import.c

/* Module definition and import implementation */

#include "Python.h"

#include "Python-ast.h"
#undef Yield /* undefine macro conflicting with winbase.h */
#include "errcode.h"
#include "marshal.h"
#include "code.h"
#include "frameobject.h"
#include "osdefs.h"
#include "importdl.h"

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

#define CACHEDIR "__pycache__"

/* 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 PyObject *initstr = NULL;

/* Initialize things */

void
_PyImport_Init(void)
{
    initstr = PyUnicode_InternFromString("__init__");
    if (initstr == NULL)
        Py_FatalError("Can't initialize import variables");
}

void
_PyImportHooks_Init(void)
{
    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) {
  error:
    PyErr_Print();
    Py_FatalError("initializing sys.meta_path, sys.path_hooks, "
                  "or path_importer_cache failed");
    }
    Py_DECREF(path_hooks);
}

void
_PyImportZip_Init(void)
{
    PyObject *path_hooks, *zimpimport;
    int err = 0;

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

    if (Py_VerboseFlag)
        PySys_WriteStderr("# installing zipimport hook\n");

    zimpimport = PyImport_ImportModule("zipimport");
    if (zimpimport == NULL) {
        PyErr_Clear(); /* No zip import module -- okay */
        if (Py_VerboseFlag)
            PySys_WriteStderr("# can't import zipimport\n");
    }
    else {
        _Py_IDENTIFIER(zipimporter);
        PyObject *zipimporter = _PyObject_GetAttrId(zimpimport,
                                                    &PyId_zipimporter);
        Py_DECREF(zimpimport);
        if (zipimporter == NULL) {
            PyErr_Clear(); /* No zipimporter object -- okay */
            if (Py_VerboseFlag)
                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 (Py_VerboseFlag)
                PySys_WriteStderr(
                    "# installed zipimport hook\n");
        }
    }

    return;

  error:
    PyErr_Print();
    Py_FatalError("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. */

#ifdef WITH_THREAD

#include "pythread.h"

static PyThread_type_lock import_lock = 0;
static long import_lock_thread = -1;
static int import_lock_level = 0;

void
_PyImport_AcquireLock(void)
{
    long me = PyThread_get_thread_ident();
    if (me == -1)
        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 != -1 || !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)
{
    long me = PyThread_get_thread_ident();
    if (me == -1 || 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 = -1;
        PyThread_release_lock(import_lock);
    }
    return 1;
}

/* This function is called from PyOS_AfterFork 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)
        import_lock = PyThread_allocate_lock();
    if (import_lock_level > 1) {
        /* Forked as a side effect of import */
        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 = -1;
        import_lock_level = 0;
    }
}

#endif

static PyObject *
imp_lock_held(PyObject *self, PyObject *noargs)
{
#ifdef WITH_THREAD
    return PyBool_FromLong(import_lock_thread != -1);
#else
    return PyBool_FromLong(0);
#endif
}

static PyObject *
imp_acquire_lock(PyObject *self, PyObject *noargs)
{
#ifdef WITH_THREAD
    _PyImport_AcquireLock();
#endif
    Py_INCREF(Py_None);
    return Py_None;
}

static PyObject *
imp_release_lock(PyObject *self, PyObject *noargs)
{
#ifdef WITH_THREAD
    if (_PyImport_ReleaseLock() < 0) {
        PyErr_SetString(PyExc_RuntimeError,
                        "not holding the import lock");
        return NULL;
    }
#endif
    Py_INCREF(Py_None);
    return Py_None;
}

void
_PyImport_Fini(void)
{
    Py_XDECREF(extensions);
    extensions = NULL;
#ifdef WITH_THREAD
    if (import_lock != NULL) {
        PyThread_free_lock(import_lock);
        import_lock = NULL;
    }
#endif
}

/* Helper for sys */

PyObject *
PyImport_GetModuleDict(void)
{
    PyInterpreterState *interp = PyThreadState_GET()->interp;
    if (interp->modules == NULL)
        Py_FatalError("PyImport_GetModuleDict: no module dictionary!");
    return interp->modules;
}


