Python/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

#ifdef MS_WINDOWS
/* for stat.st_mode */
typedef unsigned short mode_t;
/* for _mkdir */
#include <direct.h>
#endif


#define CACHEDIR "__pycache__"

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

/* Function from Parser/tokenizer.c */
extern char * PyTokenizer_FindEncodingFilename(int, PyObject *);

/* 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)
        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();
        PyThread_acquire_lock(import_lock, 0);
        /* XXX: can the previous line fail? */
        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",
    /* 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, ndone;
    PyObject *key, *value, *dict;
    PyInterpreterState *interp = PyThreadState_GET()->interp;
    PyObject *modules = interp->modules;

    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. */

    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);
        }
    }

    /* First, delete __main__ */
    value = PyDict_GetItemString(modules, "__main__");
    if (value != NULL && PyModule_Check(value)) {
        if (Py_VerboseFlag)
            PySys_WriteStderr("# cleanup __main__\n");
        _PyModule_Clear(value);
        PyDict_SetItemString(modules, "__main__", Py_None);
    }

    /* 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).

       Also note that we 'delete' modules by replacing their entry
       in the modules dict with None, rather than really deleting
       them; this avoids a rehash of the modules dictionary and
       also marks them as "non existent" so they won't be
       re-imported. */

    /* Next, repeatedly delete modules with a reference count of
       one (skipping builtins and sys) and delete them */
    do {
        ndone = 0;
        pos = 0;
        while (PyDict_Next(modules, &pos, &key, &value)) {
            if (value->ob_refcnt != 1)
                continue;
            if (PyUnicode_Check(key) && PyModule_Check(value)) {
                if (PyUnicode_CompareWithASCIIString(key, "builtins") == 0)
                    continue;
                if (PyUnicode_CompareWithASCIIString(key, "sys") == 0)
                    continue;
                if (Py_VerboseFlag)
                    PySys_FormatStderr(
                        "# cleanup[1] %U\n", key);
                _PyModule_Clear(value);
                PyDict_SetItem(modules, key, Py_None);
                ndone++;
            }
        }
    } while (ndone > 0);

    /* Next, delete all modules (still skipping builtins and sys) */
    pos = 0;
    while (PyDict_Next(modules, &pos, &key, &value)) {
        if (PyUnicode_Check(key) && PyModule_Check(value)) {
            if (PyUnicode_CompareWithASCIIString(key, "builtins") == 0)
                continue;
            if (PyUnicode_CompareWithASCIIString(key, "sys") == 0)
                continue;
            if (Py_VerboseFlag)
                PySys_FormatStderr("# cleanup[2] %U\n", key);
            _PyModule_Clear(value);
            PyDict_SetItem(modules, key, Py_None);
        }
    }

    /* Next, delete sys and builtins (in that order) */
    value = PyDict_GetItemString(modules, "sys");
    if (value != NULL && PyModule_Check(value)) {
        if (Py_VerboseFlag)
            PySys_WriteStderr("# cleanup sys\n");
        _PyModule_Clear(value);
        PyDict_SetItemString(modules, "sys", Py_None);
    }
    value = PyDict_GetItemString(modules, "builtins");
    if (value != NULL && PyModule_Check(value)) {
        if (Py_VerboseFlag)
            PySys_WriteStderr("# cleanup builtins\n");
        _PyModule_Clear(value);
        PyDict_SetItemString(modules, "builtins", Py_None);
    }

    /* Finally, clear and delete the modules directory */
    PyDict_Clear(modules);
    interp->modules = NULL;
    Py_DECREF(modules);
}


