } else {
        import_lock_thread = PYTHREAD_INVALID_THREAD_ID;
        import_lock_level = 0;
    }
}
#endif

/*[clinic input]
_imp.lock_held

Return True if the import lock is currently held, else False.

On platforms without threads, return False.
[clinic start generated code]*/

static PyObject *
_imp_lock_held_impl(PyObject *module)
/*[clinic end generated code: output=8b89384b5e1963fc input=9b088f9b217d9bdf]*/
{
    return PyBool_FromLong(import_lock_thread != PYTHREAD_INVALID_THREAD_ID);
}

/*[clinic input]
_imp.acquire_lock

Acquires the interpreter's import lock for the current thread.

This lock should be used by import hooks to ensure thread-safety when importing
modules. On platforms without threads, this function does nothing.
[clinic start generated code]*/

static PyObject *
_imp_acquire_lock_impl(PyObject *module)
/*[clinic end generated code: output=1aff58cb0ee1b026 input=4a2d4381866d5fdc]*/
{
    _PyImport_AcquireLock();
    Py_RETURN_NONE;
}

/*[clinic input]
_imp.release_lock

Release the interpreter's import lock.

On platforms without threads, this function does nothing.
[clinic start generated code]*/

static PyObject *
_imp_release_lock_impl(PyObject *module)
/*[clinic end generated code: output=7faab6d0be178b0a input=934fb11516dd778b]*/
{
    if (_PyImport_ReleaseLock() < 0) {
        PyErr_SetString(PyExc_RuntimeError,
                        "not holding the import lock");
        return NULL;
    }
    Py_RETURN_NONE;
}

void
_PyImport_Fini(void)
{
    Py_CLEAR(extensions);
    if (import_lock != NULL) {
        PyThread_free_lock(import_lock);
        import_lock = NULL;
    }
}

void
_PyImport_Fini2(void)
{
    /* Use the same memory allocator than PyImport_ExtendInittab(). */
    PyMemAllocatorEx old_alloc;
    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);

    /* Free memory allocated by PyImport_ExtendInittab() */
    PyMem_RawFree(inittab_copy);
    inittab_copy = NULL;

    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
}

/* Helper for sys */

PyObject *
PyImport_GetModuleDict(void)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    if (interp->modules == NULL) {
        Py_FatalError("interpreter has no modules dictionary");
    }
    return interp->modules;
}

/* In some corner cases it is important to be sure that the import
   machinery has been initialized (or not cleaned up yet).  For
   example, see issue #4236 and PyModule_Create2(). */

int
_PyImport_IsInitialized(PyInterpreterState *interp)
{
    if (interp->modules == NULL)
        return 0;
    return 1;
}

PyObject *
_PyImport_GetModuleId(struct _Py_Identifier *nameid)
{
    PyObject *name = _PyUnicode_FromId(nameid); /* borrowed */
    if (name == NULL) {
        return NULL;
    }
    return PyImport_GetModule(name);
}

int
_PyImport_SetModule(PyObject *name, PyObject *m)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *modules = tstate->interp->modules;
    return PyObject_SetItem(modules, name, m);
}

int
_PyImport_SetModuleString(const char *name, PyObject *m)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *modules = tstate->interp->modules;
    return PyMapping_SetItemString(modules, name, m);
}

static PyObject *
import_get_module(PyThreadState *tstate, PyObject *name)
{
    PyObject *modules = tstate->interp->modules;
    if (modules == NULL) {
        _PyErr_SetString(tstate, PyExc_RuntimeError,
                         "unable to get sys.modules");
        return NULL;
    }

    PyObject *m;
    Py_INCREF(modules);
    if (PyDict_CheckExact(modules)) {
        m = PyDict_GetItemWithError(modules, name);  /* borrowed */
        Py_XINCREF(m);
    }
    else {
        m = PyObject_GetItem(modules, name);
        if (m == NULL && _PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
            _PyErr_Clear(tstate);
        }
    }
    Py_DECREF(modules);
    return m;
}


static int
import_ensure_initialized(PyThreadState *tstate, PyObject *mod, PyObject *name)
{
    PyInterpreterState *interp = tstate->interp;
    PyObject *spec;

    _Py_IDENTIFIER(_lock_unlock_module);

    /* Optimization: only call _bootstrap._lock_unlock_module() if
       __spec__._initializing is true.
       NOTE: because of this, initializing must be set *before*
       stuffing the new module in sys.modules.
    */
    spec = _PyObject_GetAttrId(mod, &PyId___spec__);
    int busy = _PyModuleSpec_IsInitializing(spec);
    Py_XDECREF(spec);
    if (busy) {
        /* Wait until module is done importing. */
        PyObject *value = _PyObject_CallMethodIdOneArg(
            interp->importlib, &PyId__lock_unlock_module, name);
        if (value == NULL) {
            return -1;
        }
        Py_DECREF(value);
    }
    return 0;
}


/* List of names to clear in sys */
static const char * const sys_deletes[] = {
    "path", "argv", "ps1", "ps2",
    "last_type", "last_value", "last_traceback",
    "path_hooks", "path_importer_cache", "meta_path",
    "__interactivehook__",
    NULL
};

static const char * const sys_files[] = {
    "stdin", "__stdin__",
    "stdout", "__stdout__",
    "stderr", "__stderr__",
    NULL
};

/* Un-initialize things, as good as we can */

void
_PyImport_Cleanup(PyThreadState *tstate)
{
    PyInterpreterState *interp = tstate->interp;
    PyObject *modules = interp->modules;
    if (modules == NULL) {
        /* Already done */
        return;
    }

    /* Delete some special variables first.  These are common
       places where user values hide and people complain when their
       destructors fail.  Since the modules containing them are
       deleted *last* of all, they would come too late in the normal
       destruction order.  Sigh. */

    /* XXX Perhaps these precautions are obsolete. Who knows? */

    int verbose = _PyInterpreterState_GetConfig(interp)->verbose;
    if (verbose) {
        PySys_WriteStderr("# clear builtins._\n");
    }
    if (PyDict_SetItemString(interp->builtins, "_", Py_None) < 0) {
        PyErr_WriteUnraisable(NULL);
    }

    const char * const *p;
    for (p = sys_deletes; *p != NULL; p++) {
        if (verbose) {
            PySys_WriteStderr("# clear sys.%s\n", *p);
        }
        if (PyDict_SetItemString(interp->sysdict, *p, Py_None) < 0) {
            PyErr_WriteUnraisable(NULL);
        }
    }
    for (p = sys_files; *p != NULL; p+=2) {
        if (verbose) {
            PySys_WriteStderr("# restore sys.%s\n", *p);
        }
        PyObject *value = _PyDict_GetItemStringWithError(interp->sysdict,
                                                         *(p+1));
        if (value == NULL) {
            if (_PyErr_Occurred(tstate)) {
                PyErr_WriteUnraisable(NULL);
            }
            value = Py_None;
        }
        if (PyDict_SetItemString(interp->sysdict, *p, value) < 0) {
            PyErr_WriteUnraisable(NULL);
        }
    }

    /* We prepare a list which will receive (name, weakref) tuples of
       modules when they are removed from sys.modules.  The name is used
       for diagnosis messages (in verbose mode), while the weakref helps
       detect those modules which have been held alive. */
    PyObject *weaklist = PyList_New(0);
    if (weaklist == NULL) {
        PyErr_WriteUnraisable(NULL);
    }

#define STORE_MODULE_WEAKREF(name, mod) \
    if (weaklist != NULL) { \
        PyObject *wr = PyWeakref_NewRef(mod, NULL); \
        if (wr) { \
            PyObject *tup = PyTuple_Pack(2, name, wr); \
            if (!tup || PyList_Append(weaklist, tup) < 0) { \
                PyErr_WriteUnraisable(NULL); \
            } \
            Py_XDECREF(tup); \
            Py_DECREF(wr); \
        } \
        else { \
            PyErr_WriteUnraisable(NULL); \
        } \
    }
#define CLEAR_MODULE(name, mod) \
    if (PyModule_Check(mod)) { \
        if (verbose && PyUnicode_Check(name)) { \
            PySys_FormatStderr("# cleanup[2] removing %U\n", name); \
        } \
        STORE_MODULE_WEAKREF(name, mod); \
        if (PyObject_SetItem(modules, name, Py_None) < 0) { \
            PyErr_WriteUnraisable(NULL); \
        } \
    }