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

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

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

void
PyImport_Cleanup(void)
{
    Py_ssize_t pos;
    PyObject *key, *value, *dict;
    PyInterpreterState *interp = PyThreadState_GET()->interp;
    PyObject *modules = interp->modules;
    PyObject *builtins = interp->builtins;
    PyObject *weaklist = NULL;

    if (modules == NULL)
        return; /* Already done */

    /* 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? */

    value = PyDict_GetItemString(modules, "builtins");
    if (value != NULL && PyModule_Check(value)) {
        dict = PyModule_GetDict(value);
        if (Py_VerboseFlag)
            PySys_WriteStderr("# clear builtins._\n");
        PyDict_SetItemString(dict, "_", Py_None);
    }
    value = PyDict_GetItemString(modules, "sys");
    if (value != NULL && PyModule_Check(value)) {
        char **p;
        PyObject *v;
        dict = PyModule_GetDict(value);
        for (p = sys_deletes; *p != NULL; p++) {
            if (Py_VerboseFlag)
                PySys_WriteStderr("# clear sys.%s\n", *p);
            PyDict_SetItemString(dict, *p, Py_None);
        }
        for (p = sys_files; *p != NULL; p+=2) {
            if (Py_VerboseFlag)
                PySys_WriteStderr("# restore sys.%s\n", *p);
            v = PyDict_GetItemString(dict, *(p+1));
            if (v == NULL)
                v = Py_None;
            PyDict_SetItemString(dict, *p, v);
        }
    }

    /* 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. */
    weaklist = PyList_New(0);
    if (weaklist == NULL)
        PyErr_Clear();

#define STORE_MODULE_WEAKREF(name, mod) \
    if (weaklist != NULL) { \
        PyObject *wr = PyWeakref_NewRef(mod, NULL); \
        if (name && wr) { \
            PyObject *tup = PyTuple_Pack(2, name, wr); \
            PyList_Append(weaklist, tup); \
            Py_XDECREF(tup); \
        } \
        Py_XDECREF(wr); \
        if (PyErr_Occurred()) \
            PyErr_Clear(); \
    }

    /* Remove all modules from sys.modules, hoping that garbage collection
       can reclaim most of them. */
    pos = 0;
    while (PyDict_Next(modules, &pos, &key, &value)) {
        if (PyModule_Check(value)) {
            if (Py_VerboseFlag && PyUnicode_Check(key))
                PySys_FormatStderr("# cleanup[2] removing %U\n", key, value);
            STORE_MODULE_WEAKREF(key, value);
            PyDict_SetItem(modules, key, Py_None);
        }
    }

    /* Clear the modules dict. */
    PyDict_Clear(modules);
    /* Replace the interpreter's reference to builtins with an empty dict
       (module globals still have a reference to the original builtins). */
    builtins = interp->builtins;
    interp->builtins = PyDict_New();
    Py_DECREF(builtins);
    /* Clear module dict copies stored in the interpreter state */
    _PyState_ClearModules();
    /* Collect references */
    _PyGC_CollectNoFail();
    /* Dump GC stats before it's too late, since it uses the warnings
       machinery. */
    _PyGC_DumpShutdownStats();

    /* 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. */
    if (weaklist != NULL) {
        Py_ssize_t i, n;
        n = PyList_GET_SIZE(weaklist);
        for (i = 0; i < n; 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;
            Py_INCREF(mod);
            assert(PyModule_Check(mod));
            if (Py_VerboseFlag && PyUnicode_Check(name))
                PySys_FormatStderr("# cleanup[3] wiping %U\n",
                                   name, mod);
            _PyModule_Clear(mod);
            Py_DECREF(mod);
        }
        Py_DECREF(weaklist);
    }

    /* 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 STORE_MODULE_WEAKREF
}


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

long
PyImport_GetMagicNumber(void)
{
    long res;
    PyInterpreterState *interp = PyThreadState_Get()->interp;
    PyObject *pyc_magic = PyObject_GetAttrString(interp->importlib,
                                                 "_RAW_MAGIC_NUMBER");
    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, *dict, *key;
    struct PyModuleDef *def;
    int res;
    if (extensions == NULL) {
        extensions = PyDict_New();
        if (extensions == NULL)
            return -1;
    }
    if (mod == NULL || !PyModule_Check(mod)) {
        PyErr_BadInternalCall();
        return -1;
    }
    def = PyModule_GetDef(mod);
    if (!def) {
        PyErr_BadInternalCall();
        return -1;
    }
    modules = PyImport_GetModuleDict();
    if (PyDict_SetItem(modules, name, mod) < 0)
        return -1;
    if (_PyState_AddModule(mod, def) < 0) {
        PyDict_DelItem(modules, name);
        return -1;
    }
    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_DECREF(def->m_base.m_copy);
            def->m_base.m_copy = NULL;
        }
        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;
    }
    key = PyTuple_Pack(2, filename, name);
    if (key == NULL)
        return -1;
    res = PyDict_SetItem(extensions, key, (PyObject *)def);
    Py_DECREF(key);
    if (res < 0)
        return -1;
    return 0;
}