/* 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 module name
   (for built-in modules) or by filename (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;
    struct PyModuleDef *def;
    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;
    }
    PyDict_SetItem(extensions, filename, (PyObject*)def);
    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;
    PyModuleDef* def;
    if (extensions == NULL)
        return NULL;
    def = (PyModuleDef*)PyDict_GetItem(extensions, filename);
    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_CallMethodObjIdArgs(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 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;

    if ((path_importer_cache = PySys_GetObject("path_importer_cache"))) {
        if ((path_hooks = PySys_GetObject("path_hooks"))) {
            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 struct _frozen *
find_frozen(PyObject *name)
{
    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;
}

static PyObject *
get_frozen_object(PyObject *name)
{
    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((char *)p->code, size);
}

static PyObject *
is_frozen_package(PyObject *name)
{
    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)
{
    struct _frozen *p;
    PyObject *co, *m, *path;
    int ispackage;
    int size;

    p = find_frozen(name);

    if (p == NULL)
        return 0;
    if (p->code == NULL) {
        PyErr_Format(PyExc_ImportError,
                     "Excluded frozen object named %R",
                     name);
        return -1;
    }
    size = p->size;
    ispackage = (size < 0);
    if (ispackage)
        size = -size;
    co = PyMarshal_ReadObjectFromString((char *)p->code, size);
    if (co == NULL)
        return -1;
    if (!PyCode_Check(co)) {
        PyErr_Format(PyExc_TypeError,
                     "frozen object %R is not a code object",
                     name);
        goto err_return;
    }
    if (ispackage) {
        /* Set __path__ to the package name */
        PyObject *d, *l;
        int err;
        m = PyImport_AddModuleObject(name);
        if (m == NULL)
            goto err_return;
        d = PyModule_GetDict(m);
        l = PyList_New(1);
        if (l == NULL) {
            goto err_return;
        }
        Py_INCREF(name);
        PyList_SET_ITEM(l, 0, name);
        err = PyDict_SetItemString(d, "__path__", l);
        Py_DECREF(l);
        if (err != 0)
            goto err_return;
    }
    path = PyUnicode_FromString("<frozen>");
    if (path == NULL)
        goto err_return;
    m = PyImport_ExecCodeModuleObject(name, co, path, NULL);
    Py_DECREF(path);
    if (m == NULL)
        goto err_return;
    Py_DECREF(co);
    Py_DECREF(m);
    return 1;
err_return:
    Py_DECREF(co);
    return -1;
}

int
PyImport_ImportFrozenModule(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(void)
{
    const char *importlib_filename = "<frozen importlib._bootstrap>";
    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(&exception, &value, &base_tb);
    if (!exception || Py_VerboseFlag)
        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 = frame->f_code;
        int now_in_importlib;

        assert(PyTraceBack_Check(tb));
        now_in_importlib = (PyUnicode_CompareWithASCIIString(
                                code->co_filename,
                                importlib_filename) == 0);
        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_CompareWithASCIIString(code->co_name,
                                              remove_frames) == 0)) {
            PyObject *tmp = *outer_link;
            *outer_link = next;
            Py_XINCREF(next);
            Py_DECREF(tmp);
            prev_link = outer_link;
        }
        else {
            prev_link = (PyObject **) &traceback->tb_next;
        }
        tb = next;
    }
done:
    PyErr_Restore(exception, value, base_tb);
}


PyObject *
PyImport_ImportModuleLevelObject(PyObject *name, PyObject *given_globals,
                                 PyObject *locals, PyObject *given_fromlist,
                                 int level)
{
    _Py_IDENTIFIER(__import__);
    _Py_IDENTIFIER(__initializing__);
    _Py_IDENTIFIER(__package__);
    _Py_IDENTIFIER(__path__);
    _Py_IDENTIFIER(__name__);
    _Py_IDENTIFIER(_find_and_load);
    _Py_IDENTIFIER(_handle_fromlist);
    _Py_IDENTIFIER(_lock_unlock_module);
    _Py_static_string(single_dot, ".");
    PyObject *abs_name = NULL;
    PyObject *builtins_import = NULL;
    PyObject *final_mod = NULL;
    PyObject *mod = NULL;
    PyObject *package = NULL;
    PyObject *globals = NULL;
    PyObject *fromlist = NULL;
    PyInterpreterState *interp = PyThreadState_GET()->interp;

