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 "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


/* Magic word to reject .pyc files generated by other Python versions.
   It should change for each incompatible change to the bytecode.

   The value of CR and LF is incorporated so if you ever read or write
   a .pyc file in text mode the magic number will be wrong; also, the
   Apple MPW compiler swaps their values, botching string constants.

   The magic numbers must be spaced apart at least 2 values, as the
   -U interpeter flag will cause MAGIC+1 being used. They have been
   odd numbers for some time now.

   There were a variety of old schemes for setting the magic number.
   The current working scheme is to increment the previous value by
   10.

   Starting with the adoption of PEP 3147 in Python 3.2, every bump in magic
   number also includes a new "magic tag", i.e. a human readable string used
   to represent the magic number in __pycache__ directories.  When you change
   the magic number, you must also set a new unique magic tag.  Generally this
   can be named after the Python major version of the magic number bump, but
   it can really be anything, as long as it's different than anything else
   that's come before.  The tags are included in the following table, starting
   with Python 3.2a0.

   Known values:
       Python 1.5:   20121
       Python 1.5.1: 20121
       Python 1.5.2: 20121
       Python 1.6:   50428
       Python 2.0:   50823
       Python 2.0.1: 50823
       Python 2.1:   60202
       Python 2.1.1: 60202
       Python 2.1.2: 60202
       Python 2.2:   60717
       Python 2.3a0: 62011
       Python 2.3a0: 62021
       Python 2.3a0: 62011 (!)
       Python 2.4a0: 62041
       Python 2.4a3: 62051
       Python 2.4b1: 62061
       Python 2.5a0: 62071
       Python 2.5a0: 62081 (ast-branch)
       Python 2.5a0: 62091 (with)
       Python 2.5a0: 62092 (changed WITH_CLEANUP opcode)
       Python 2.5b3: 62101 (fix wrong code: for x, in ...)
       Python 2.5b3: 62111 (fix wrong code: x += yield)
       Python 2.5c1: 62121 (fix wrong lnotab with for loops and
                            storing constants that should have been removed)
       Python 2.5c2: 62131 (fix wrong code: for x, in ... in listcomp/genexp)
       Python 2.6a0: 62151 (peephole optimizations and STORE_MAP opcode)
       Python 2.6a1: 62161 (WITH_CLEANUP optimization)
       Python 3000:   3000
                      3010 (removed UNARY_CONVERT)
                      3020 (added BUILD_SET)
                      3030 (added keyword-only parameters)
                      3040 (added signature annotations)
                      3050 (print becomes a function)
                      3060 (PEP 3115 metaclass syntax)
                      3061 (string literals become unicode)
                      3071 (PEP 3109 raise changes)
                      3081 (PEP 3137 make __file__ and __name__ unicode)
                      3091 (kill str8 interning)
                      3101 (merge from 2.6a0, see 62151)
                      3103 (__file__ points to source file)
       Python 3.0a4: 3111 (WITH_CLEANUP optimization).
       Python 3.0a5: 3131 (lexical exception stacking, including POP_EXCEPT)
       Python 3.1a0: 3141 (optimize list, set and dict comprehensions:
               change LIST_APPEND and SET_ADD, add MAP_ADD)
       Python 3.1a0: 3151 (optimize conditional branches:
               introduce POP_JUMP_IF_FALSE and POP_JUMP_IF_TRUE)
       Python 3.2a0: 3160 (add SETUP_WITH)
                     tag: cpython-32
       Python 3.2a1: 3170 (add DUP_TOP_TWO, remove DUP_TOPX and ROT_FOUR)
                     tag: cpython-32
       Python 3.2a2  3180 (add DELETE_DEREF)
       Python 3.3a0  3190 __class__ super closure changed
*/

/* MAGIC must change whenever the bytecode emitted by the compiler may no
   longer be understood by older implementations of the eval loop (usually
   due to the addition of new opcodes)
   TAG and PYC_TAG_UNICODE must change for each major Python release. The magic
   number will take care of any bytecode changes that occur during development.
*/
#define QUOTE(arg) #arg
#define STRIFY(name) QUOTE(name)
#define MAJOR STRIFY(PY_MAJOR_VERSION)
#define MINOR STRIFY(PY_MINOR_VERSION)
#define MAGIC (3190 | ((long)'\r'<<16) | ((long)'\n'<<24))
#define TAG "cpython-" MAJOR MINOR;
#define CACHEDIR "__pycache__"
static const Py_UCS4 CACHEDIR_UNICODE[] = {
    '_', '_', 'p', 'y', 'c', 'a', 'c', 'h', 'e', '_', '_', '\0'};
/* Current magic word and string tag as globals. */
static long pyc_magic = MAGIC;
static const char *pyc_tag = TAG;
static const Py_UCS4 PYC_TAG_UNICODE[] = {
    'c', 'p', 'y', 't', 'h', 'o', 'n', '-', PY_MAJOR_VERSION + 48, PY_MINOR_VERSION + 48, '\0'};
#undef QUOTE
#undef STRIFY
#undef MAJOR
#undef MINOR

/* 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;

/* these tables define the module suffixes that Python recognizes */
struct filedescr * _PyImport_Filetab = NULL;

static const struct filedescr _PyImport_StandardFiletab[] = {
    {".py", "U", PY_SOURCE},
#ifdef MS_WINDOWS
    {".pyw", "U", PY_SOURCE},
#endif
    {".pyc", "rb", PY_COMPILED},
    {0, 0}
};

static PyObject *initstr = NULL;


/* Initialize things */

void
_PyImport_Init(void)
{
    const struct filedescr *scan;
    struct filedescr *filetab;
    int countD = 0;
    int countS = 0;

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

    /* prepare _PyImport_Filetab: copy entries from
       _PyImport_DynLoadFiletab and _PyImport_StandardFiletab.
     */
#ifdef HAVE_DYNAMIC_LOADING
    for (scan = _PyImport_DynLoadFiletab; scan->suffix != NULL; ++scan)
        ++countD;
#endif
    for (scan = _PyImport_StandardFiletab; scan->suffix != NULL; ++scan)
        ++countS;
    filetab = PyMem_NEW(struct filedescr, countD + countS + 1);
    if (filetab == NULL)
        Py_FatalError("Can't initialize import file table.");
#ifdef HAVE_DYNAMIC_LOADING
    memcpy(filetab, _PyImport_DynLoadFiletab,
           countD * sizeof(struct filedescr));
#endif
    memcpy(filetab + countD, _PyImport_StandardFiletab,
           countS * sizeof(struct filedescr));
    filetab[countD + countS].suffix = NULL;

    _PyImport_Filetab = filetab;

    if (Py_OptimizeFlag) {
        /* Replace ".pyc" with ".pyo" in _PyImport_Filetab */
        for (; filetab->suffix != NULL; filetab++) {
            if (strcmp(filetab->suffix, ".pyc") == 0)
                filetab->suffix = ".pyo";
        }
    }
}

void
_PyImportHooks_Init(void)
{
    PyObject *v, *path_hooks = NULL, *zimpimport;
    int err = 0;

    /* adding sys.path_hooks and sys.path_importer_cache, setting up
       zipimport */
    if (PyType_Ready(&PyNullImporter_Type) < 0)
        goto error;

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

    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, "
                      "path_importer_cache, or NullImporter failed"
                      );
    }

    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 {
        PyObject *zipimporter = PyObject_GetAttrString(zimpimport,
                                                       "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.append(zipimporter) */
            err = PyList_Append(path_hooks, zipimporter);
            Py_DECREF(zipimporter);
            if (err)
                goto error;
            if (Py_VerboseFlag)
                PySys_WriteStderr(
                    "# installed zipimport hook\n");
        }
    }
    Py_DECREF(path_hooks);
}

void
_PyImport_Fini(void)
{
    Py_XDECREF(extensions);
    extensions = NULL;
    PyMem_DEL(_PyImport_Filetab);
    _PyImport_Filetab = NULL;
}


/* 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);
    }
    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--;
    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;
}

static void
imp_modules_reloading_clear(void)
{
    PyInterpreterState *interp = PyThreadState_Get()->interp;
    if (interp->modules_reloading != NULL)
        PyDict_Clear(interp->modules_reloading);
}

/* 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);
    Py_CLEAR(interp->modules_reloading);
}


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

long
PyImport_GetMagicNumber(void)
{
    return pyc_magic;
}


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

/* 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;
        PyDict_SetItem(PyImport_GetModuleDict(), name, mod);
        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");
}

static PyObject * get_sourcefile(PyObject *filename);
static PyObject *make_source_pathname(PyObject *pathname);
static PyObject* make_compiled_pathname(PyObject *pathname, int debug);

