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;