    /* Make sure to use default values so as to not have
       PyObject_CallMethodObjArgs() truncate the parameter list because of a
       NULL argument. */
    if (given_globals == NULL) {
        globals = PyDict_New();
        if (globals == NULL) {
            goto error;
        }
    }
    else {
        /* Only have to care what given_globals is if it will be used
           for something. */
        if (level > 0 && !PyDict_Check(given_globals)) {
            PyErr_SetString(PyExc_TypeError, "globals must be a dict");
            goto error;
        }
        globals = given_globals;
        Py_INCREF(globals);
    }

    if (given_fromlist == NULL) {
        fromlist = PyList_New(0);
        if (fromlist == NULL) {
            goto error;
        }
    }
    else {
        fromlist = given_fromlist;
        Py_INCREF(fromlist);
    }
    if (name == NULL) {
        PyErr_SetString(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(PyExc_TypeError, "module name must be a string");
        goto error;
    }
    else if (PyUnicode_READY(name) < 0) {
        goto error;
    }
    if (level < 0) {
        PyErr_SetString(PyExc_ValueError, "level must be >= 0");
        goto error;
    }
    else if (level > 0) {
        package = _PyDict_GetItemId(globals, &PyId___package__);
        if (package != NULL && package != Py_None) {
            Py_INCREF(package);
            if (!PyUnicode_Check(package)) {
                PyErr_SetString(PyExc_TypeError, "package must be a string");
                goto error;
            }
        }
        else {
            package = _PyDict_GetItemId(globals, &PyId___name__);
            if (package == NULL) {
                PyErr_SetString(PyExc_KeyError, "'__name__' not in globals");
                goto error;
            }
            else if (!PyUnicode_Check(package)) {
                PyErr_SetString(PyExc_TypeError, "__name__ must be a string");
            }
            Py_INCREF(package);

            if (_PyDict_GetItemId(globals, &PyId___path__) == NULL) {
                PyObject *partition = NULL;
                PyObject *borrowed_dot = _PyUnicode_FromId(&single_dot);
                if (borrowed_dot == NULL) {
                    goto error;
                }
                partition = PyUnicode_RPartition(package, borrowed_dot);
                Py_DECREF(package);
                if (partition == NULL) {
                    goto error;
                }
                package = PyTuple_GET_ITEM(partition, 0);
                Py_INCREF(package);
                Py_DECREF(partition);
            }
        }

        if (PyDict_GetItem(interp->modules, package) == NULL) {
            PyErr_Format(PyExc_SystemError,
                    "Parent module %R not loaded, cannot perform relative "
                    "import", package);
            goto error;
        }
    }
    else {  /* level == 0 */
        if (PyUnicode_GET_LENGTH(name) == 0) {
            PyErr_SetString(PyExc_ValueError, "Empty module name");
            goto error;
        }
        package = Py_None;
        Py_INCREF(package);
    }

    if (level > 0) {
        Py_ssize_t last_dot = PyUnicode_GET_LENGTH(package);
        PyObject *base = NULL;
        int level_up = 1;

        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(PyExc_ValueError,
                                "attempted relative import beyond top-level "
                                "package");
                goto error;
            }
        }
        base = PyUnicode_Substring(package, 0, last_dot);
        if (PyUnicode_GET_LENGTH(name) > 0) {
            PyObject *borrowed_dot, *seq = NULL;

            borrowed_dot = _PyUnicode_FromId(&single_dot);
            seq = PyTuple_Pack(2, base, name);
            Py_DECREF(base);
            if (borrowed_dot == NULL || seq == NULL) {
                goto error;
            }

            abs_name = PyUnicode_Join(borrowed_dot, seq);
            Py_DECREF(seq);
            if (abs_name == NULL) {
                goto error;
            }
        }
        else {
            abs_name = base;
        }
    }
    else {
        abs_name = name;
        Py_INCREF(abs_name);
    }