/* 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 (pathname != NULL) {
        pathobj = PyUnicode_DecodeFSDefault(pathname);
        if (pathobj == NULL)
            goto error;
    } else
        pathobj = NULL;
    if (cpathname != NULL) {
        cpathobj = PyUnicode_DecodeFSDefault(cpathname);
        if (cpathobj == NULL)
            goto error;
    } else
        cpathobj = 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;
    }
    /* Remember the filename as the __file__ attribute */
    if (pathname != NULL) {
        v = get_sourcefile(pathname);
        if (v == NULL)
            PyErr_Clear();
    }
    else
        v = NULL;
    if (v == NULL) {
        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;
}


/* Like strrchr(string, '/') but searches for the rightmost of either SEP
   or ALTSEP, if the latter is defined.
*/
static Py_UCS4*
rightmost_sep(Py_UCS4 *s)
{
    Py_UCS4 *found, c;
    for (found = NULL; (c = *s); s++) {
        if (c == SEP
#ifdef ALTSEP
            || c == ALTSEP
#endif
            )
        {
            found = s;
        }
    }
    return found;
}


/* Given a pathname for a Python source file, fill a buffer with the
   pathname for the corresponding compiled file.  Return the pathname
   for the compiled file, or NULL if there's no space in the buffer.
   Doesn't set an exception.

   foo.py -> __pycache__/foo.<tag>.pyc */

static PyObject*
make_compiled_pathname(PyObject *pathstr, int debug)
{
    Py_UCS4 *pathname;
    Py_UCS4 buf[MAXPATHLEN];
    size_t buflen = (size_t)MAXPATHLEN;
    size_t len;
    size_t i, save;
    Py_UCS4 *pos;
    int sep = SEP;

    pathname = PyUnicode_AsUCS4Copy(pathstr);
    if (!pathname)
        return NULL;
    len = Py_UCS4_strlen(pathname);

    /* Sanity check that the buffer has roughly enough space to hold what
       will eventually be the full path to the compiled file.  The 5 extra
       bytes include the slash afer __pycache__, the two extra dots, the
       extra trailing character ('c' or 'o') and null.  This isn't exact
       because the contents of the buffer can affect how many actual
       characters of the string get into the buffer.  We'll do a final
       sanity check before writing the extension to ensure we do not
       overflow the buffer.
    */
    if (len + Py_UCS4_strlen(CACHEDIR_UNICODE) + Py_UCS4_strlen(PYC_TAG_UNICODE) + 5 > buflen) {
        PyMem_Free(pathname);
        return NULL;
    }

    /* Find the last path separator and copy everything from the start of
       the source string up to and including the separator.
    */
    pos = rightmost_sep(pathname);
    if (pos == NULL) {
        i = 0;
    }
    else {
        sep = *pos;
        i = pos - pathname + 1;
        Py_UCS4_strncpy(buf, pathname, i);
    }

    save = i;
    buf[i++] = '\0';
    /* Add __pycache__/ */
    Py_UCS4_strcat(buf, CACHEDIR_UNICODE);
    i += Py_UCS4_strlen(CACHEDIR_UNICODE) - 1;
    buf[i++] = sep;
    buf[i] = '\0';
    /* Add the base filename, but remove the .py or .pyw extension, since
       the tag name must go before the extension.
    */
    Py_UCS4_strcat(buf, pathname + save);
    pos = Py_UCS4_strrchr(buf + i, '.');
    if (pos != NULL)
        *++pos = '\0';

    /* pathname is not used from here on. */
    PyMem_Free(pathname);

    Py_UCS4_strcat(buf, PYC_TAG_UNICODE);
    /* The length test above assumes that we're only adding one character
       to the end of what would normally be the extension.  What if there
       is no extension, or the string ends in '.' or '.p', and otherwise
       fills the buffer?  By appending 4 more characters onto the string
       here, we could overrun the buffer.

       As a simple example, let's say buflen=32 and the input string is
       'xxx.py'.  strlen() would be 6 and the test above would yield:

       (6 + 11 + 10 + 5 == 32) > 32

       which is false and so the name mangling would continue.  This would
       be fine because we'd end up with this string in buf:

       __pycache__/xxx.cpython-32.pyc\0

       strlen(of that) == 30 + the nul fits inside a 32 character buffer.
       We can even handle an input string of say 'xxxxx' above because
       that's (5 + 11 + 10 + 5 == 31) > 32 which is also false.  Name
       mangling that yields:

       __pycache__/xxxxxcpython-32.pyc\0

       which is 32 characters including the nul, and thus fits in the
       buffer. However, an input string of 'xxxxxx' would yield a result
       string of:

       __pycache__/xxxxxxcpython-32.pyc\0

       which is 33 characters long (including the nul), thus overflowing
       the buffer, even though the first test would fail, i.e.: the input
       string is also 6 characters long, so 32 > 32 is false.

       The reason the first test fails but we still overflow the buffer is
       that the test above only expects to add one extra character to be
       added to the extension, and here we're adding three (pyc).  We
       don't add the first dot, so that reclaims one of expected
       positions, leaving us overflowing by 1 byte (3 extra - 1 reclaimed
       dot - 1 expected extra == 1 overflowed).

       The best we can do is ensure that we still have enough room in the
       target buffer before we write the extension.  Because it's always
       only the extension that can cause the overflow, and never the other
       path bytes we've written, it's sufficient to just do one more test
       here.  Still, the assertion that follows can't hurt.
    */
#if 0
    printf("strlen(buf): %d; buflen: %d\n", (int)strlen(buf), (int)buflen);
#endif
    len = Py_UCS4_strlen(buf);
    if (len + 5 > buflen)
        return NULL;
    buf[len] = '.'; len++;
    buf[len] = 'p'; len++;
    buf[len] = 'y'; len++;
    buf[len] = debug ? 'c' : 'o'; len++;
    assert(len <= buflen);
    return PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND, buf, len);
}


/* Given a pathname to a Python byte compiled file, return the path to the
   source file, if the path matches the PEP 3147 format.  This does not check
   for any file existence, however, if the pyc file name does not match PEP
   3147 style, NULL is returned.  buf must be at least as big as pathname;
   the resulting path will always be shorter.

   (...)/__pycache__/foo.<tag>.pyc -> (...)/foo.py */

static PyObject*
make_source_pathname(PyObject *pathobj)
{
    Py_UCS4 buf[MAXPATHLEN];
    Py_UCS4 *pathname;
    Py_UCS4 *left, *right, *dot0, *dot1, sep;
    size_t i, j;

    if (PyUnicode_GET_LENGTH(pathobj) > MAXPATHLEN)
        return NULL;
    pathname = PyUnicode_AsUCS4Copy(pathobj);
    if (!pathname)
        return NULL;

    /* Look back two slashes from the end.  In between these two slashes
       must be the string __pycache__ or this is not a PEP 3147 style
       path.  It's possible for there to be only one slash.
    */
    right = rightmost_sep(pathname);
    if (right == NULL)
        return NULL;
    sep = *right;
    *right = '\0';
    left = rightmost_sep(pathname);
    *right = sep;
    if (left == NULL)
        left = pathname;
    else
        left++;
    if (right-left != Py_UCS4_strlen(CACHEDIR_UNICODE) ||
        Py_UCS4_strncmp(left, CACHEDIR_UNICODE, right-left) != 0)
        goto error;

    /* Now verify that the path component to the right of the last slash
       has two dots in it.
    */
    if ((dot0 = Py_UCS4_strchr(right + 1, '.')) == NULL)
       goto error;
    if ((dot1 = Py_UCS4_strchr(dot0 + 1, '.')) == NULL)
        goto error;
    /* Too many dots? */
    if (Py_UCS4_strchr(dot1 + 1, '.') != NULL)
        goto error;

    /* This is a PEP 3147 path.  Start by copying everything from the
       start of pathname up to and including the leftmost slash.  Then
       copy the file's basename, removing the magic tag and adding a .py
       suffix.
    */
    Py_UCS4_strncpy(buf, pathname, (i=left-pathname));
    Py_UCS4_strncpy(buf+i, right+1, (j=dot0-right));
    buf[i+j] = 'p';
    buf[i+j+1] = 'y';
    PyMem_Free(pathname);
    return PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND, buf, i+j+2);
  error:
    PyMem_Free(pathname);
    return NULL;
}

/* Given a pathname for a Python source file, its time of last
   modification, and a pathname for a compiled file, check whether the
   compiled file represents the same version of the source.  If so,
   return a FILE pointer for the compiled file, positioned just after
   the header; if not, return NULL.
   Doesn't set an exception. */

static FILE *
check_compiled_module(PyObject *pathname, time_t mtime, PyObject *cpathname)
{
    FILE *fp;
    long magic;
    long pyc_mtime;

    fp = _Py_fopen(cpathname, "rb");
    if (fp == NULL)
        return NULL;
    magic = PyMarshal_ReadLongFromFile(fp);
    if (magic != pyc_magic) {
        if (Py_VerboseFlag)
            PySys_FormatStderr("# %R has bad magic\n", cpathname);
        fclose(fp);
        return NULL;
    }
    pyc_mtime = PyMarshal_ReadLongFromFile(fp);
    if (pyc_mtime != mtime) {
        if (Py_VerboseFlag)
            PySys_FormatStderr("# %R has bad mtime\n", cpathname);
        fclose(fp);
        return NULL;
    }
    if (Py_VerboseFlag)
        PySys_FormatStderr("# %R matches %R\n", cpathname, pathname);
    return fp;
}