    /* Remove all modules from sys.modules, hoping that garbage collection
       can reclaim most of them. */
    if (PyDict_CheckExact(modules)) {
        Py_ssize_t pos = 0;
        PyObject *key, *value;
        while (PyDict_Next(modules, &pos, &key, &value)) {
            CLEAR_MODULE(key, value);
        }
    }
    else {
        PyObject *iterator = PyObject_GetIter(modules);
        if (iterator == NULL) {
            PyErr_WriteUnraisable(NULL);
        }
        else {
            PyObject *key;
            while ((key = PyIter_Next(iterator))) {
                PyObject *value = PyObject_GetItem(modules, key);
                if (value == NULL) {
                    PyErr_WriteUnraisable(NULL);
                    continue;
                }
                CLEAR_MODULE(key, value);
                Py_DECREF(value);
                Py_DECREF(key);
            }
            if (PyErr_Occurred()) {
                PyErr_WriteUnraisable(NULL);
            }
            Py_DECREF(iterator);
        }
    }

    /* Clear the modules dict. */
    if (PyDict_CheckExact(modules)) {
        PyDict_Clear(modules);
    }
    else {
        _Py_IDENTIFIER(clear);
        if (_PyObject_CallMethodIdNoArgs(modules, &PyId_clear) == NULL) {
            PyErr_WriteUnraisable(NULL);
        }
    }
    /* Restore the original builtins dict, to ensure that any
       user data gets cleared. */
    PyObject *dict = PyDict_Copy(interp->builtins);
    if (dict == NULL) {
        PyErr_WriteUnraisable(NULL);
    }
    PyDict_Clear(interp->builtins);
    if (PyDict_Update(interp->builtins, interp->builtins_copy)) {
        _PyErr_Clear(tstate);
    }
    Py_XDECREF(dict);
    /* Collect references */
    _PyGC_CollectNoFail();
    /* Dump GC stats before it's too late, since it uses the warnings
       machinery. */
    _PyGC_DumpShutdownStats(tstate);

    /* Now, if there are any modules left alive, clear their globals to
       minimize potential leaks.  All C extension modules actually end
       up here, since they are kept alive in the interpreter state.

       The special treatment of "builtins" here is because even
       when it's not referenced as a module, its dictionary is
       referenced by almost every module's __builtins__.  Since
       deleting a module clears its dictionary (even if there are
       references left to it), we need to delete the "builtins"
       module last.  Likewise, we don't delete sys until the very
       end because it is implicitly referenced (e.g. by print). */
    if (weaklist != NULL) {
        Py_ssize_t i;
        /* Since dict is ordered in CPython 3.6+, modules are saved in
           importing order.  First clear modules imported later. */
        for (i = PyList_GET_SIZE(weaklist) - 1; i >= 0; i--) {
            PyObject *tup = PyList_GET_ITEM(weaklist, i);
            PyObject *name = PyTuple_GET_ITEM(tup, 0);
            PyObject *mod = PyWeakref_GET_OBJECT(PyTuple_GET_ITEM(tup, 1));
            if (mod == Py_None)
                continue;
            assert(PyModule_Check(mod));
            dict = PyModule_GetDict(mod);
            if (dict == interp->builtins || dict == interp->sysdict)
                continue;
            Py_INCREF(mod);
            if (verbose && PyUnicode_Check(name)) {
                PySys_FormatStderr("# cleanup[3] wiping %U\n", name);
            }
            _PyModule_Clear(mod);
            Py_DECREF(mod);
        }
        Py_DECREF(weaklist);
    }

    /* Next, delete sys and builtins (in that order) */
    if (verbose) {
        PySys_FormatStderr("# cleanup[3] wiping sys\n");
    }
    _PyModule_ClearDict(interp->sysdict);
    if (verbose) {
        PySys_FormatStderr("# cleanup[3] wiping builtins\n");
    }
    _PyModule_ClearDict(interp->builtins);

    /* Clear module dict copies stored in the interpreter state */
    _PyInterpreterState_ClearModules(interp);

    /* Clear and delete the modules directory.  Actual modules will
       still be there only if imported during the execution of some
       destructor. */
    interp->modules = NULL;
    Py_DECREF(modules);

    /* Once more */
    _PyGC_CollectNoFail();

#undef CLEAR_MODULE
#undef STORE_MODULE_WEAKREF
}


/* Helper for pythonrun.c -- return magic number and tag. */

long
PyImport_GetMagicNumber(void)
{
    long res;
    PyInterpreterState *interp = _PyInterpreterState_GET();
    PyObject *external, *pyc_magic;

    external = PyObject_GetAttrString(interp->importlib, "_bootstrap_external");
    if (external == NULL)
        return -1;
    pyc_magic = PyObject_GetAttrString(external, "_RAW_MAGIC_NUMBER");
    Py_DECREF(external);
    if (pyc_magic == NULL)
        return -1;
    res = PyLong_AsLong(pyc_magic);
    Py_DECREF(pyc_magic);
    return res;
}


extern const char * _PySys_ImplCacheTag;

const char *
PyImport_GetMagicTag(void)
{
    return _PySys_ImplCacheTag;
}


/* Magic for extension modules (built-in as well as dynamically
   loaded).  To prevent initializing an extension module more than
   once, we keep a static dictionary 'extensions' keyed by the tuple
   (module name, module name)  (for built-in modules) or by
   (filename, module name) (for dynamically loaded modules), containing these
   modules.  A copy of the module's dictionary is stored by calling
   _PyImport_FixupExtensionObject() immediately after the module initialization
   function succeeds.  A copy can be retrieved from there by calling
   _PyImport_FindExtensionObject().

   Modules which do support multiple initialization set their m_size
   field to a non-negative number (indicating the size of the
   module-specific state). They are still recorded in the extensions
   dictionary, to avoid loading shared libraries twice.
*/

int
_PyImport_FixupExtensionObject(PyObject *mod, PyObject *name,
                               PyObject *filename, PyObject *modules)
{
    if (mod == NULL || !PyModule_Check(mod)) {
        PyErr_BadInternalCall();
        return -1;
    }

    struct PyModuleDef *def = PyModule_GetDef(mod);
    if (!def) {
        PyErr_BadInternalCall();
        return -1;
    }

    PyThreadState *tstate = _PyThreadState_GET();
    if (PyObject_SetItem(modules, name, mod) < 0) {
        return -1;
    }
    if (_PyState_AddModule(tstate, mod, def) < 0) {
        PyMapping_DelItem(modules, name);
        return -1;
    }

    if (_Py_IsMainInterpreter(tstate)) {
        if (def->m_size == -1) {
            if (def->m_base.m_copy) {
                /* Somebody already imported the module,
                   likely under a different name.
                   XXX this should really not happen. */
                Py_CLEAR(def->m_base.m_copy);
            }
            PyObject *dict = PyModule_GetDict(mod);
            if (dict == NULL) {
                return -1;
            }
            def->m_base.m_copy = PyDict_Copy(dict);
            if (def->m_base.m_copy == NULL) {
                return -1;
            }
        }

        if (extensions == NULL) {
            extensions = PyDict_New();
            if (extensions == NULL) {
                return -1;
            }
        }

        PyObject *key = PyTuple_Pack(2, filename, name);
        if (key == NULL) {
            return -1;
        }
        int res = PyDict_SetItem(extensions, key, (PyObject *)def);
        Py_DECREF(key);
        if (res < 0) {
            return -1;
        }
    }

    return 0;
}

int
_PyImport_FixupBuiltin(PyObject *mod, const char *name, PyObject *modules)
{
    int res;
    PyObject *nameobj;
    nameobj = PyUnicode_InternFromString(name);
    if (nameobj == NULL)
        return -1;
    res = _PyImport_FixupExtensionObject(mod, nameobj, nameobj, modules);
    Py_DECREF(nameobj);
    return res;
}

static PyObject *
import_find_extension(PyThreadState *tstate, PyObject *name,
                      PyObject *filename)
{
    if (extensions == NULL) {
        return NULL;
    }