#ifdef WITH_THREAD
    _PyImport_AcquireLock();
#endif
   /* From this point forward, goto error_with_unlock! */
    if (PyDict_Check(globals)) {
        builtins_import = _PyDict_GetItemId(globals, &PyId___import__);
    }
    if (builtins_import == NULL) {
        builtins_import = _PyDict_GetItemId(interp->builtins, &PyId___import__);
        if (builtins_import == NULL) {
            PyErr_SetString(PyExc_ImportError, "__import__ not found");
            goto error_with_unlock;
        }
    }
    Py_INCREF(builtins_import);

    mod = PyDict_GetItem(interp->modules, abs_name);
    if (mod == Py_None) {
        PyObject *msg = PyUnicode_FromFormat("import of %R halted; "
                                             "None in sys.modules", abs_name);
        if (msg != NULL) {
            PyErr_SetImportError(msg, abs_name, NULL);
            Py_DECREF(msg);
        }
        mod = NULL;
        goto error_with_unlock;
    }
    else if (mod != NULL) {
        PyObject *value;
        int initializing = 0;

        Py_INCREF(mod);
        /* Optimization: only call _bootstrap._lock_unlock_module() if
           __initializing__ is true.
           NOTE: because of this, __initializing__ must be set *before*
           stuffing the new module in sys.modules.
         */
        value = _PyObject_GetAttrId(mod, &PyId___initializing__);
        if (value == NULL)
            PyErr_Clear();
        else {
            initializing = PyObject_IsTrue(value);
            Py_DECREF(value);
            if (initializing == -1)
                PyErr_Clear();
        }
        if (initializing > 0) {
            /* _bootstrap._lock_unlock_module() releases the import lock */
            value = _PyObject_CallMethodObjIdArgs(interp->importlib,
                                            &PyId__lock_unlock_module, abs_name,
                                            NULL);
            if (value == NULL)
                goto error;
            Py_DECREF(value);
        }
        else {
#ifdef WITH_THREAD
            if (_PyImport_ReleaseLock() < 0) {
                PyErr_SetString(PyExc_RuntimeError, "not holding the import lock");
                goto error;
            }
#endif
        }
    }
    else {
        /* _bootstrap._find_and_load() releases the import lock */
        mod = _PyObject_CallMethodObjIdArgs(interp->importlib,
                                            &PyId__find_and_load, abs_name,
                                            builtins_import, NULL);
        if (mod == NULL) {
            goto error;
        }
    }
    /* From now on we don't hold the import lock anymore. */

    if (PyObject_Not(fromlist)) {
        if (level == 0 || PyUnicode_GET_LENGTH(name) > 0) {
            PyObject *front = NULL;
            PyObject *partition = NULL;
            PyObject *borrowed_dot = _PyUnicode_FromId(&single_dot);

            if (borrowed_dot == NULL) {
                goto error;
            }

            partition = PyUnicode_Partition(name, borrowed_dot);
            if (partition == NULL) {
                goto error;
            }

            if (PyUnicode_GET_LENGTH(PyTuple_GET_ITEM(partition, 1)) == 0) {
                /* No dot in module name, simple exit */
                Py_DECREF(partition);
                final_mod = mod;
                Py_INCREF(mod);
                goto error;
            }

            front = PyTuple_GET_ITEM(partition, 0);
            Py_INCREF(front);
            Py_DECREF(partition);

            if (level == 0) {
                final_mod = PyObject_CallFunctionObjArgs(builtins_import, front, NULL);
                Py_DECREF(front);
            }
            else {
                Py_ssize_t cut_off = PyUnicode_GET_LENGTH(name) -
                                        PyUnicode_GET_LENGTH(front);
                Py_ssize_t abs_name_len = PyUnicode_GET_LENGTH(abs_name);
                PyObject *to_return = PyUnicode_Substring(abs_name, 0,
                                                        abs_name_len - cut_off);
                Py_DECREF(front);
                if (to_return == NULL) {
                    goto error;
                }