/* Read a code object from a file and check it for validity */

static PyCodeObject *
read_compiled_module(PyObject *cpathname, FILE *fp)
{
    PyObject *co;

    co = PyMarshal_ReadLastObjectFromFile(fp);
    if (co == NULL)
        return NULL;
    if (!PyCode_Check(co)) {
        PyErr_Format(PyExc_ImportError,
                     "Non-code object in %R", cpathname);
        Py_DECREF(co);
        return NULL;
    }
    return (PyCodeObject *)co;
}


/* Load a module from a compiled file, execute it, and return its
   module object WITH INCREMENTED REFERENCE COUNT */

static PyObject *
load_compiled_module(PyObject *name, PyObject *cpathname, FILE *fp)
{
    long magic;
    PyCodeObject *co;
    PyObject *m;

    magic = PyMarshal_ReadLongFromFile(fp);
    if (magic != pyc_magic) {
        PyErr_Format(PyExc_ImportError,
                     "Bad magic number in %R", cpathname);
        return NULL;
    }
    (void) PyMarshal_ReadLongFromFile(fp);
    co = read_compiled_module(cpathname, fp);
    if (co == NULL)
        return NULL;
    if (Py_VerboseFlag)
        PySys_FormatStderr("import %U # precompiled from %R\n",
                           name, cpathname);
    m = PyImport_ExecCodeModuleObject(name, (PyObject *)co,
                                      cpathname, cpathname);
    Py_DECREF(co);

    return m;
}

/* Parse a source file and return the corresponding code object */

static PyCodeObject *
parse_source_module(PyObject *pathname, FILE *fp)
{
    PyCodeObject *co;
    PyObject *pathbytes;
    mod_ty mod;
    PyCompilerFlags flags;
    PyArena *arena;

    pathbytes = PyUnicode_EncodeFSDefault(pathname);
    if (pathbytes == NULL)
        return NULL;

    arena = PyArena_New();
    if (arena == NULL) {
        Py_DECREF(pathbytes);
        return NULL;
    }

    flags.cf_flags = 0;
    mod = PyParser_ASTFromFile(fp, PyBytes_AS_STRING(pathbytes), NULL,
                               Py_file_input, 0, 0, &flags,
                               NULL, arena);
    if (mod != NULL)
        co = PyAST_Compile(mod, PyBytes_AS_STRING(pathbytes), NULL, arena);
    else
        co = NULL;
    Py_DECREF(pathbytes);
    PyArena_Free(arena);
    return co;
}

/* Helper to open a bytecode file for writing in exclusive mode */

#ifndef MS_WINDOWS
static FILE *
open_exclusive(char *filename, mode_t mode)
{
#if defined(O_EXCL)&&defined(O_CREAT)&&defined(O_WRONLY)&&defined(O_TRUNC)
    /* Use O_EXCL to avoid a race condition when another process tries to
       write the same file.  When that happens, our open() call fails,
       which is just fine (since it's only a cache).
       XXX If the file exists and is writable but the directory is not
       writable, the file will never be written.  Oh well.
    */
    int fd;
    (void) unlink(filename);
    fd = open(filename, O_EXCL|O_CREAT|O_WRONLY|O_TRUNC
#ifdef O_BINARY
                            |O_BINARY   /* necessary for Windows */
#endif
#ifdef __VMS
            , mode, "ctxt=bin", "shr=nil"
#else
            , mode
#endif
          );
    if (fd < 0)
        return NULL;
    return fdopen(fd, "wb");
#else
    /* Best we can do -- on Windows this can't happen anyway */
    return fopen(filename, "wb");
#endif
}
#endif


/* Write a compiled module to a file, placing the time of last
   modification of its source into the header.
   Errors are ignored, if a write error occurs an attempt is made to
   remove the file. */

static void
write_compiled_module(PyCodeObject *co, PyObject *cpathname,
                      struct stat *srcstat)
{
    Py_UCS4 *cpathname_ucs4;
    FILE *fp;
    time_t mtime = srcstat->st_mtime;
#ifdef MS_WINDOWS   /* since Windows uses different permissions  */
    mode_t mode = srcstat->st_mode & ~S_IEXEC;
#else
    mode_t mode = srcstat->st_mode & ~S_IXUSR & ~S_IXGRP & ~S_IXOTH;
    mode_t dirmode = (srcstat->st_mode |
                      S_IXUSR | S_IXGRP | S_IXOTH |
                      S_IWUSR | S_IWGRP | S_IWOTH);
    PyObject *dirbytes;
#endif
#ifdef MS_WINDOWS
    int fd;
#else
    PyObject *cpathbytes;
#endif
    PyObject *dirname;
    Py_UCS4 *dirsep;
    int res, ok;

    /* Ensure that the __pycache__ directory exists. */
    cpathname_ucs4 = PyUnicode_AsUCS4Copy(cpathname);
    if (!cpathname_ucs4)
        return;
    dirsep = rightmost_sep(cpathname_ucs4);
    if (dirsep == NULL) {
        if (Py_VerboseFlag)
            PySys_FormatStderr("# no %s path found %R\n", CACHEDIR, cpathname);
        return;
    }
    dirname = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                        cpathname_ucs4,
                                        dirsep - cpathname_ucs4);
    PyMem_Free(cpathname_ucs4);
    if (dirname == NULL) {
        PyErr_Clear();
        return;
    }

#ifdef MS_WINDOWS
    res = CreateDirectoryW(PyUnicode_AS_UNICODE(dirname), NULL);
    ok = (res != 0);
    if (!ok && GetLastError() == ERROR_ALREADY_EXISTS)
        ok = 1;
#else
    dirbytes = PyUnicode_EncodeFSDefault(dirname);
    if (dirbytes == NULL) {
        PyErr_Clear();
        return;
    }
    res = mkdir(PyBytes_AS_STRING(dirbytes), dirmode);
    Py_DECREF(dirbytes);
    if (0 <= res)
        ok = 1;
    else
        ok = (errno == EEXIST);
#endif
    if (!ok) {
        if (Py_VerboseFlag)
            PySys_FormatStderr("# cannot create cache dir %R\n", dirname);
        Py_DECREF(dirname);
        return;
    }
    Py_DECREF(dirname);

#ifdef MS_WINDOWS
    (void)DeleteFileW(PyUnicode_AS_UNICODE(cpathname));
    fd = _wopen(PyUnicode_AS_UNICODE(cpathname),
                 O_EXCL | O_CREAT | O_WRONLY | O_TRUNC | O_BINARY,
                 mode);
    if (0 <= fd)
        fp = fdopen(fd, "wb");
    else
        fp = NULL;
#else
    cpathbytes = PyUnicode_EncodeFSDefault(cpathname);
    if (cpathbytes == NULL) {
        PyErr_Clear();
        return;
    }

    fp = open_exclusive(PyBytes_AS_STRING(cpathbytes), mode);
#endif
    if (fp == NULL) {
        if (Py_VerboseFlag)
            PySys_FormatStderr(
                "# can't create %R\n", cpathname);
#ifndef MS_WINDOWS
        Py_DECREF(cpathbytes);
#endif
        return;
    }
    PyMarshal_WriteLongToFile(pyc_magic, fp, Py_MARSHAL_VERSION);
    /* First write a 0 for mtime */
    PyMarshal_WriteLongToFile(0L, fp, Py_MARSHAL_VERSION);
    PyMarshal_WriteObjectToFile((PyObject *)co, fp, Py_MARSHAL_VERSION);
    if (fflush(fp) != 0 || ferror(fp)) {
        if (Py_VerboseFlag)
            PySys_FormatStderr("# can't write %R\n", cpathname);
        /* Don't keep partial file */
        fclose(fp);
#ifdef MS_WINDOWS
        (void)DeleteFileW(PyUnicode_AS_UNICODE(cpathname));
#else
        (void) unlink(PyBytes_AS_STRING(cpathbytes));
        Py_DECREF(cpathbytes);
#endif
        return;
    }
#ifndef MS_WINDOWS
    Py_DECREF(cpathbytes);
#endif
    /* Now write the true mtime */
    fseek(fp, 4L, 0);
    assert(mtime < LONG_MAX);
    PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);
    fflush(fp);
    fclose(fp);
    if (Py_VerboseFlag)
        PySys_FormatStderr("# wrote %R\n", cpathname);
}