    PyObject *key = PyTuple_Pack(2, filename, name);
    if (key == NULL) {
        return NULL;
    }
    PyModuleDef* def = (PyModuleDef *)PyDict_GetItemWithError(extensions, key);
    Py_DECREF(key);
    if (def == NULL) {
        return NULL;
    }

    PyObject *mod, *mdict;
    PyObject *modules = tstate->interp->modules;

    if (def->m_size == -1) {
        /* Module does not support repeated initialization */
        if (def->m_base.m_copy == NULL)
            return NULL;
        mod = import_add_module(tstate, name);
        if (mod == NULL)
            return NULL;
        mdict = PyModule_GetDict(mod);
        if (mdict == NULL)
            return NULL;
        if (PyDict_Update(mdict, def->m_base.m_copy))
            return NULL;
    }
    else {
        if (def->m_base.m_init == NULL)
            return NULL;
        mod = def->m_base.m_init();
        if (mod == NULL)
            return NULL;
        if (PyObject_SetItem(modules, name, mod) == -1) {
            Py_DECREF(mod);
            return NULL;
        }
        Py_DECREF(mod);
    }
    if (_PyState_AddModule(tstate, mod, def) < 0) {
        PyMapping_DelItem(modules, name);
        return NULL;
    }

    int verbose = _PyInterpreterState_GetConfig(tstate->interp)->verbose;
    if (verbose) {
        PySys_FormatStderr("import %U # previously loaded (%R)\n",
                           name, filename);
    }
    return mod;
}

PyObject *
_PyImport_FindExtensionObject(PyObject *name, PyObject *filename)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return import_find_extension(tstate, name, filename);
}


PyObject *
_PyImport_FindBuiltin(PyThreadState *tstate, const char *name)
{
    PyObject *res, *nameobj;
    nameobj = PyUnicode_InternFromString(name);
    if (nameobj == NULL)
        return NULL;
    res = import_find_extension(tstate, nameobj, nameobj);
    Py_DECREF(nameobj);
    return res;
}

/* Get the module object corresponding to a module name.
   First check the modules dictionary if there's one there,
   if not, create a new one and insert it in the modules dictionary.
   Because the former action is most common, THIS DOES NOT RETURN A
   'NEW' REFERENCE! */

static PyObject *
import_add_module(PyThreadState *tstate, PyObject *name)
{
    PyObject *modules = tstate->interp->modules;
    if (modules == NULL) {
        _PyErr_SetString(tstate, PyExc_RuntimeError,
                         "no import module dictionary");
        return NULL;
    }

    PyObject *m;
    if (PyDict_CheckExact(modules)) {
        m = PyDict_GetItemWithError(modules, name);
    }
    else {
        m = PyObject_GetItem(modules, name);
        // For backward-compatibility we copy the behavior
        // of PyDict_GetItemWithError().
        if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
            _PyErr_Clear(tstate);
        }
    }
    if (_PyErr_Occurred(tstate)) {
        return NULL;
    }
    if (m != NULL && PyModule_Check(m)) {
        return m;
    }
    m = PyModule_NewObject(name);
    if (m == NULL)
        return NULL;
    if (PyObject_SetItem(modules, name, m) != 0) {
        Py_DECREF(m);
        return NULL;
    }
    Py_DECREF(m); /* Yes, it still exists, in modules! */

    return m;
}

PyObject *
PyImport_AddModuleObject(PyObject *name)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return import_add_module(tstate, name);
}


PyObject *
PyImport_AddModule(const char *name)
{
    PyObject *nameobj = PyUnicode_FromString(name);
    if (nameobj == NULL) {
        return NULL;
    }
    PyObject *module = PyImport_AddModuleObject(nameobj);
    Py_DECREF(nameobj);
    return module;
}


/* Remove name from sys.modules, if it's there. */
static void
remove_module(PyThreadState *tstate, PyObject *name)
{
    PyObject *type, *value, *traceback;
    _PyErr_Fetch(tstate, &type, &value, &traceback);

    PyObject *modules = tstate->interp->modules;
    if (!PyMapping_HasKey(modules, name)) {
        goto out;
    }
    if (PyMapping_DelItem(modules, name) < 0) {
        _PyErr_SetString(tstate, PyExc_RuntimeError,
                         "deleting key in sys.modules failed");
        _PyErr_ChainExceptions(type, value, traceback);
        return;
    }

out:
    _PyErr_Restore(tstate, type, value, traceback);
}


/* Execute a code object in a module and return the module object
 * WITH INCREMENTED REFERENCE COUNT.  If an error occurs, name is
 * removed from sys.modules, to avoid leaving damaged module objects
 * in sys.modules.  The caller may wish to restore the original
 * module object (if any) in this case; PyImport_ReloadModule is an
 * example.
 *
 * Note that PyImport_ExecCodeModuleWithPathnames() is the preferred, richer
 * interface.  The other two exist primarily for backward compatibility.
 */
PyObject *
PyImport_ExecCodeModule(const char *name, PyObject *co)
{
    return PyImport_ExecCodeModuleWithPathnames(
        name, co, (char *)NULL, (char *)NULL);
}

PyObject *
PyImport_ExecCodeModuleEx(const char *name, PyObject *co, const char *pathname)
{
    return PyImport_ExecCodeModuleWithPathnames(
        name, co, pathname, (char *)NULL);
}

PyObject *
PyImport_ExecCodeModuleWithPathnames(const char *name, PyObject *co,
                                     const char *pathname,
                                     const char *cpathname)
{
    PyObject *m = NULL;
    PyObject *nameobj, *pathobj = NULL, *cpathobj = NULL, *external= NULL;

    nameobj = PyUnicode_FromString(name);
    if (nameobj == NULL)
        return NULL;

    if (cpathname != NULL) {
        cpathobj = PyUnicode_DecodeFSDefault(cpathname);
        if (cpathobj == NULL)
            goto error;
    }
    else
        cpathobj = NULL;

    if (pathname != NULL) {
        pathobj = PyUnicode_DecodeFSDefault(pathname);
        if (pathobj == NULL)
            goto error;
    }
    else if (cpathobj != NULL) {
        PyInterpreterState *interp = _PyInterpreterState_GET();
        _Py_IDENTIFIER(_get_sourcefile);

        if (interp == NULL) {
            Py_FatalError("no current interpreter");
        }

        external= PyObject_GetAttrString(interp->importlib,
                                         "_bootstrap_external");
        if (external != NULL) {
            pathobj = _PyObject_CallMethodIdOneArg(
                external, &PyId__get_sourcefile, cpathobj);
            Py_DECREF(external);
        }
        if (pathobj == NULL)
            PyErr_Clear();
    }
    else
        pathobj = NULL;

    m = PyImport_ExecCodeModuleObject(nameobj, co, pathobj, cpathobj);
error:
    Py_DECREF(nameobj);
    Py_XDECREF(pathobj);
    Py_XDECREF(cpathobj);
    return m;
}

static PyObject *
module_dict_for_exec(PyThreadState *tstate, PyObject *name)
{
    _Py_IDENTIFIER(__builtins__);
    PyObject *m, *d = NULL;

    m = import_add_module(tstate, name);
    if (m == NULL)
        return NULL;
    /* If the module is being reloaded, we get the old module back
       and re-use its dict to exec the new code. */
    d = PyModule_GetDict(m);
    if (_PyDict_GetItemIdWithError(d, &PyId___builtins__) == NULL) {
        if (_PyErr_Occurred(tstate) ||
            _PyDict_SetItemId(d, &PyId___builtins__,
                              PyEval_GetBuiltins()) != 0)
        {
            remove_module(tstate, name);
            return NULL;
        }
    }

    return d;  /* Return a borrowed reference. */
}

static PyObject *
exec_code_in_module(PyThreadState *tstate, PyObject *name,
                    PyObject *module_dict, PyObject *code_object)
{
    PyObject *v, *m;

    v = PyEval_EvalCode(code_object, module_dict, module_dict);
    if (v == NULL) {
        remove_module(tstate, name);
        return NULL;
    }
    Py_DECREF(v);

    m = import_get_module(tstate, name);
    if (m == NULL && !_PyErr_Occurred(tstate)) {
        _PyErr_Format(tstate, PyExc_ImportError,
                      "Loaded module %R not found in sys.modules",
                      name);
    }