                final_mod = PyDict_GetItem(interp->modules, to_return);
                if (final_mod == NULL) {
                    PyErr_Format(PyExc_KeyError,
                                 "%R not in sys.modules as expected",
                                 to_return);
                }
                else {
                    Py_INCREF(final_mod);
                }
                Py_DECREF(to_return);
            }
        }
        else {
            final_mod = mod;
            Py_INCREF(mod);
        }
    }
    else {
        final_mod = _PyObject_CallMethodObjIdArgs(interp->importlib,
                                                  &PyId__handle_fromlist, mod,
                                                  fromlist, builtins_import,
                                                  NULL);
    }
    goto error;

  error_with_unlock:
#ifdef WITH_THREAD
    if (_PyImport_ReleaseLock() < 0) {
        PyErr_SetString(PyExc_RuntimeError, "not holding the import lock");
    }
#endif
  error:
    Py_XDECREF(abs_name);
    Py_XDECREF(builtins_import);
    Py_XDECREF(mod);
    Py_XDECREF(package);
    Py_XDECREF(globals);
    Py_XDECREF(fromlist);
    if (final_mod == NULL)
        remove_importlib_frames();
    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(reload);
    PyObject *reloaded_module = NULL;
    PyObject *modules = PyImport_GetModuleDict();
    PyObject *imp = PyDict_GetItemString(modules, "imp");
    if (imp == NULL) {
        imp = PyImport_ImportModule("imp");
        if (imp == NULL) {
            return NULL;
        }
    }
    else {
        Py_INCREF(imp);
    }

    reloaded_module = _PyObject_CallMethodId(imp, &PyId_reload, "O", m);
    Py_DECREF(imp);
    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)
{
    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 *modules = 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(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);

    modules = PyImport_GetModuleDict();
    r = PyDict_GetItem(modules, module_name);
    if (r != NULL)
        Py_INCREF(r);

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

    return r;
}

static PyObject *
imp_extension_suffixes(PyObject *self, PyObject *noargs)
{
    PyObject *list;
    const char *suffix;
    unsigned int index = 0;

    list = PyList_New(0);
    if (list == NULL)
        return NULL;
#ifdef HAVE_DYNAMIC_LOADING
    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;
}

static PyObject *
imp_init_builtin(PyObject *self, PyObject *args)
{
    PyObject *name;
    int ret;
    PyObject *m;
    if (!PyArg_ParseTuple(args, "U:init_builtin", &name))
        return NULL;
    ret = init_builtin(name);
    if (ret < 0)
        return NULL;
    if (ret == 0) {
        Py_INCREF(Py_None);
        return Py_None;
    }
    m = PyImport_AddModuleObject(name);
    Py_XINCREF(m);
    return m;
}

static PyObject *
imp_init_frozen(PyObject *self, PyObject *args)
{
    PyObject *name;
    int ret;
    PyObject *m;
    if (!PyArg_ParseTuple(args, "U:init_frozen", &name))
        return NULL;
    ret = PyImport_ImportFrozenModuleObject(name);
    if (ret < 0)
        return NULL;
    if (ret == 0) {
        Py_INCREF(Py_None);
        return Py_None;
    }
    m = PyImport_AddModuleObject(name);
    Py_XINCREF(m);
    return m;
}

static PyObject *
imp_get_frozen_object(PyObject *self, PyObject *args)
{
    PyObject *name;

    if (!PyArg_ParseTuple(args, "U:get_frozen_object", &name))
        return NULL;
    return get_frozen_object(name);
}

static PyObject *
imp_is_frozen_package(PyObject *self, PyObject *args)
{
    PyObject *name;

    if (!PyArg_ParseTuple(args, "U:is_frozen_package", &name))
        return NULL;
    return is_frozen_package(name);
}

static PyObject *
imp_is_builtin(PyObject *self, PyObject *args)
{
    PyObject *name;
    if (!PyArg_ParseTuple(args, "U:is_builtin", &name))
        return NULL;
    return PyLong_FromLong(is_builtin(name));
}

static PyObject *
imp_is_frozen(PyObject *self, PyObject *args)
{
    PyObject *name;
    struct _frozen *p;
    if (!PyArg_ParseTuple(args, "U:is_frozen", &name))
        return NULL;
    p = find_frozen(name);
    return PyBool_FromLong((long) (p == NULL ? 0 : p->size));
}