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

PyObject *
_PyImport_FindExtensionObject(PyObject *name, PyObject *filename)
{
    PyObject *mod, *mdict, *key;
    PyModuleDef* def;
    if (extensions == NULL)
        return NULL;
    key = PyTuple_Pack(2, filename, name);
    if (key == NULL)
        return NULL;
    def = (PyModuleDef *)PyDict_GetItem(extensions, key);
    Py_DECREF(key);
    if (def == NULL)
        return NULL;
    if (def->m_size == -1) {
        /* Module does not support repeated initialization */
        if (def->m_base.m_copy == NULL)
            return NULL;
        mod = PyImport_AddModuleObject(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 (PyDict_SetItem(PyImport_GetModuleDict(), name, mod) == -1) {
            Py_DECREF(mod);
            return NULL;
        }
        Py_DECREF(mod);
    }
    if (_PyState_AddModule(mod, def) < 0) {
        PyDict_DelItem(PyImport_GetModuleDict(), name);
        Py_DECREF(mod);
        return NULL;
    }
    if (Py_VerboseFlag)
        PySys_FormatStderr("import %U # previously loaded (%R)\n",
                          name, filename);
    return mod;

}

PyObject *
_PyImport_FindBuiltin(const char *name)
{
    PyObject *res, *nameobj;
    nameobj = PyUnicode_InternFromString(name);
    if (nameobj == NULL)
        return NULL;
    res = _PyImport_FindExtensionObject(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! */

PyObject *
PyImport_AddModuleObject(PyObject *name)
{
    PyObject *modules = PyImport_GetModuleDict();
    PyObject *m;

    if ((m = PyDict_GetItem(modules, name)) != NULL &&
        PyModule_Check(m))
        return m;
    m = PyModule_NewObject(name);
    if (m == NULL)
        return NULL;
    if (PyDict_SetItem(modules, name, m) != 0) {
        Py_DECREF(m);
        return NULL;
    }
    Py_DECREF(m); /* Yes, it still exists, in modules! */

    return m;
}

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


/* Remove name from sys.modules, if it's there. */
static void
remove_module(PyObject *name)
{
    PyObject *modules = PyImport_GetModuleDict();
    if (PyDict_GetItem(modules, name) == NULL)
        return;
    if (PyDict_DelItem(modules, name) < 0)
        Py_FatalError("import:  deleting existing key in"
                      "sys.modules failed");
}


/* 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(char *name, PyObject *co)
{
    return PyImport_ExecCodeModuleWithPathnames(
        name, co, (char *)NULL, (char *)NULL);
}

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

PyObject *
PyImport_ExecCodeModuleWithPathnames(char *name, PyObject *co, char *pathname,
                                     char *cpathname)
{
    PyObject *m = NULL;
    PyObject *nameobj, *pathobj = NULL, *cpathobj = 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 = PyThreadState_GET()->interp;
        _Py_IDENTIFIER(_get_sourcefile);

        if (interp == NULL) {
            Py_FatalError("PyImport_ExecCodeModuleWithPathnames: "
                          "no interpreter!");
        }

        pathobj = _PyObject_CallMethodIdObjArgs(interp->importlib,
                                                &PyId__get_sourcefile, cpathobj,
                                                NULL);
        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;
}

PyObject*
PyImport_ExecCodeModuleObject(PyObject *name, PyObject *co, PyObject *pathname,
                              PyObject *cpathname)
{
    PyObject *modules = PyImport_GetModuleDict();
    PyObject *m, *d, *v;

    m = PyImport_AddModuleObject(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_GetItemString(d, "__builtins__") == NULL) {
        if (PyDict_SetItemString(d, "__builtins__",
                                 PyEval_GetBuiltins()) != 0)
            goto error;
    }
    if (pathname != NULL) {
        v = pathname;
    }
    else {
        v = ((PyCodeObject *)co)->co_filename;
    }
    Py_INCREF(v);
    if (PyDict_SetItemString(d, "__file__", v) != 0)
        PyErr_Clear(); /* Not important enough to report */
    Py_DECREF(v);