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;
}

/* Load a source module from a given file and return its module
   object WITH INCREMENTED REFERENCE COUNT.  If there's a matching
   byte-compiled file, use that instead. */

static PyObject *
load_source_module(PyObject *name, PyObject *pathname, FILE *fp)
{
    struct stat st;
    FILE *fpc;
    PyObject *cpathname = NULL, *cpathbytes = NULL;
    PyCodeObject *co;
    PyObject *m = NULL;

    if (fstat(fileno(fp), &st) != 0) {
        PyErr_Format(PyExc_RuntimeError,
                     "unable to get file status from %R",
                     pathname);
        goto error;
    }
#if SIZEOF_TIME_T > 4
    /* Python's .pyc timestamp handling presumes that the timestamp fits
       in 4 bytes. This will be fine until sometime in the year 2038,
       when a 4-byte signed time_t will overflow.
     */
    if (st.st_mtime >> 32) {
        PyErr_SetString(PyExc_OverflowError,
            "modification time overflows a 4 byte field");
        goto error;
    }
#endif
    cpathname = make_compiled_pathname(pathname, !Py_OptimizeFlag);

    if (cpathname != NULL)
        fpc = check_compiled_module(pathname, st.st_mtime, cpathname);
    else
        fpc = NULL;

    if (fpc) {
        co = read_compiled_module(cpathname, fpc);
        fclose(fpc);
        if (co == NULL)
            goto error;
        update_compiled_module(co, pathname);
        if (Py_VerboseFlag)
            PySys_FormatStderr("import %U # precompiled from %R\n",
                               name, cpathname);
        m = PyImport_ExecCodeModuleObject(name, (PyObject *)co,
                                          cpathname, cpathname);
    }
    else {
        co = parse_source_module(pathname, fp);
        if (co == NULL)
            goto error;
        if (Py_VerboseFlag)
            PySys_FormatStderr("import %U # from %R\n",
                               name, pathname);
        if (cpathname != NULL) {
            PyObject *ro = PySys_GetObject("dont_write_bytecode");
            if (ro == NULL || !PyObject_IsTrue(ro))
                write_compiled_module(co, cpathname, &st);
        }
        m = PyImport_ExecCodeModuleObject(name, (PyObject *)co,
                                          pathname, cpathname);
    }
    Py_DECREF(co);

error:
    Py_XDECREF(cpathbytes);
    Py_XDECREF(cpathname);
    return m;
}

/* Get source file -> unicode or None
 * Returns the path to the py file if available, else the given path
 */
static PyObject *
get_sourcefile(PyObject *filename)
{
    Py_ssize_t len;
    Py_UCS4 *fileuni;
    PyObject *py;
    struct stat statbuf;

    len = PyUnicode_GET_LENGTH(filename);
    if (len == 0)
        Py_RETURN_NONE;

    /* don't match *.pyc or *.pyo? */
    fileuni = PyUnicode_AsUCS4Copy(filename);
    if (!fileuni)
        return NULL;
    if (len < 5
        || fileuni[len-4] != '.'
        || (fileuni[len-3] != 'p' && fileuni[len-3] != 'P')
        || (fileuni[len-2] != 'y' && fileuni[len-2] != 'Y'))
        goto unchanged;

    /* Start by trying to turn PEP 3147 path into source path.  If that
     * fails, just chop off the trailing character, i.e. legacy pyc path
     * to py.
     */
    py = make_source_pathname(filename);
    if (py == NULL) {
        PyErr_Clear();
        py = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND, fileuni, len - 1);
    }
    if (py == NULL)
        goto error;

    if (_Py_stat(py, &statbuf) == 0 && S_ISREG(statbuf.st_mode))
        return py;
    Py_DECREF(py);
    goto unchanged;

error:
    PyErr_Clear();
unchanged:
    PyMem_Free(fileuni);
    Py_INCREF(filename);
    return filename;
}

/* Forward */
static PyObject *load_module(PyObject *, FILE *, PyObject *, int, PyObject *);
static struct filedescr *find_module(PyObject *, PyObject *, PyObject *,
                                     PyObject **, FILE **, PyObject **);
static struct _frozen * find_frozen(PyObject *);

/* Load a package and return its module object WITH INCREMENTED
   REFERENCE COUNT */

static PyObject *
load_package(PyObject *name, PyObject *pathname)
{
    PyObject *m, *d, *bufobj;
    PyObject *file = NULL, *path_list = NULL;
    int err;
    FILE *fp = NULL;
    struct filedescr *fdp;

    m = PyImport_AddModuleObject(name);
    if (m == NULL)
        return NULL;
    if (Py_VerboseFlag)
        PySys_FormatStderr("import %U # directory %R\n",
                           name, pathname);
    file = get_sourcefile(pathname);
    if (file == NULL)
        return NULL;
    path_list = Py_BuildValue("[O]", file);
    if (path_list == NULL) {
        Py_DECREF(file);
        return NULL;
    }
    d = PyModule_GetDict(m);
    err = PyDict_SetItemString(d, "__file__", file);
    Py_DECREF(file);
    if (err == 0)
        err = PyDict_SetItemString(d, "__path__", path_list);
    if (err != 0) {
        Py_DECREF(path_list);
        return NULL;
    }
    fdp = find_module(name, initstr, path_list,
                      &bufobj, &fp, NULL);
    Py_DECREF(path_list);
    if (fdp == NULL) {
        if (PyErr_ExceptionMatches(PyExc_ImportError)) {
            PyErr_Clear();
            Py_INCREF(m);
            return m;
        }
        else
            return NULL;
    }
    m = load_module(name, fp, bufobj, fdp->type, NULL);
    Py_XDECREF(bufobj);
    if (fp != NULL)
        fclose(fp);
    return m;
}


/* 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) {
        importer = PyObject_CallFunctionObjArgs(
            (PyObject *)&PyNullImporter_Type, p, NULL
        );
        if (importer == NULL) {
            if (PyErr_ExceptionMatches(PyExc_ImportError)) {
                PyErr_Clear();
                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;
}

/* Search the path (default sys.path) for a module.  Return the
   corresponding filedescr struct, and (via return arguments) the
   pathname and an open file.  Return NULL if the module is not found. */

#ifdef MS_COREDLL
extern FILE *_PyWin_FindRegisteredModule(PyObject *, struct filedescr **,
                                         PyObject **p_path);
#endif

/* Forward */
static int case_ok(PyObject *, Py_ssize_t, PyObject *);
static int find_init_module(PyObject *);
static struct filedescr importhookdescr = {"", "", IMP_HOOK};

/* Get the path of a module: get its importer and call importer.find_module()
   hook, or check if the module if a package (if path/__init__.py exists).

    -1: error: a Python error occurred
     0: ignore: an error occurred because of invalid data, but the error is not
        important enough to be reported.
     1: get path: module not found, but *buf contains its path
     2: found: *p_fd is the file descriptor (IMP_HOOK or PKG_DIRECTORY)
        and *buf is the path */

static int
find_module_path(PyObject *fullname, PyObject *name, PyObject *path,
                 PyObject *path_hooks, PyObject *path_importer_cache,
                 PyObject **p_path, PyObject **p_loader, struct filedescr **p_fd)
{
    Py_UCS4 buf[MAXPATHLEN+1];
    PyObject *path_unicode, *filename;
    Py_ssize_t len;
    struct stat statbuf;
    static struct filedescr fd_package = {"", "", PKG_DIRECTORY};

    if (PyUnicode_Check(path)) {
        Py_INCREF(path);
        path_unicode = path;
    }
    else if (PyBytes_Check(path)) {
        path_unicode = PyUnicode_DecodeFSDefaultAndSize(
            PyBytes_AS_STRING(path), PyBytes_GET_SIZE(path));
        if (path_unicode == NULL)
            return -1;
    }
    else
        return 0;

    len = PyUnicode_GET_LENGTH(path_unicode);
    if (!PyUnicode_AsUCS4(path_unicode, buf, Py_ARRAY_LENGTH(buf), 1)) {
        Py_DECREF(path_unicode);
        PyErr_Clear();
        return 0;
    }
    Py_DECREF(path_unicode);

    if (Py_UCS4_strlen(buf) != len)
        return 0; /* path contains '\0' */

    /* sys.path_hooks import hook */
    if (p_loader != NULL) {
        PyObject *importer;

        importer = get_path_importer(path_importer_cache,
                                     path_hooks, path);
        if (importer == NULL) {
            return -1;
        }
        /* Note: importer is a borrowed reference */
        if (importer != Py_None) {
            PyObject *loader;
            loader = PyObject_CallMethod(importer,
                                         "find_module", "O", fullname);
            if (loader == NULL)
                return -1;  /* error */
            if (loader != Py_None) {
                /* a loader was found */
                *p_loader = loader;
                *p_fd = &importhookdescr;
                return 2;
            }
            Py_DECREF(loader);
            return 0;
        }
    }
    /* no hook was found, use builtin import */

    if (len > 0 && buf[len-1] != SEP
#ifdef ALTSEP
        && buf[len-1] != ALTSEP
#endif
        )
        buf[len++] = SEP;
    if (!PyUnicode_AsUCS4(name, buf+len, Py_ARRAY_LENGTH(buf)-len, 1)) {
        PyErr_Clear();
        return 0;
    }
    len += PyUnicode_GET_LENGTH(name);

    filename = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                         buf, len);
    if (filename == NULL)
        return -1;