    return m;
}

PyObject*
PyImport_ExecCodeModuleObject(PyObject *name, PyObject *co, PyObject *pathname,
                              PyObject *cpathname)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *d, *external, *res;
    _Py_IDENTIFIER(_fix_up_module);

    d = module_dict_for_exec(tstate, name);
    if (d == NULL) {
        return NULL;
    }

    if (pathname == NULL) {
        pathname = ((PyCodeObject *)co)->co_filename;
    }
    external = PyObject_GetAttrString(tstate->interp->importlib,
                                      "_bootstrap_external");
    if (external == NULL)
        return NULL;
    res = _PyObject_CallMethodIdObjArgs(external,
                                        &PyId__fix_up_module,
                                        d, name, pathname, cpathname, NULL);
    Py_DECREF(external);
    if (res != NULL) {
        Py_DECREF(res);
        res = exec_code_in_module(tstate, name, d, co);
    }
    return res;
}


static void
update_code_filenames(PyCodeObject *co, PyObject *oldname, PyObject *newname)
{
    PyObject *constants, *tmp;
    Py_ssize_t i, n;

    if (PyUnicode_Compare(co->co_filename, oldname))
        return;

    Py_INCREF(newname);
    Py_XSETREF(co->co_filename, newname);

    constants = co->co_consts;
    n = PyTuple_GET_SIZE(constants);
    for (i = 0; i < n; i++) {
        tmp = PyTuple_GET_ITEM(constants, i);
        if (PyCode_Check(tmp))
            update_code_filenames((PyCodeObject *)tmp,
                                  oldname, newname);
    }
}

static void
update_compiled_module(PyCodeObject *co, PyObject *newname)
{
    PyObject *oldname;

    if (PyUnicode_Compare(co->co_filename, newname) == 0)
        return;

    oldname = co->co_filename;
    Py_INCREF(oldname);
    update_code_filenames(co, oldname, newname);
    Py_DECREF(oldname);
}

/*[clinic input]
_imp._fix_co_filename

    code: object(type="PyCodeObject *", subclass_of="&PyCode_Type")
        Code object to change.

    path: unicode
        File path to use.
    /

Changes code.co_filename to specify the passed-in file path.
[clinic start generated code]*/

static PyObject *
_imp__fix_co_filename_impl(PyObject *module, PyCodeObject *code,
                           PyObject *path)
/*[clinic end generated code: output=1d002f100235587d input=895ba50e78b82f05]*/

{
    update_compiled_module(code, path);

    Py_RETURN_NONE;
}


/* Forward */
static const struct _frozen * find_frozen(PyObject *);


/* Helper to test for built-in module */

static int
is_builtin(PyObject *name)
{
    int i;
    for (i = 0; PyImport_Inittab[i].name != NULL; i++) {
        if (_PyUnicode_EqualToASCIIString(name, PyImport_Inittab[i].name)) {
            if (PyImport_Inittab[i].initfunc == NULL)
                return -1;
            else
                return 1;
        }
    }
    return 0;
}


/* Return a finder object for a sys.path/pkg.__path__ item 'p',
   possibly by fetching it from the path_importer_cache dict. If it
   wasn't yet cached, traverse path_hooks until a hook is found
   that can handle the path item. Return None if no hook could;
   this tells our caller that the path based finder could not find
   a finder for this path item. Cache the result in
   path_importer_cache.
   Returns a borrowed reference. */

static PyObject *
get_path_importer(PyThreadState *tstate, PyObject *path_importer_cache,
                  PyObject *path_hooks, PyObject *p)
{
    PyObject *importer;
    Py_ssize_t j, nhooks;

    /* These conditions are the caller's responsibility: */
    assert(PyList_Check(path_hooks));
    assert(PyDict_Check(path_importer_cache));

    nhooks = PyList_Size(path_hooks);
    if (nhooks < 0)
        return NULL; /* Shouldn't happen */

    importer = PyDict_GetItemWithError(path_importer_cache, p);
    if (importer != NULL || _PyErr_Occurred(tstate))
        return importer;

    /* set path_importer_cache[p] to None to avoid recursion */
    if (PyDict_SetItem(path_importer_cache, p, Py_None) != 0)
        return NULL;

    for (j = 0; j < nhooks; j++) {
        PyObject *hook = PyList_GetItem(path_hooks, j);
        if (hook == NULL)
            return NULL;
        importer = PyObject_CallOneArg(hook, p);
        if (importer != NULL)
            break;

        if (!_PyErr_ExceptionMatches(tstate, PyExc_ImportError)) {
            return NULL;
        }
        _PyErr_Clear(tstate);
    }
    if (importer == NULL) {
        return Py_None;
    }
    if (importer != NULL) {
        int err = PyDict_SetItem(path_importer_cache, p, importer);
        Py_DECREF(importer);
        if (err != 0)
            return NULL;
    }
    return importer;
}

PyObject *
PyImport_GetImporter(PyObject *path)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *importer=NULL, *path_importer_cache=NULL, *path_hooks=NULL;

    path_importer_cache = PySys_GetObject("path_importer_cache");
    path_hooks = PySys_GetObject("path_hooks");
    if (path_importer_cache != NULL && path_hooks != NULL) {
        importer = get_path_importer(tstate, path_importer_cache,
                                     path_hooks, path);
    }
    Py_XINCREF(importer); /* get_path_importer returns a borrowed reference */
    return importer;
}

/*[clinic input]
_imp.create_builtin

    spec: object
    /

Create an extension module.
[clinic start generated code]*/

static PyObject *
_imp_create_builtin(PyObject *module, PyObject *spec)
/*[clinic end generated code: output=ace7ff22271e6f39 input=37f966f890384e47]*/
{
    PyThreadState *tstate = _PyThreadState_GET();
    struct _inittab *p;
    PyObject *name;
    const char *namestr;
    PyObject *mod;

    name = PyObject_GetAttrString(spec, "name");
    if (name == NULL) {
        return NULL;
    }

    mod = _PyImport_FindExtensionObject(name, name);
    if (mod || _PyErr_Occurred(tstate)) {
        Py_DECREF(name);
        Py_XINCREF(mod);
        return mod;
    }

    namestr = PyUnicode_AsUTF8(name);
    if (namestr == NULL) {
        Py_DECREF(name);
        return NULL;
    }

    PyObject *modules = tstate->interp->modules;
    for (p = PyImport_Inittab; p->name != NULL; p++) {
        PyModuleDef *def;
        if (_PyUnicode_EqualToASCIIString(name, p->name)) {
            if (p->initfunc == NULL) {
                /* Cannot re-init internal module ("sys" or "builtins") */
                mod = PyImport_AddModule(namestr);
                Py_DECREF(name);
                return mod;
            }
            mod = (*p->initfunc)();
            if (mod == NULL) {
                Py_DECREF(name);
                return NULL;
            }
            if (PyObject_TypeCheck(mod, &PyModuleDef_Type)) {
                Py_DECREF(name);
                return PyModule_FromDefAndSpec((PyModuleDef*)mod, spec);
            } else {
                /* Remember pointer to module init function. */
                def = PyModule_GetDef(mod);
                if (def == NULL) {
                    Py_DECREF(name);
                    return NULL;
                }
                def->m_base.m_init = p->initfunc;
                if (_PyImport_FixupExtensionObject(mod, name, name,
                                                   modules) < 0) {
                    Py_DECREF(name);
                    return NULL;
                }
                Py_DECREF(name);
                return mod;
            }
        }
    }
    Py_DECREF(name);
    Py_RETURN_NONE;
}