#ifdef HAVE_DYNAMIC_LOADING

static PyObject *
imp_load_dynamic(PyObject *self, PyObject *args)
{
    PyObject *name, *pathname, *fob = NULL, *mod;
    FILE *fp;

    if (!PyArg_ParseTuple(args, "UO&|O:load_dynamic",
                          &name, PyUnicode_FSDecoder, &pathname, &fob))
        return NULL;
    if (fob != NULL) {
        fp = _Py_fopen(pathname, "r");
        if (fp == NULL) {
            Py_DECREF(pathname);
            if (!PyErr_Occurred())
                PyErr_SetFromErrno(PyExc_IOError);
            return NULL;
        }
    }
    else
        fp = NULL;
    mod = _PyImport_LoadDynamicModule(name, pathname, fp);
    Py_DECREF(pathname);
    if (fp)
        fclose(fp);
    return mod;
}

#endif /* HAVE_DYNAMIC_LOADING */


/* Doc strings */

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

PyDoc_STRVAR(doc_extension_suffixes,
"extension_suffixes() -> list of strings\n\
Returns the list of file suffixes used to identify extension modules.");

PyDoc_STRVAR(doc_lock_held,
"lock_held() -> boolean\n\
Return True if the import lock is currently held, else False.\n\
On platforms without threads, return False.");

PyDoc_STRVAR(doc_acquire_lock,
"acquire_lock() -> None\n\
Acquires the interpreter's import lock for the current thread.\n\
This lock should be used by import hooks to ensure thread-safety\n\
when importing modules.\n\
On platforms without threads, this function does nothing.");

PyDoc_STRVAR(doc_release_lock,
"release_lock() -> None\n\
Release the interpreter's import lock.\n\
On platforms without threads, this function does nothing.");

static PyMethodDef imp_methods[] = {
    {"extension_suffixes", imp_extension_suffixes, METH_NOARGS,
        doc_extension_suffixes},
    {"lock_held",        imp_lock_held,    METH_NOARGS,  doc_lock_held},
    {"acquire_lock", imp_acquire_lock, METH_NOARGS,  doc_acquire_lock},
    {"release_lock", imp_release_lock, METH_NOARGS,  doc_release_lock},
    {"get_frozen_object",       imp_get_frozen_object,  METH_VARARGS},
    {"is_frozen_package",   imp_is_frozen_package,  METH_VARARGS},
    {"init_builtin",            imp_init_builtin,       METH_VARARGS},
    {"init_frozen",             imp_init_frozen,        METH_VARARGS},
    {"is_builtin",              imp_is_builtin,         METH_VARARGS},
    {"is_frozen",               imp_is_frozen,          METH_VARARGS},
#ifdef HAVE_DYNAMIC_LOADING
    {"load_dynamic",            imp_load_dynamic,       METH_VARARGS},
#endif
    {"_fix_co_filename",        imp_fix_co_filename,    METH_VARARGS},
    {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;

    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)
{
    static struct _inittab *our_copy = NULL;
    struct _inittab *p;
    int i, n;

    /* 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++)
        ;

    /* Allocate new memory for the combined table */
    p = our_copy;
    PyMem_RESIZE(p, struct _inittab, i+n+1);
    if (p == NULL)
        return -1;

    /* Copy the tables into the new memory */
    if (our_copy != PyImport_Inittab)
        memcpy(p, PyImport_Inittab, (i+1) * sizeof(struct _inittab));
    PyImport_Inittab = our_copy = p;
    memcpy(p+i, newtab, (n+1) * sizeof(struct _inittab));

    return 0;
}

/* 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 = (char *)name;
    newtab[0].initfunc = initfunc;

    return PyImport_ExtendInittab(newtab);
}

#ifdef __cplusplus
}
#endif