    /* Check for package import (buf holds a directory name,
       and there's an __init__ module in that directory */
#ifdef HAVE_STAT
    if (_Py_stat(filename, &statbuf) == 0 &&         /* it exists */
        S_ISDIR(statbuf.st_mode))           /* it's a directory */
    {
        int match;

        match = case_ok(filename, 0, name);
        if (match < 0) {
            Py_DECREF(filename);
            return -1;
        }
        if (match) { /* case matches */
            if (find_init_module(filename)) { /* and has __init__.py */
                *p_path = filename;
                *p_fd = &fd_package;
                return 2;
            }
            else {
                int err;
                err = PyErr_WarnFormat(PyExc_ImportWarning, 1,
                    "Not importing directory %R: missing __init__.py",
                    filename);
                if (err) {
                    Py_DECREF(filename);
                    return -1;
                }
            }
        }
    }
#endif
    *p_path = filename;
    return 1;
}

/* Find a module in search_path_list. For each path, try
   find_module_path() or try each _PyImport_Filetab suffix.

   If the module is found, return a file descriptor, write the path in
   *p_filename, write the pointer to the file object into *p_fp, and (if
   p_loader is not NULL) the loader into *p_loader.

   Otherwise, raise an exception and return NULL. */

static struct filedescr*
find_module_path_list(PyObject *fullname, PyObject *name,
                      PyObject *search_path_list, PyObject *path_hooks,
                      PyObject *path_importer_cache,
                      PyObject **p_path, FILE **p_fp, PyObject **p_loader)
{
    Py_ssize_t i, npath;
    struct filedescr *fdp = NULL;
    char *filemode;
    FILE *fp = NULL;
    PyObject *prefix, *filename;
    int match;

    npath = PyList_Size(search_path_list);
    for (i = 0; i < npath; i++) {
        PyObject *path;
        int ok;

        path = PyList_GetItem(search_path_list, i);
        if (path == NULL)
            return NULL;

        prefix = NULL;
        ok = find_module_path(fullname, name, path,
                              path_hooks, path_importer_cache,
                              &prefix, p_loader, &fdp);
        if (ok < 0)
            return NULL;
        if (ok == 0)
            continue;
        if (ok == 2) {
            *p_path = prefix;
            return fdp;
        }

        for (fdp = _PyImport_Filetab; fdp->suffix != NULL; fdp++) {
            struct stat statbuf;

            filemode = fdp->mode;
            if (filemode[0] == 'U')
                filemode = "r" PY_STDIOTEXTMODE;

            filename = PyUnicode_FromFormat("%U%s", prefix, fdp->suffix);
            if (filename == NULL) {
                Py_DECREF(prefix);
                return NULL;
            }

            if (Py_VerboseFlag > 1)
                PySys_FormatStderr("# trying %R\n", filename);

            if (_Py_stat(filename, &statbuf) == 0 &&         /* it exists */
                S_ISDIR(statbuf.st_mode))           /* it's a directory */
            {
                Py_DECREF(filename);
                continue;
            }

            fp = _Py_fopen(filename, filemode);
            if (fp == NULL) {
                Py_DECREF(filename);
                if (PyErr_Occurred()) {
                    Py_DECREF(prefix);
                    return NULL;
                }
                continue;
            }
            match = case_ok(filename, -(Py_ssize_t)strlen(fdp->suffix), name);
            if (match < 0) {
                Py_DECREF(prefix);
                Py_DECREF(filename);
                return NULL;
            }
            if (match) {
                Py_DECREF(prefix);
                *p_path = filename;
                *p_fp = fp;
                return fdp;
            }
            Py_DECREF(filename);

            fclose(fp);
            fp = NULL;
        }
        Py_DECREF(prefix);
    }
    PyErr_Format(PyExc_ImportError,
                 "No module named %R", name);
    return NULL;
}

/* Find a module:

   - try find_module() of each sys.meta_path hook
   - try find_frozen()
   - try is_builtin()
   - try _PyWin_FindRegisteredModule() (Windows only)
   - otherwise, call find_module_path_list() with search_path_list (if not
     NULL) or sys.path

   fullname can be NULL, but only if p_loader is NULL.

   Return:

   - &fd_builtin (C_BUILTIN) if it is a builtin
   - &fd_frozen (PY_FROZEN) if it is frozen
   - &fd_package (PKG_DIRECTORY) and write the filename into *p_path
     if it is a package
   - &importhookdescr (IMP_HOOK) and write the loader into *p_loader if a
     importer loader was found
   - a file descriptor (PY_SOURCE, PY_COMPILED, C_EXTENSION, PY_RESOURCE or
     PY_CODERESOURCE: see _PyImport_Filetab), write the filename into
     *p_path and the pointer to the open file into *p_fp
   - NULL on error

   By default, *p_path, *p_fp and *p_loader (if set) are set to NULL.
   Eg. *p_path is set to NULL for a builtin package.
*/

static struct filedescr *
find_module(PyObject *fullname, PyObject *name, PyObject *search_path_list,
            PyObject **p_path, FILE **p_fp, PyObject **p_loader)
{
    Py_ssize_t i, npath;
    static struct filedescr fd_frozen = {"", "", PY_FROZEN};
    static struct filedescr fd_builtin = {"", "", C_BUILTIN};
    PyObject *path_hooks, *path_importer_cache;

    *p_path = NULL;
    *p_fp = NULL;
    if (p_loader != NULL)
        *p_loader = NULL;

    if (PyUnicode_GET_LENGTH(name) > MAXPATHLEN) {
        PyErr_SetString(PyExc_OverflowError,
                        "module name is too long");
        return NULL;
    }

    /* sys.meta_path import hook */
    if (p_loader != NULL) {
        PyObject *meta_path;

        meta_path = PySys_GetObject("meta_path");
        if (meta_path == NULL || !PyList_Check(meta_path)) {
            PyErr_SetString(PyExc_RuntimeError,
                            "sys.meta_path must be a list of "
                            "import hooks");
            return NULL;
        }
        Py_INCREF(meta_path);  /* zap guard */
        npath = PyList_Size(meta_path);
        for (i = 0; i < npath; i++) {
            PyObject *loader;
            PyObject *hook = PyList_GetItem(meta_path, i);
            loader = PyObject_CallMethod(hook, "find_module",
                                         "OO", fullname,
                                         search_path_list != NULL ?
                                         search_path_list : Py_None);
            if (loader == NULL) {
                Py_DECREF(meta_path);
                return NULL;  /* true error */
            }
            if (loader != Py_None) {
                /* a loader was found */
                *p_loader = loader;
                Py_DECREF(meta_path);
                return &importhookdescr;
            }
            Py_DECREF(loader);
        }
        Py_DECREF(meta_path);
    }

    if (find_frozen(fullname) != NULL)
        return &fd_frozen;

    if (search_path_list == NULL) {
#ifdef MS_COREDLL
        FILE *fp;
        struct filedescr *fdp;
#endif
        if (is_builtin(name))
            return &fd_builtin;
#ifdef MS_COREDLL
        fp = _PyWin_FindRegisteredModule(name, &fdp, p_path);
        if (fp != NULL) {
            *p_fp = fp;
            return fdp;
        }
        else if (PyErr_Occurred())
            return NULL;
#endif
        search_path_list = PySys_GetObject("path");
    }

    if (search_path_list == NULL || !PyList_Check(search_path_list)) {
        PyErr_SetString(PyExc_RuntimeError,
                        "sys.path must be a list of directory names");
        return NULL;
    }

    path_hooks = PySys_GetObject("path_hooks");
    if (path_hooks == NULL || !PyList_Check(path_hooks)) {
        PyErr_SetString(PyExc_RuntimeError,
                        "sys.path_hooks must be a list of "
                        "import hooks");
        return NULL;
    }
    path_importer_cache = PySys_GetObject("path_importer_cache");
    if (path_importer_cache == NULL ||
        !PyDict_Check(path_importer_cache)) {
        PyErr_SetString(PyExc_RuntimeError,
                        "sys.path_importer_cache must be a dict");
        return NULL;
    }

    return find_module_path_list(fullname, name,
                                 search_path_list, path_hooks,
                                 path_importer_cache,
                                 p_path, p_fp, p_loader);
}