/* Frozen modules */

static const struct _frozen *
find_frozen(PyObject *name)
{
    const struct _frozen *p;

    if (name == NULL)
        return NULL;

    for (p = PyImport_FrozenModules; ; p++) {
        if (p->name == NULL)
            return NULL;
        if (_PyUnicode_EqualToASCIIString(name, p->name))
            break;
    }
    return p;
}

static PyObject *
get_frozen_object(PyObject *name)
{
    const struct _frozen *p = find_frozen(name);
    int size;

    if (p == NULL) {
        PyErr_Format(PyExc_ImportError,
                     "No such frozen object named %R",
                     name);
        return NULL;
    }
    if (p->code == NULL) {
        PyErr_Format(PyExc_ImportError,
                     "Excluded frozen object named %R",
                     name);
        return NULL;
    }
    size = p->size;
    if (size < 0)
        size = -size;
    return PyMarshal_ReadObjectFromString((const char *)p->code, size);
}

static PyObject *
is_frozen_package(PyObject *name)
{
    const struct _frozen *p = find_frozen(name);
    int size;

    if (p == NULL) {
        PyErr_Format(PyExc_ImportError,
                     "No such frozen object named %R",
                     name);
        return NULL;
    }

    size = p->size;

    if (size < 0)
        Py_RETURN_TRUE;
    else
        Py_RETURN_FALSE;
}


/* Initialize a frozen module.
   Return 1 for success, 0 if the module is not found, and -1 with
   an exception set if the initialization failed.
   This function is also used from frozenmain.c */

int
PyImport_ImportFrozenModuleObject(PyObject *name)
{
    PyThreadState *tstate = _PyThreadState_GET();
    const struct _frozen *p;
    PyObject *co, *m, *d;
    int ispackage;
    int size;

    p = find_frozen(name);

    if (p == NULL)
        return 0;
    if (p->code == NULL) {
        _PyErr_Format(tstate, PyExc_ImportError,
                      "Excluded frozen object named %R",
                      name);
        return -1;
    }
    size = p->size;
    ispackage = (size < 0);
    if (ispackage)
        size = -size;
    co = PyMarshal_ReadObjectFromString((const char *)p->code, size);
    if (co == NULL)
        return -1;
    if (!PyCode_Check(co)) {
        _PyErr_Format(tstate, PyExc_TypeError,
                      "frozen object %R is not a code object",
                      name);
        goto err_return;
    }
    if (ispackage) {
        /* Set __path__ to the empty list */
        PyObject *l;
        int err;
        m = import_add_module(tstate, name);
        if (m == NULL)
            goto err_return;
        d = PyModule_GetDict(m);
        l = PyList_New(0);
        if (l == NULL) {
            goto err_return;
        }
        err = PyDict_SetItemString(d, "__path__", l);
        Py_DECREF(l);
        if (err != 0)
            goto err_return;
    }
    d = module_dict_for_exec(tstate, name);
    if (d == NULL) {
        goto err_return;
    }
    m = exec_code_in_module(tstate, name, d, co);
    if (m == NULL) {
        goto err_return;
    }
    Py_DECREF(co);
    Py_DECREF(m);
    return 1;

err_return:
    Py_DECREF(co);
    return -1;
}

int
PyImport_ImportFrozenModule(const char *name)
{
    PyObject *nameobj;
    int ret;
    nameobj = PyUnicode_InternFromString(name);
    if (nameobj == NULL)
        return -1;
    ret = PyImport_ImportFrozenModuleObject(nameobj);
    Py_DECREF(nameobj);
    return ret;
}


/* Import a module, either built-in, frozen, or external, and return
   its module object WITH INCREMENTED REFERENCE COUNT */

PyObject *
PyImport_ImportModule(const char *name)
{
    PyObject *pname;
    PyObject *result;

    pname = PyUnicode_FromString(name);
    if (pname == NULL)
        return NULL;
    result = PyImport_Import(pname);
    Py_DECREF(pname);
    return result;
}


/* Import a module without blocking
 *
 * At first it tries to fetch the module from sys.modules. If the module was
 * never loaded before it loads it with PyImport_ImportModule() unless another
 * thread holds the import lock. In the latter case the function raises an
 * ImportError instead of blocking.
 *
 * Returns the module object with incremented ref count.
 */
PyObject *
PyImport_ImportModuleNoBlock(const char *name)
{
    return PyImport_ImportModule(name);
}


/* Remove importlib frames from the traceback,
 * except in Verbose mode. */
static void
remove_importlib_frames(PyThreadState *tstate)
{
    const char *importlib_filename = "<frozen importlib._bootstrap>";
    const char *external_filename = "<frozen importlib._bootstrap_external>";
    const char *remove_frames = "_call_with_frames_removed";
    int always_trim = 0;
    int in_importlib = 0;
    PyObject *exception, *value, *base_tb, *tb;
    PyObject **prev_link, **outer_link = NULL;

    /* Synopsis: if it's an ImportError, we trim all importlib chunks
       from the traceback. We always trim chunks
       which end with a call to "_call_with_frames_removed". */

    _PyErr_Fetch(tstate, &exception, &value, &base_tb);
    if (!exception || _PyInterpreterState_GetConfig(tstate->interp)->verbose) {
        goto done;
    }

    if (PyType_IsSubtype((PyTypeObject *) exception,
                         (PyTypeObject *) PyExc_ImportError))
        always_trim = 1;

    prev_link = &base_tb;
    tb = base_tb;
    while (tb != NULL) {
        PyTracebackObject *traceback = (PyTracebackObject *)tb;
        PyObject *next = (PyObject *) traceback->tb_next;
        PyFrameObject *frame = traceback->tb_frame;
        PyCodeObject *code = PyFrame_GetCode(frame);
        int now_in_importlib;

        assert(PyTraceBack_Check(tb));
        now_in_importlib = _PyUnicode_EqualToASCIIString(code->co_filename, importlib_filename) ||
                           _PyUnicode_EqualToASCIIString(code->co_filename, external_filename);
        if (now_in_importlib && !in_importlib) {
            /* This is the link to this chunk of importlib tracebacks */
            outer_link = prev_link;
        }
        in_importlib = now_in_importlib;

        if (in_importlib &&
            (always_trim ||
             _PyUnicode_EqualToASCIIString(code->co_name, remove_frames))) {
            Py_XINCREF(next);
            Py_XSETREF(*outer_link, next);
            prev_link = outer_link;
        }
        else {
            prev_link = (PyObject **) &traceback->tb_next;
        }
        Py_DECREF(code);
        tb = next;
    }
done:
    _PyErr_Restore(tstate, exception, value, base_tb);
}


static PyObject *
resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level)
{
    _Py_IDENTIFIER(__package__);
    _Py_IDENTIFIER(__name__);
    _Py_IDENTIFIER(parent);
    PyObject *abs_name;
    PyObject *package = NULL;
    PyObject *spec;
    Py_ssize_t last_dot;
    PyObject *base;
    int level_up;

    if (globals == NULL) {
        _PyErr_SetString(tstate, PyExc_KeyError, "'__name__' not in globals");
        goto error;
    }
    if (!PyDict_Check(globals)) {
        _PyErr_SetString(tstate, PyExc_TypeError, "globals must be a dict");
        goto error;
    }
    package = _PyDict_GetItemIdWithError(globals, &PyId___package__);
    if (package == Py_None) {
        package = NULL;
    }
    else if (package == NULL && _PyErr_Occurred(tstate)) {
        goto error;
    }
    spec = _PyDict_GetItemIdWithError(globals, &PyId___spec__);
    if (spec == NULL && _PyErr_Occurred(tstate)) {
        goto error;
    }

    if (package != NULL) {
        Py_INCREF(package);
        if (!PyUnicode_Check(package)) {
            _PyErr_SetString(tstate, PyExc_TypeError,
                             "package must be a string");
            goto error;
        }
        else if (spec != NULL && spec != Py_None) {
            int equal;
            PyObject *parent = _PyObject_GetAttrId(spec, &PyId_parent);
            if (parent == NULL) {
                goto error;
            }

            equal = PyObject_RichCompareBool(package, parent, Py_EQ);
            Py_DECREF(parent);
            if (equal < 0) {
                goto error;
            }
            else if (equal == 0) {
                if (PyErr_WarnEx(PyExc_ImportWarning,
                        "__package__ != __spec__.parent", 1) < 0) {
                    goto error;
                }
            }
        }
    }
    else if (spec != NULL && spec != Py_None) {
        package = _PyObject_GetAttrId(spec, &PyId_parent);
        if (package == NULL) {
            goto error;
        }
        else if (!PyUnicode_Check(package)) {
            _PyErr_SetString(tstate, PyExc_TypeError,
                             "__spec__.parent must be a string");
            goto error;
        }
    }
    else {
        if (PyErr_WarnEx(PyExc_ImportWarning,
                    "can't resolve package from __spec__ or __package__, "
                    "falling back on __name__ and __path__", 1) < 0) {
            goto error;
        }

        package = _PyDict_GetItemIdWithError(globals, &PyId___name__);
        if (package == NULL) {
            if (!_PyErr_Occurred(tstate)) {
                _PyErr_SetString(tstate, PyExc_KeyError,
                                 "'__name__' not in globals");
            }
            goto error;
        }