    /* Remember the pyc path name as the __cached__ attribute. */
    if (cpathname != NULL)
        v = cpathname;
    else
        v = Py_None;
    if (PyDict_SetItemString(d, "__cached__", v) != 0)
        PyErr_Clear(); /* Not important enough to report */

    v = PyEval_EvalCode(co, d, d);
    if (v == NULL)
        goto error;
    Py_DECREF(v);

    if ((m = PyDict_GetItem(modules, name)) == NULL) {
        PyErr_Format(PyExc_ImportError,
                     "Loaded module %R not found in sys.modules",
                     name);
        return NULL;
    }

    Py_INCREF(m);

    return m;

  error:
    remove_module(name);
    return NULL;
}


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;

    tmp = co->co_filename;
    co->co_filename = newname;
    Py_INCREF(co->co_filename);
    Py_DECREF(tmp);

    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);
}

static PyObject *
imp_fix_co_filename(PyObject *self, PyObject *args)
{
    PyObject *co;
    PyObject *file_path;

    if (!PyArg_ParseTuple(args, "OO:_fix_co_filename", &co, &file_path))
        return NULL;

    if (!PyCode_Check(co)) {
        PyErr_SetString(PyExc_TypeError,
                        "first argument must be a code object");
        return NULL;
    }

    if (!PyUnicode_Check(file_path)) {
        PyErr_SetString(PyExc_TypeError,
                        "second argument must be a string");
        return NULL;
    }

    update_compiled_module((PyCodeObject*)co, file_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, cmp;
    for (i = 0; PyImport_Inittab[i].name != NULL; i++) {
        cmp = PyUnicode_CompareWithASCIIString(name, PyImport_Inittab[i].name);
        if (cmp == 0) {
            if (PyImport_Inittab[i].initfunc == NULL)
                return -1;
            else
                return 1;
        }
    }
    return 0;
}


/* Return an importer 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 it should fall back to the builtin
   import mechanism. Cache the result in path_importer_cache.
   Returns a borrowed reference. */

static PyObject *
get_path_importer(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_GetItem(path_importer_cache, p);
    if (importer != NULL)
        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_CallFunctionObjArgs(hook, p, NULL);
        if (importer != NULL)
            break;

        if (!PyErr_ExceptionMatches(PyExc_ImportError)) {
            return NULL;
        }
        PyErr_Clear();
    }
    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;
}

PyAPI_FUNC(PyObject *)
PyImport_GetImporter(PyObject *path) {
    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(path_importer_cache,
                                     path_hooks, path);
    }
    Py_XINCREF(importer); /* get_path_importer returns a borrowed reference */
    return importer;
}


static int init_builtin(PyObject *); /* Forward */

/* Initialize a built-in module.
   Return 1 for success, 0 if the module is not found, and -1 with
   an exception set if the initialization failed. */

static int
init_builtin(PyObject *name)
{
    struct _inittab *p;

    if (_PyImport_FindExtensionObject(name, name) != NULL)
        return 1;

    for (p = PyImport_Inittab; p->name != NULL; p++) {
        PyObject *mod;
        PyModuleDef *def;
        if (PyUnicode_CompareWithASCIIString(name, p->name) == 0) {
            if (p->initfunc == NULL) {
                PyErr_Format(PyExc_ImportError,
                    "Cannot re-init internal module %R",
                    name);
                return -1;
            }
            mod = (*p->initfunc)();
            if (mod == 0)
                return -1;
            /* Remember pointer to module init function. */
            def = PyModule_GetDef(mod);
            def->m_base.m_init = p->initfunc;
            if (_PyImport_FixupExtensionObject(mod, name, name) < 0)
                return -1;
            /* FixupExtension has put the module into sys.modules,
               so we can release our own reference. */
            Py_DECREF(mod);
            return 1;
        }
    }
    return 0;
}


/* 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_CompareWithASCIIString(name, p->name) == 0)
            break;
    }
    return p;
}