/* case_bytes(char* buf, Py_ssize_t len, Py_ssize_t namelen, char* name)
 * The arguments here are tricky, best shown by example:
 *    /a/b/c/d/e/f/g/h/i/j/k/some_long_module_name.py\0
 *    ^                      ^                   ^    ^
 *    |--------------------- buf ---------------------|
 *    |------------------- len ------------------|
 *                           |------ name -------|
 *                           |----- namelen -----|
 * buf is the full path, but len only counts up to (& exclusive of) the
 * extension.  name is the module name, also exclusive of extension.
 *
 * We've already done a successful stat() or fopen() on buf, so know that
 * there's some match, possibly case-insensitive.
 *
 * case_bytes() is to return 1 if there's a case-sensitive match for
 * name, else 0.  case_bytes() is also to return 1 if envar PYTHONCASEOK
 * exists.
 *
 * case_bytes() is used to implement case-sensitive import semantics even
 * on platforms with case-insensitive filesystems.  It's trivial to implement
 * for case-sensitive filesystems.  It's pretty much a cross-platform
 * nightmare for systems with case-insensitive filesystems.
 */

/* First we may need a pile of platform-specific header files; the sequence
 * of #if's here should match the sequence in the body of case_bytes().
 */
#if defined(MS_WINDOWS)
#include <windows.h>

#elif defined(DJGPP)
#include <dir.h>

#elif (defined(__MACH__) && defined(__APPLE__) || defined(__CYGWIN__)) && defined(HAVE_DIRENT_H)
#include <sys/types.h>
#include <dirent.h>

#elif defined(PYOS_OS2)
#define INCL_DOS
#define INCL_DOSERRORS
#define INCL_NOPMAPI
#include <os2.h>
#endif

#if defined(DJGPP) \
    || ((defined(__MACH__) && defined(__APPLE__) || defined(__CYGWIN__)) \
        && defined(HAVE_DIRENT_H)) \
    || defined(PYOS_OS2)
#  define USE_CASE_OK_BYTES
#endif


#ifdef USE_CASE_OK_BYTES
static int
case_bytes(char *buf, Py_ssize_t len, Py_ssize_t namelen, const char *name)
{
/* Pick a platform-specific implementation; the sequence of #if's here should
 * match the sequence just above.
 */

/* DJGPP */
#if defined(DJGPP)
    struct ffblk ffblk;
    int done;

    if (Py_GETENV("PYTHONCASEOK") != NULL)
        return 1;

    done = findfirst(buf, &ffblk, FA_ARCH|FA_RDONLY|FA_HIDDEN|FA_DIREC);
    if (done) {
        PyErr_Format(PyExc_NameError,
          "Can't find file for module %.100s\n(filename %.300s)",
          name, buf);
        return -1;
    }
    return strncmp(ffblk.ff_name, name, namelen) == 0;

/* new-fangled macintosh (macosx) or Cygwin */
#elif (defined(__MACH__) && defined(__APPLE__) || defined(__CYGWIN__)) && defined(HAVE_DIRENT_H)
    DIR *dirp;
    struct dirent *dp;
    char dirname[MAXPATHLEN + 1];
    const int dirlen = len - namelen - 1; /* don't want trailing SEP */

    if (Py_GETENV("PYTHONCASEOK") != NULL)
        return 1;

    /* Copy the dir component into dirname; substitute "." if empty */
    if (dirlen <= 0) {
        dirname[0] = '.';
        dirname[1] = '\0';
    }
    else {
        assert(dirlen <= MAXPATHLEN);
        memcpy(dirname, buf, dirlen);
        dirname[dirlen] = '\0';
    }
    /* Open the directory and search the entries for an exact match. */
    dirp = opendir(dirname);
    if (dirp) {
        char *nameWithExt = buf + len - namelen;
        while ((dp = readdir(dirp)) != NULL) {
            const int thislen =
#ifdef _DIRENT_HAVE_D_NAMELEN
                                    dp->d_namlen;
#else
                                    strlen(dp->d_name);
#endif
            if (thislen >= namelen &&
                strcmp(dp->d_name, nameWithExt) == 0) {
                (void)closedir(dirp);
                return 1; /* Found */
            }
        }
        (void)closedir(dirp);
    }
    return 0 ; /* Not found */

/* OS/2 */
#elif defined(PYOS_OS2)
    HDIR hdir = 1;
    ULONG srchcnt = 1;
    FILEFINDBUF3 ffbuf;
    APIRET rc;

    if (Py_GETENV("PYTHONCASEOK") != NULL)
        return 1;

    rc = DosFindFirst(buf,
                      &hdir,
                      FILE_READONLY | FILE_HIDDEN | FILE_SYSTEM | FILE_DIRECTORY,
                      &ffbuf, sizeof(ffbuf),
                      &srchcnt,
                      FIL_STANDARD);
    if (rc != NO_ERROR)
        return 0;
    return strncmp(ffbuf.achName, name, namelen) == 0;

/* assuming it's a case-sensitive filesystem, so there's nothing to do! */
#else
#   error "USE_CASE_OK_BYTES is not correctly defined"
#endif
}
#endif

/*
 * Check if a filename case matchs the name case. We've already done a
 * successful stat() or fopen() on buf, so know that there's some match,
 * possibly case-insensitive.
 *
 * case_ok() is to return 1 if there's a case-sensitive match for name, 0 if it
 * the filename doesn't match, or -1 on error.  case_ok() is also to return 1
 * if envar PYTHONCASEOK exists.
 *
 * case_ok() is used to implement case-sensitive import semantics even
 * on platforms with case-insensitive filesystems.  It's trivial to implement
 * for case-sensitive filesystems.  It's pretty much a cross-platform
 * nightmare for systems with case-insensitive filesystems.
 */

static int
case_ok(PyObject *filename, Py_ssize_t prefix_delta, PyObject *name)
{
#ifdef MS_WINDOWS
    WIN32_FIND_DATAW data;
    HANDLE h;
    int cmp;

    if (Py_GETENV("PYTHONCASEOK") != NULL)
        return 1;

    h = FindFirstFileW(PyUnicode_AS_UNICODE(filename), &data);
    if (h == INVALID_HANDLE_VALUE) {
        PyErr_Format(PyExc_NameError,
          "Can't find file for module %R\n(filename %R)",
          name, filename);
        return 0;
    }
    FindClose(h);
    cmp = wcsncmp(data.cFileName,
                  PyUnicode_AS_UNICODE(name),
                  PyUnicode_GET_SIZE(name));
    return cmp == 0;
#elif defined(USE_CASE_OK_BYTES)
    int match;
    PyObject *filebytes, *namebytes;
    filebytes = PyUnicode_EncodeFSDefault(filename);
    if (filebytes == NULL)
        return -1;
    namebytes = PyUnicode_EncodeFSDefault(name);
    if (namebytes == NULL) {
        Py_DECREF(filebytes);
        return -1;
    }
    match = case_bytes(
        PyBytes_AS_STRING(filebytes),
        PyBytes_GET_SIZE(filebytes) + prefix_delta,
        PyBytes_GET_SIZE(namebytes),
        PyBytes_AS_STRING(namebytes));
    Py_DECREF(filebytes);
    Py_DECREF(namebytes);
    return match;
#else
    /* assuming it's a case-sensitive filesystem, so there's nothing to do! */
    return 1;

#endif
}

#ifdef HAVE_STAT

/* Helper to look for __init__.py or __init__.py[co] in potential package.
   Return 1 if __init__ was found, 0 if not, or -1 on error. */
static int
find_init_module(PyObject *directory)
{
    struct stat statbuf;
    PyObject *filename;
    int match;

    filename = PyUnicode_FromFormat("%U%c__init__.py", directory, SEP);
    if (filename == NULL)
        return -1;
    if (_Py_stat(filename, &statbuf) == 0) {
        /* 3=len(".py") */
        match = case_ok(filename, -3, initstr);
        if (match < 0) {
            Py_DECREF(filename);
            return -1;
        }
        if (match) {
            Py_DECREF(filename);
            return 1;
        }
    }
    Py_DECREF(filename);

    filename = PyUnicode_FromFormat("%U%c__init__.py%c",
        directory, SEP, Py_OptimizeFlag ? 'o' : 'c');
    if (filename == NULL)
        return -1;
    if (_Py_stat(filename, &statbuf) == 0) {
        /* 4=len(".pyc") */
        match = case_ok(filename, -4, initstr);
        if (match < 0) {
            Py_DECREF(filename);
            return -1;
        }
        if (match) {
            Py_DECREF(filename);
            return 1;
        }
    }
    Py_DECREF(filename);
    return 0;
}

#endif /* HAVE_STAT */


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

static PyObject*
load_builtin(PyObject *name, int type)
{
    PyObject *m, *modules;
    int err;

    if (type == C_BUILTIN)
        err = init_builtin(name);
    else
        err = PyImport_ImportFrozenModuleObject(name);
    if (err < 0)
        return NULL;
    if (err == 0) {
        PyErr_Format(PyExc_ImportError,
                "Purported %s module %R not found",
                type == C_BUILTIN ? "builtin" : "frozen",
                name);
        return NULL;
    }

    modules = PyImport_GetModuleDict();
    m = PyDict_GetItem(modules, name);
    if (m == NULL) {
        PyErr_Format(
                PyExc_ImportError,
                "%s module %R not properly initialized",
                type == C_BUILTIN ? "builtin" : "frozen",
                name);
        return NULL;
    }
    Py_INCREF(m);
    return m;
}