        Py_INCREF(package);
        if (!PyUnicode_Check(package)) {
            _PyErr_SetString(tstate, PyExc_TypeError,
                             "__name__ must be a string");
            goto error;
        }

        if (_PyDict_GetItemIdWithError(globals, &PyId___path__) == NULL) {
            Py_ssize_t dot;

            if (_PyErr_Occurred(tstate) || PyUnicode_READY(package) < 0) {
                goto error;
            }

            dot = PyUnicode_FindChar(package, '.',
                                        0, PyUnicode_GET_LENGTH(package), -1);
            if (dot == -2) {
                goto error;
            }
            else if (dot == -1) {
                goto no_parent_error;
            }
            PyObject *substr = PyUnicode_Substring(package, 0, dot);
            if (substr == NULL) {
                goto error;
            }
            Py_SETREF(package, substr);
        }
    }

    last_dot = PyUnicode_GET_LENGTH(package);
    if (last_dot == 0) {
        goto no_parent_error;
    }

    for (level_up = 1; level_up < level; level_up += 1) {
        last_dot = PyUnicode_FindChar(package, '.', 0, last_dot, -1);
        if (last_dot == -2) {
            goto error;
        }
        else if (last_dot == -1) {
            _PyErr_SetString(tstate, PyExc_ImportError,
                             "attempted relative import beyond top-level "
                             "package");
            goto error;
        }
    }

    base = PyUnicode_Substring(package, 0, last_dot);
    Py_DECREF(package);
    if (base == NULL || PyUnicode_GET_LENGTH(name) == 0) {
        return base;
    }

    abs_name = PyUnicode_FromFormat("%U.%U", base, name);
    Py_DECREF(base);
    return abs_name;

  no_parent_error:
    _PyErr_SetString(tstate, PyExc_ImportError,
                     "attempted relative import "
                     "with no known parent package");

  error:
    Py_XDECREF(package);
    return NULL;
}

static PyObject *
import_find_and_load(PyThreadState *tstate, PyObject *abs_name)
{
    _Py_IDENTIFIER(_find_and_load);
    PyObject *mod = NULL;
    PyInterpreterState *interp = tstate->interp;
    int import_time = _PyInterpreterState_GetConfig(interp)->import_time;
    static int import_level;
    static _PyTime_t accumulated;

    _PyTime_t t1 = 0, accumulated_copy = accumulated;

    PyObject *sys_path = PySys_GetObject("path");
    PyObject *sys_meta_path = PySys_GetObject("meta_path");
    PyObject *sys_path_hooks = PySys_GetObject("path_hooks");
    if (_PySys_Audit(tstate, "import", "OOOOO",
                     abs_name, Py_None, sys_path ? sys_path : Py_None,
                     sys_meta_path ? sys_meta_path : Py_None,
                     sys_path_hooks ? sys_path_hooks : Py_None) < 0) {
        return NULL;
    }


    /* XOptions is initialized after first some imports.
     * So we can't have negative cache before completed initialization.
     * Anyway, importlib._find_and_load is much slower than
     * _PyDict_GetItemIdWithError().
     */
    if (import_time) {
        static int header = 1;
        if (header) {
            fputs("import time: self [us] | cumulative | imported package\n",
                  stderr);
            header = 0;
        }

        import_level++;
        t1 = _PyTime_GetPerfCounter();
        accumulated = 0;
    }

    if (PyDTrace_IMPORT_FIND_LOAD_START_ENABLED())
        PyDTrace_IMPORT_FIND_LOAD_START(PyUnicode_AsUTF8(abs_name));

    mod = _PyObject_CallMethodIdObjArgs(interp->importlib,
                                        &PyId__find_and_load, abs_name,
                                        interp->import_func, NULL);

    if (PyDTrace_IMPORT_FIND_LOAD_DONE_ENABLED())
        PyDTrace_IMPORT_FIND_LOAD_DONE(PyUnicode_AsUTF8(abs_name),
                                       mod != NULL);

    if (import_time) {
        _PyTime_t cum = _PyTime_GetPerfCounter() - t1;

        import_level--;
        fprintf(stderr, "import time: %9ld | %10ld | %*s%s\n",
                (long)_PyTime_AsMicroseconds(cum - accumulated, _PyTime_ROUND_CEILING),
                (long)_PyTime_AsMicroseconds(cum, _PyTime_ROUND_CEILING),
                import_level*2, "", PyUnicode_AsUTF8(abs_name));

        accumulated = accumulated_copy + cum;
    }

    return mod;
}

PyObject *
PyImport_GetModule(PyObject *name)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *mod;

    mod = import_get_module(tstate, name);
    if (mod != NULL && mod != Py_None) {
        if (import_ensure_initialized(tstate, mod, name) < 0) {
            Py_DECREF(mod);
            remove_importlib_frames(tstate);
            return NULL;
        }
    }
    return mod;
}

PyObject *
PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                                 PyObject *locals, PyObject *fromlist,
                                 int level)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _Py_IDENTIFIER(_handle_fromlist);
    PyObject *abs_name = NULL;
    PyObject *final_mod = NULL;
    PyObject *mod = NULL;
    PyObject *package = NULL;
    PyInterpreterState *interp = tstate->interp;
    int has_from;

    if (name == NULL) {
        _PyErr_SetString(tstate, PyExc_ValueError, "Empty module name");
        goto error;
    }

    /* The below code is importlib.__import__() & _gcd_import(), ported to C
       for added performance. */

    if (!PyUnicode_Check(name)) {
        _PyErr_SetString(tstate, PyExc_TypeError,
                         "module name must be a string");
        goto error;
    }
    if (PyUnicode_READY(name) < 0) {
        goto error;
    }
    if (level < 0) {
        _PyErr_SetString(tstate, PyExc_ValueError, "level must be >= 0");
        goto error;
    }

    if (level > 0) {
        abs_name = resolve_name(tstate, name, globals, level);
        if (abs_name == NULL)
            goto error;
    }
    else {  /* level == 0 */
        if (PyUnicode_GET_LENGTH(name) == 0) {
            _PyErr_SetString(tstate, PyExc_ValueError, "Empty module name");
            goto error;
        }
        abs_name = name;
        Py_INCREF(abs_name);
    }

    mod = import_get_module(tstate, abs_name);
    if (mod == NULL && _PyErr_Occurred(tstate)) {
        goto error;
    }

    if (mod != NULL && mod != Py_None) {
        if (import_ensure_initialized(tstate, mod, name) < 0) {
            goto error;
        }
    }
    else {
        Py_XDECREF(mod);
        mod = import_find_and_load(tstate, abs_name);
        if (mod == NULL) {
            goto error;
        }
    }

    has_from = 0;
    if (fromlist != NULL && fromlist != Py_None) {
        has_from = PyObject_IsTrue(fromlist);
        if (has_from < 0)
            goto error;
    }
    if (!has_from) {
        Py_ssize_t len = PyUnicode_GET_LENGTH(name);
        if (level == 0 || len > 0) {
            Py_ssize_t dot;

            dot = PyUnicode_FindChar(name, '.', 0, len, 1);
            if (dot == -2) {
                goto error;
            }

            if (dot == -1) {
                /* No dot in module name, simple exit */
                final_mod = mod;
                Py_INCREF(mod);
                goto error;
            }

            if (level == 0) {
                PyObject *front = PyUnicode_Substring(name, 0, dot);
                if (front == NULL) {
                    goto error;
                }

                final_mod = PyImport_ImportModuleLevelObject(front, NULL, NULL, NULL, 0);
                Py_DECREF(front);
            }
            else {
                Py_ssize_t cut_off = len - dot;
                Py_ssize_t abs_name_len = PyUnicode_GET_LENGTH(abs_name);
                PyObject *to_return = PyUnicode_Substring(abs_name, 0,
                                                        abs_name_len - cut_off);
                if (to_return == NULL) {
                    goto error;
                }

                final_mod = import_get_module(tstate, to_return);
                Py_DECREF(to_return);
                if (final_mod == NULL) {
                    if (!_PyErr_Occurred(tstate)) {
                        _PyErr_Format(tstate, PyExc_KeyError,
                                      "%R not in sys.modules as expected",
                                      to_return);
                    }
                    goto error;
                }
            }
        }
        else {
            final_mod = mod;
            Py_INCREF(mod);
        }
    }
    else {
        PyObject *path;
        if (_PyObject_LookupAttrId(mod, &PyId___path__, &path) < 0) {
            goto error;
        }
        if (path) {
            Py_DECREF(path);
            final_mod = _PyObject_CallMethodIdObjArgs(
                        interp->importlib, &PyId__handle_fromlist,
                        mod, fromlist, interp->import_func, NULL);
        }
        else {
            final_mod = mod;
            Py_INCREF(mod);
        }
    }

  error:
    Py_XDECREF(abs_name);
    Py_XDECREF(mod);
    Py_XDECREF(package);
    if (final_mod == NULL) {
        remove_importlib_frames(tstate);
    }
    return final_mod;
}

PyObject *
PyImport_ImportModuleLevel(const char *name, PyObject *globals, PyObject *locals,
                           PyObject *fromlist, int level)
{
    PyObject *nameobj, *mod;
    nameobj = PyUnicode_FromString(name);
    if (nameobj == NULL)
        return NULL;
    mod = PyImport_ImportModuleLevelObject(nameobj, globals, locals,
                                           fromlist, level);
    Py_DECREF(nameobj);
    return mod;
}


/* Re-import a module of any kind and return its module object, WITH
   INCREMENTED REFERENCE COUNT */

PyObject *
PyImport_ReloadModule(PyObject *m)
{
    _Py_IDENTIFIER(importlib);
    _Py_IDENTIFIER(reload);
    PyObject *reloaded_module = NULL;
    PyObject *importlib = _PyImport_GetModuleId(&PyId_importlib);
    if (importlib == NULL) {
        if (PyErr_Occurred()) {
            return NULL;
        }

        importlib = PyImport_ImportModule("importlib");
        if (importlib == NULL) {
            return NULL;
        }
    }

    reloaded_module = _PyObject_CallMethodIdOneArg(importlib, &PyId_reload, m);
    Py_DECREF(importlib);
    return reloaded_module;
}


/* Higher-level import emulator which emulates the "import" statement
   more accurately -- it invokes the __import__() function from the
   builtins of the current globals.  This means that the import is
   done using whatever import hooks are installed in the current
   environment.
   A dummy list ["__doc__"] is passed as the 4th argument so that
   e.g. PyImport_Import(PyUnicode_FromString("win32com.client.gencache"))
   will return <module "gencache"> instead of <module "win32com">. */

PyObject *
PyImport_Import(PyObject *module_name)
{
    PyThreadState *tstate = _PyThreadState_GET();
    static PyObject *silly_list = NULL;
    static PyObject *builtins_str = NULL;
    static PyObject *import_str = NULL;
    PyObject *globals = NULL;
    PyObject *import = NULL;
    PyObject *builtins = NULL;
    PyObject *r = NULL;

    /* Initialize constant string objects */
    if (silly_list == NULL) {
        import_str = PyUnicode_InternFromString("__import__");
        if (import_str == NULL)
            return NULL;
        builtins_str = PyUnicode_InternFromString("__builtins__");
        if (builtins_str == NULL)
            return NULL;
        silly_list = PyList_New(0);
        if (silly_list == NULL)
            return NULL;
    }

    /* Get the builtins from current globals */
    globals = PyEval_GetGlobals();
    if (globals != NULL) {
        Py_INCREF(globals);
        builtins = PyObject_GetItem(globals, builtins_str);
        if (builtins == NULL)
            goto err;
    }
    else {
        /* No globals -- use standard builtins, and fake globals */
        builtins = PyImport_ImportModuleLevel("builtins",
                                              NULL, NULL, NULL, 0);
        if (builtins == NULL)
            return NULL;
        globals = Py_BuildValue("{OO}", builtins_str, builtins);
        if (globals == NULL)
            goto err;
    }

    /* Get the __import__ function from the builtins */
    if (PyDict_Check(builtins)) {
        import = PyObject_GetItem(builtins, import_str);
        if (import == NULL) {
            _PyErr_SetObject(tstate, PyExc_KeyError, import_str);
        }
    }
    else
        import = PyObject_GetAttr(builtins, import_str);
    if (import == NULL)
        goto err;

    /* Call the __import__ function with the proper argument list
       Always use absolute import here.
       Calling for side-effect of import. */
    r = PyObject_CallFunction(import, "OOOOi", module_name, globals,
                              globals, silly_list, 0, NULL);
    if (r == NULL)
        goto err;
    Py_DECREF(r);

    r = import_get_module(tstate, module_name);
    if (r == NULL && !_PyErr_Occurred(tstate)) {
        _PyErr_SetObject(tstate, PyExc_KeyError, module_name);
    }

  err:
    Py_XDECREF(globals);
    Py_XDECREF(builtins);
    Py_XDECREF(import);

    return r;
}

/*[clinic input]
_imp.extension_suffixes

Returns the list of file suffixes used to identify extension modules.
[clinic start generated code]*/

static PyObject *
_imp_extension_suffixes_impl(PyObject *module)
/*[clinic end generated code: output=0bf346e25a8f0cd3 input=ecdeeecfcb6f839e]*/
{
    PyObject *list;

    list = PyList_New(0);
    if (list == NULL)
        return NULL;
#ifdef HAVE_DYNAMIC_LOADING
    const char *suffix;
    unsigned int index = 0;

    while ((suffix = _PyImport_DynLoadFiletab[index])) {
        PyObject *item = PyUnicode_FromString(suffix);
        if (item == NULL) {
            Py_DECREF(list);
            return NULL;
        }
        if (PyList_Append(list, item) < 0) {
            Py_DECREF(list);
            Py_DECREF(item);
            return NULL;
        }
        Py_DECREF(item);
        index += 1;
    }
#endif
    return list;
}

/*[clinic input]
_imp.init_frozen

    name: unicode
    /

Initializes a frozen module.
[clinic start generated code]*/

static PyObject *
_imp_init_frozen_impl(PyObject *module, PyObject *name)
/*[clinic end generated code: output=fc0511ed869fd69c input=13019adfc04f3fb3]*/
{
    PyThreadState *tstate = _PyThreadState_GET();
    int ret;
    PyObject *m;

    ret = PyImport_ImportFrozenModuleObject(name);
    if (ret < 0)
        return NULL;
    if (ret == 0) {
        Py_RETURN_NONE;
    }
    m = import_add_module(tstate, name);
    Py_XINCREF(m);
    return m;
}

/*[clinic input]
_imp.get_frozen_object

    name: unicode
    /

Create a code object for a frozen module.
[clinic start generated code]*/

static PyObject *
_imp_get_frozen_object_impl(PyObject *module, PyObject *name)
/*[clinic end generated code: output=2568cc5b7aa0da63 input=ed689bc05358fdbd]*/
{
    return get_frozen_object(name);
}

/*[clinic input]
_imp.is_frozen_package

    name: unicode
    /

Returns True if the module name is of a frozen package.
[clinic start generated code]*/

static PyObject *
_imp_is_frozen_package_impl(PyObject *module, PyObject *name)
/*[clinic end generated code: output=e70cbdb45784a1c9 input=81b6cdecd080fbb8]*/
{
    return is_frozen_package(name);
}

/*[clinic input]
_imp.is_builtin

    name: unicode
    /

Returns True if the module name corresponds to a built-in module.
[clinic start generated code]*/

static PyObject *
_imp_is_builtin_impl(PyObject *module, PyObject *name)
/*[clinic end generated code: output=3bfd1162e2d3be82 input=86befdac021dd1c7]*/
{
    return PyLong_FromLong(is_builtin(name));
}