/* Load an external module using the default search path and return
   its module object WITH INCREMENTED REFERENCE COUNT */

static PyObject *
load_module(PyObject *name, FILE *fp, PyObject *pathname, int type, PyObject *loader)
{
    PyObject *m;

    /* First check that there's an open file (if we need one)  */
    switch (type) {
    case PY_SOURCE:
    case PY_COMPILED:
        if (fp == NULL) {
            PyErr_Format(PyExc_ValueError,
                         "file object required for import (type code %d)",
                         type);
            return NULL;
        }
    }

    switch (type) {

    case PY_SOURCE:
        m = load_source_module(name, pathname, fp);
        break;

    case PY_COMPILED:
        m = load_compiled_module(name, pathname, fp);
        break;

#ifdef HAVE_DYNAMIC_LOADING
    case C_EXTENSION:
        m = _PyImport_LoadDynamicModule(name, pathname, fp);
        break;
#endif

    case PKG_DIRECTORY:
        m = load_package(name, pathname);
        break;

    case C_BUILTIN:
    case PY_FROZEN:
        m = load_builtin(name, type);
        break;

    case IMP_HOOK: {
        if (loader == NULL) {
            PyErr_SetString(PyExc_ImportError,
                            "import hook without loader");
            return NULL;
        }
        m = PyObject_CallMethod(loader, "load_module", "O", name);
        break;
    }

    default:
        PyErr_Format(PyExc_ImportError,
                     "Don't know how to import %R (type code %d)",
                      name, type);
        m = NULL;

    }

    return m;
}


/* 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;
        if (PyUnicode_CompareWithASCIIString(name, p->name) == 0) {
            if (p->initfunc == NULL) {
                PyErr_Format(PyExc_ImportError,
                    "Cannot re-init internal module %R",
                    name);
                return -1;
            }
            if (Py_VerboseFlag)
                PySys_FormatStderr("import %U # builtin\n", name);
            mod = (*p->initfunc)();
            if (mod == 0)
                return -1;
            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;
    if (Py_VerboseFlag)
        PySys_FormatStderr("import %U # frozen%s\n",
            name, ispackage ? " package" : "");
    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)
{
    PyObject *nameobj, *modules, *result;
#ifdef WITH_THREAD
    long me;
#endif

    /* Try to get the module from sys.modules[name] */
    modules = PyImport_GetModuleDict();
    if (modules == NULL)
        return NULL;

    nameobj = PyUnicode_FromString(name);
    if (nameobj == NULL)
        return NULL;
    result = PyDict_GetItem(modules, nameobj);
    if (result != NULL) {
        Py_DECREF(nameobj);
        Py_INCREF(result);
        return result;
    }
    PyErr_Clear();
#ifdef WITH_THREAD
    /* check the import lock
     * me might be -1 but I ignore the error here, the lock function
     * takes care of the problem */
    me = PyThread_get_thread_ident();
    if (import_lock_thread == -1 || import_lock_thread == me) {
        /* no thread or me is holding the lock */
        result = PyImport_Import(nameobj);
    }
    else {
        PyErr_Format(PyExc_ImportError,
                     "Failed to import %R because the import lock"
                     "is held by another thread.",
                     nameobj);
        result = NULL;
    }
#else
    result = PyImport_Import(nameobj);
#endif
    Py_DECREF(nameobj);
    return result;
}

/* Forward declarations for helper routines */
static PyObject *get_parent(PyObject *globals,
                            PyObject **p_name,
                            int level);
static PyObject *load_next(PyObject *mod, PyObject *altmod,
                           PyObject *inputname, PyObject **p_outputname,
                           Py_UCS4 *buf, Py_ssize_t *p_buflen,
                           Py_ssize_t bufsize);
static int mark_miss(PyObject *name);
static int ensure_fromlist(PyObject *mod, PyObject *fromlist,
                           PyObject *buf, int recursive);
static PyObject * import_submodule(PyObject *mod, PyObject *name,
                                   PyObject *fullname);

/* The Magnum Opus of dotted-name import :-) */

static PyObject *
import_module_level(PyObject *name, PyObject *globals, PyObject *locals,
                    PyObject *fromlist, int level)
{
    Py_UCS4 buf[MAXPATHLEN+1];
    Py_ssize_t buflen;
    Py_ssize_t bufsize = MAXPATHLEN+1;
    PyObject *parent, *head, *next, *tail, *inputname, *outputname;
    PyObject *parent_name, *ensure_name;
    Py_ssize_t sep, altsep;

    if (PyUnicode_READY(name))
        return NULL;

    sep = PyUnicode_FindChar(name, SEP, 0, PyUnicode_GET_LENGTH(name), 1);
    if (sep == -2)
        return NULL;
#ifdef ALTSEP
    altsep = PyUnicode_FindChar(name, ALTSEP, 0, PyUnicode_GET_LENGTH(name), 1);
    if (altsep == -2)
        return NULL;
#else
    altsep = -1;
#endif
    if (sep != -1 || altsep != -1)
    {
        PyErr_SetString(PyExc_ImportError,
                        "Import by filename is not supported.");
        return NULL;
    }

    parent = get_parent(globals, &parent_name, level);
    if (parent == NULL) {
        return NULL;
    }

    if (PyUnicode_READY(parent_name))
        return NULL;
    buflen = PyUnicode_GET_LENGTH(parent_name);
    if (!PyUnicode_AsUCS4(parent_name, buf, Py_ARRAY_LENGTH(buf), 1)) {
        Py_DECREF(parent_name);
        PyErr_SetString(PyExc_ValueError,
                        "Module name too long");
        return NULL;
    }
    Py_DECREF(parent_name);

    head = load_next(parent, level < 0 ? Py_None : parent, name, &outputname,
                     buf, &buflen, bufsize);
    if (head == NULL)
        return NULL;

    tail = head;
    Py_INCREF(tail);

    if (outputname != NULL) {
        while (1) {
            inputname = outputname;
            next = load_next(tail, tail, inputname, &outputname,
                             buf, &buflen, bufsize);
            Py_DECREF(tail);
            Py_DECREF(inputname);
            if (next == NULL) {
                Py_DECREF(head);
                return NULL;
            }
            tail = next;

            if (outputname == NULL) {
                break;
            }
        }
    }
    if (tail == Py_None) {
        /* If tail is Py_None, both get_parent and load_next found
           an empty module name: someone called __import__("") or
           doctored faulty bytecode */
        Py_DECREF(tail);
        Py_DECREF(head);
        PyErr_SetString(PyExc_ValueError, "Empty module name");
        return NULL;
    }

    if (fromlist != NULL) {
        if (fromlist == Py_None || !PyObject_IsTrue(fromlist))
            fromlist = NULL;
    }

    if (fromlist == NULL) {
        Py_DECREF(tail);
        return head;
    }

    Py_DECREF(head);

    ensure_name = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                            buf, Py_UCS4_strlen(buf));
    if (ensure_name == NULL) {
        Py_DECREF(tail);
        return NULL;
    }
    if (!ensure_fromlist(tail, fromlist, ensure_name, 0)) {
        Py_DECREF(tail);
        Py_DECREF(ensure_name);
        return NULL;
    }
    Py_DECREF(ensure_name);

    return tail;
}

PyObject *
PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                                 PyObject *locals, PyObject *fromlist,
                                 int level)
{
    PyObject *mod;
    _PyImport_AcquireLock();
    mod = import_module_level(name, globals, locals, fromlist, level);
    if (_PyImport_ReleaseLock() < 0) {
        Py_XDECREF(mod);
        PyErr_SetString(PyExc_RuntimeError,
                        "not holding the import lock");
        return NULL;
    }
    return 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;
}


/* Return the package that an import is being performed in.  If globals comes
   from the module foo.bar.bat (not itself a package), this returns the
   sys.modules entry for foo.bar.  If globals is from a package's __init__.py,
   the package's entry in sys.modules is returned, as a borrowed reference.

   The name of the returned package is returned in *p_name.