/*[clinic input]
_imp.is_frozen

    name: unicode
    /

Returns True if the module name corresponds to a frozen module.
[clinic start generated code]*/

static PyObject *
_imp_is_frozen_impl(PyObject *module, PyObject *name)
/*[clinic end generated code: output=01f408f5ec0f2577 input=7301dbca1897d66b]*/
{
    const struct _frozen *p;

    p = find_frozen(name);
    return PyBool_FromLong((long) (p == NULL ? 0 : p->size));
}

/* Common implementation for _imp.exec_dynamic and _imp.exec_builtin */
static int
exec_builtin_or_dynamic(PyObject *mod) {
    PyModuleDef *def;
    void *state;

    if (!PyModule_Check(mod)) {
        return 0;
    }

    def = PyModule_GetDef(mod);
    if (def == NULL) {
        return 0;
    }

    state = PyModule_GetState(mod);
    if (state) {
        /* Already initialized; skip reload */
        return 0;
    }

    return PyModule_ExecDef(mod, def);
}

#ifdef HAVE_DYNAMIC_LOADING

/*[clinic input]
_imp.create_dynamic

    spec: object
    file: object = NULL
    /

Create an extension module.
[clinic start generated code]*/

static PyObject *
_imp_create_dynamic_impl(PyObject *module, PyObject *spec, PyObject *file)
/*[clinic end generated code: output=83249b827a4fde77 input=c31b954f4cf4e09d]*/
{
    PyObject *mod, *name, *path;
    FILE *fp;

    name = PyObject_GetAttrString(spec, "name");
    if (name == NULL) {
        return NULL;
    }

    path = PyObject_GetAttrString(spec, "origin");
    if (path == NULL) {
        Py_DECREF(name);
        return NULL;
    }

    mod = _PyImport_FindExtensionObject(name, path);
    if (mod != NULL || PyErr_Occurred()) {
        Py_DECREF(name);
        Py_DECREF(path);
        Py_XINCREF(mod);
        return mod;
    }

    if (file != NULL) {
        fp = _Py_fopen_obj(path, "r");
        if (fp == NULL) {
            Py_DECREF(name);
            Py_DECREF(path);
            return NULL;
        }
    }
    else
        fp = NULL;

    mod = _PyImport_LoadDynamicModuleWithSpec(spec, fp);

    Py_DECREF(name);
    Py_DECREF(path);
    if (fp)
        fclose(fp);
    return mod;
}

/*[clinic input]
_imp.exec_dynamic -> int

    mod: object
    /

Initialize an extension module.
[clinic start generated code]*/

static int
_imp_exec_dynamic_impl(PyObject *module, PyObject *mod)
/*[clinic end generated code: output=f5720ac7b465877d input=9fdbfcb250280d3a]*/
{
    return exec_builtin_or_dynamic(mod);
}


#endif /* HAVE_DYNAMIC_LOADING */

/*[clinic input]
_imp.exec_builtin -> int

    mod: object
    /

Initialize a built-in module.
[clinic start generated code]*/

static int
_imp_exec_builtin_impl(PyObject *module, PyObject *mod)
/*[clinic end generated code: output=0262447b240c038e input=7beed5a2f12a60ca]*/
{
    return exec_builtin_or_dynamic(mod);
}

/*[clinic input]
_imp.source_hash

    key: long
    source: Py_buffer
[clinic start generated code]*/

static PyObject *
_imp_source_hash_impl(PyObject *module, long key, Py_buffer *source)
/*[clinic end generated code: output=edb292448cf399ea input=9aaad1e590089789]*/
{
    union {
        uint64_t x;
        char data[sizeof(uint64_t)];
    } hash;
    hash.x = _Py_KeyedHash((uint64_t)key, source->buf, source->len);
#if !PY_LITTLE_ENDIAN
    // Force to little-endian. There really ought to be a succinct standard way
    // to do this.
    for (size_t i = 0; i < sizeof(hash.data)/2; i++) {
        char tmp = hash.data[i];
        hash.data[i] = hash.data[sizeof(hash.data) - i - 1];
        hash.data[sizeof(hash.data) - i - 1] = tmp;
    }
#endif
    return PyBytes_FromStringAndSize(hash.data, sizeof(hash.data));
}


PyDoc_STRVAR(doc_imp,
"(Extremely) low-level import machinery bits as used by importlib and imp.");

static PyMethodDef imp_methods[] = {
    _IMP_EXTENSION_SUFFIXES_METHODDEF
    _IMP_LOCK_HELD_METHODDEF
    _IMP_ACQUIRE_LOCK_METHODDEF
    _IMP_RELEASE_LOCK_METHODDEF
    _IMP_GET_FROZEN_OBJECT_METHODDEF
    _IMP_IS_FROZEN_PACKAGE_METHODDEF
    _IMP_CREATE_BUILTIN_METHODDEF
    _IMP_INIT_FROZEN_METHODDEF
    _IMP_IS_BUILTIN_METHODDEF
    _IMP_IS_FROZEN_METHODDEF
    _IMP_CREATE_DYNAMIC_METHODDEF
    _IMP_EXEC_DYNAMIC_METHODDEF
    _IMP_EXEC_BUILTIN_METHODDEF
    _IMP__FIX_CO_FILENAME_METHODDEF
    _IMP_SOURCE_HASH_METHODDEF
    {NULL, NULL}  /* sentinel */
};


static struct PyModuleDef impmodule = {
    PyModuleDef_HEAD_INIT,
    "_imp",
    doc_imp,
    0,
    imp_methods,
    NULL,
    NULL,
    NULL,
    NULL
};

PyMODINIT_FUNC
PyInit__imp(void)
{
    PyObject *m, *d;

    m = PyModule_Create(&impmodule);
    if (m == NULL) {
        goto failure;
    }
    d = PyModule_GetDict(m);
    if (d == NULL) {
        goto failure;
    }

    const wchar_t *mode = _Py_GetConfig()->check_hash_pycs_mode;
    PyObject *pyc_mode = PyUnicode_FromWideChar(mode, -1);
    if (pyc_mode == NULL) {
        goto failure;
    }
    if (PyDict_SetItemString(d, "check_hash_based_pycs", pyc_mode) < 0) {
        Py_DECREF(pyc_mode);
        goto failure;
    }
    Py_DECREF(pyc_mode);

    return m;
  failure:
    Py_XDECREF(m);
    return NULL;
}


/* API for embedding applications that want to add their own entries
   to the table of built-in modules.  This should normally be called
   *before* Py_Initialize().  When the table resize fails, -1 is
   returned and the existing table is unchanged.

   After a similar function by Just van Rossum. */

int
PyImport_ExtendInittab(struct _inittab *newtab)
{
    struct _inittab *p;
    size_t i, n;
    int res = 0;

    /* Count the number of entries in both tables */
    for (n = 0; newtab[n].name != NULL; n++)
        ;
    if (n == 0)
        return 0; /* Nothing to do */
    for (i = 0; PyImport_Inittab[i].name != NULL; i++)
        ;

    /* Force default raw memory allocator to get a known allocator to be able
       to release the memory in _PyImport_Fini2() */
    PyMemAllocatorEx old_alloc;
    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);

    /* Allocate new memory for the combined table */
    p = NULL;
    if (i + n <= SIZE_MAX / sizeof(struct _inittab) - 1) {
        size_t size = sizeof(struct _inittab) * (i + n + 1);
        p = PyMem_RawRealloc(inittab_copy, size);
    }
    if (p == NULL) {
        res = -1;
        goto done;
    }

    /* Copy the tables into the new memory at the first call
       to PyImport_ExtendInittab(). */
    if (inittab_copy != PyImport_Inittab) {
        memcpy(p, PyImport_Inittab, (i+1) * sizeof(struct _inittab));
    }
    memcpy(p + i, newtab, (n + 1) * sizeof(struct _inittab));
    PyImport_Inittab = inittab_copy = p;

done:
    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
    return res;
}

/* Shorthand to add a single entry given a name and a function */

int
PyImport_AppendInittab(const char *name, PyObject* (*initfunc)(void))
{
    struct _inittab newtab[2];

    memset(newtab, '\0', sizeof newtab);

    newtab[0].name = name;
    newtab[0].initfunc = initfunc;

    return PyImport_ExtendInittab(newtab);
}

#ifdef __cplusplus
}
#endif