   If globals doesn't come from a package or a module in a package, or a
   corresponding entry is not found in sys.modules, Py_None is returned.
*/
static PyObject *
get_parent(PyObject *globals, PyObject **p_name, int level)
{
    PyObject *nameobj;

    static PyObject *namestr = NULL;
    static PyObject *pathstr = NULL;
    static PyObject *pkgstr = NULL;
    PyObject *pkgname, *modname, *modpath, *modules, *parent;
    int orig_level = level;

    if (globals == NULL || !PyDict_Check(globals) || !level)
        goto return_none;

    if (namestr == NULL) {
        namestr = PyUnicode_InternFromString("__name__");
        if (namestr == NULL)
            return NULL;
    }
    if (pathstr == NULL) {
        pathstr = PyUnicode_InternFromString("__path__");
        if (pathstr == NULL)
            return NULL;
    }
    if (pkgstr == NULL) {
        pkgstr = PyUnicode_InternFromString("__package__");
        if (pkgstr == NULL)
            return NULL;
    }

    pkgname = PyDict_GetItem(globals, pkgstr);

    if ((pkgname != NULL) && (pkgname != Py_None)) {
        /* __package__ is set, so use it */
        if (!PyUnicode_Check(pkgname)) {
            PyErr_SetString(PyExc_ValueError,
                            "__package__ set to non-string");
            return NULL;
        }
        if (PyUnicode_GET_LENGTH(pkgname) == 0) {
            if (level > 0) {
                PyErr_SetString(PyExc_ValueError,
                    "Attempted relative import in non-package");
                return NULL;
            }
            goto return_none;
        }
        Py_INCREF(pkgname);
        nameobj = pkgname;
    } else {
        /* __package__ not set, so figure it out and set it */
        modname = PyDict_GetItem(globals, namestr);
        if (modname == NULL || !PyUnicode_Check(modname))
            goto return_none;

        modpath = PyDict_GetItem(globals, pathstr);
        if (modpath != NULL) {
            /* __path__ is set, so modname is already the package name */
            int error;

            error = PyDict_SetItem(globals, pkgstr, modname);
            if (error) {
                PyErr_SetString(PyExc_ValueError,
                                "Could not set __package__");
                return NULL;
            }
            Py_INCREF(modname);
            nameobj = modname;
        } else {
            /* Normal module, so work out the package name if any */
            Py_ssize_t len;
            len = PyUnicode_FindChar(modname, '.',
                                     0, PyUnicode_GET_LENGTH(modname), -1);
            if (len == -2)
                return NULL;
            if (len < 0) {
                if (level > 0) {
                    PyErr_SetString(PyExc_ValueError,
                        "Attempted relative import in non-package");
                    return NULL;
                }
                if (PyDict_SetItem(globals, pkgstr, Py_None)) {
                    PyErr_SetString(PyExc_ValueError,
                        "Could not set __package__");
                    return NULL;
                }
                goto return_none;
            }
            pkgname = PyUnicode_Substring(modname, 0, len);
            if (pkgname == NULL)
                return NULL;
            if (PyDict_SetItem(globals, pkgstr, pkgname)) {
                Py_DECREF(pkgname);
                PyErr_SetString(PyExc_ValueError,
                                "Could not set __package__");
                return NULL;
            }
            nameobj = pkgname;
        }
    }
    if (level > 1) {
        Py_ssize_t dot, end = PyUnicode_GET_LENGTH(nameobj);
        PyObject *newname;
        while (--level > 0) {
            dot = PyUnicode_FindChar(nameobj, '.', 0, end, -1);
            if (dot == -2) {
                Py_DECREF(nameobj);
                return NULL;
            }
            if (dot < 0) {
                Py_DECREF(nameobj);
                PyErr_SetString(PyExc_ValueError,
                    "Attempted relative import beyond "
                    "toplevel package");
                return NULL;
            }
            end = dot;
        }
        newname = PyUnicode_Substring(nameobj, 0, end);
        Py_DECREF(nameobj);
        if (newname == NULL)
            return NULL;
        nameobj = newname;
    }

    modules = PyImport_GetModuleDict();
    parent = PyDict_GetItem(modules, nameobj);
    if (parent == NULL) {
        int err;

        if (orig_level >= 1) {
            PyErr_Format(PyExc_SystemError,
                "Parent module %R not loaded, "
                "cannot perform relative import", nameobj);
            Py_DECREF(nameobj);
            return NULL;
        }

        err = PyErr_WarnFormat(
            PyExc_RuntimeWarning, 1,
            "Parent module %R not found while handling absolute import",
            nameobj);
        Py_DECREF(nameobj);
        if (err)
            return NULL;

        goto return_none;
    }
    *p_name = nameobj;
    return parent;
    /* We expect, but can't guarantee, if parent != None, that:
       - parent.__name__ == name
       - parent.__dict__ is globals
       If this is violated...  Who cares? */

return_none:
    nameobj = PyUnicode_New(0, 0);
    if (nameobj == NULL)
        return NULL;
    *p_name = nameobj;
    return Py_None;
}

/* altmod is either None or same as mod */
static PyObject *
load_next(PyObject *mod, PyObject *altmod,
          PyObject *inputname, PyObject **p_outputname,
          Py_UCS4 *buf, Py_ssize_t *p_buflen, Py_ssize_t bufsize)
{
    Py_UCS4 *dot;
    Py_ssize_t len;
    Py_UCS4 *p;
    PyObject *fullname, *name, *result, *mark_name;
    const Py_UCS4 *nameuni;

    *p_outputname = NULL;

    if (PyUnicode_GET_LENGTH(inputname) == 0) {
        /* completely empty module name should only happen in
           'from . import' (or '__import__("")')*/
        Py_INCREF(mod);
        return mod;
    }

    nameuni = PyUnicode_AsUCS4Copy(inputname);
    if (nameuni == NULL)
        return NULL;

    dot = Py_UCS4_strchr(nameuni, '.');
    if (dot != NULL) {
        len = dot - nameuni;
        if (len == 0) {
            PyErr_SetString(PyExc_ValueError,
                            "Empty module name");
            return NULL;
        }
    }
    else
        len = PyUnicode_GET_LENGTH(inputname);

    if (*p_buflen+len+1 >= bufsize) {
        PyErr_SetString(PyExc_ValueError,
                        "Module name too long");
        return NULL;
    }

    p = buf + *p_buflen;
    if (p != buf) {
        *p++ = '.';
        *p_buflen += 1;
    }
    Py_UCS4_strncpy(p, nameuni, len);
    p[len] = '\0';
    *p_buflen += len;

    fullname = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                         buf, *p_buflen);
    if (fullname == NULL)
        return NULL;
    name = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                     p, len);
    if (name == NULL) {
        Py_DECREF(fullname);
        return NULL;
    }
    result = import_submodule(mod, name, fullname);
    Py_DECREF(fullname);
    if (result == Py_None && altmod != mod) {
        Py_DECREF(result);
        /* Here, altmod must be None and mod must not be None */
        result = import_submodule(altmod, name, name);
        Py_DECREF(name);
        if (result != NULL && result != Py_None) {
            mark_name = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                                  buf, *p_buflen);
            if (mark_name == NULL) {
                Py_DECREF(result);
                return NULL;
            }
            if (mark_miss(mark_name) != 0) {
                Py_DECREF(result);
                Py_DECREF(mark_name);
                return NULL;
            }
            Py_DECREF(mark_name);
            Py_UCS4_strncpy(buf, nameuni, len);
            buf[len] = '\0';
            *p_buflen = len;
        }
    }
    else
        Py_DECREF(name);
    if (result == NULL)
        return NULL;

    if (result == Py_None) {
        Py_DECREF(result);
        PyErr_Format(PyExc_ImportError,
                     "No module named %R", inputname);
        return NULL;
    }

    if (dot != NULL) {
        *p_outputname = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                                  dot+1, Py_UCS4_strlen(dot+1));
        if (*p_outputname == NULL) {
            Py_DECREF(result);
            return NULL;
        }
    }

    return result;
}

static int
mark_miss(PyObject *name)
{
    PyObject *modules = PyImport_GetModuleDict();
    return PyDict_SetItem(modules, name, Py_None);
}

static int
ensure_fromlist(PyObject *mod, PyObject *fromlist, PyObject *name,
                int recursive)
{
    int i;
    PyObject *fullname;
    Py_ssize_t fromlist_len;

    if (!PyObject_HasAttrString(mod, "__path__"))
        return 1;

    fromlist_len = PySequence_Size(fromlist);

    for (i = 0; i < fromlist_len; i++) {
        PyObject *item = PySequence_GetItem(fromlist, i);
        int hasit;
        if (item == NULL)
            return 0;
        if (!PyUnicode_Check(item)) {
            PyErr_SetString(PyExc_TypeError,
                            "Item in ``from list'' not a string");
            Py_DECREF(item);
            return 0;
        }
        if (PyUnicode_READ_CHAR(item, 0) == '*') {
            PyObject *all;
            Py_DECREF(item);
            /* See if the package defines __all__ */
            if (recursive)
                continue; /* Avoid endless recursion */
            all = PyObject_GetAttrString(mod, "__all__");
            if (all == NULL)
                PyErr_Clear();
            else {
                int ret = ensure_fromlist(mod, all, name, 1);
                Py_DECREF(all);
                if (!ret)
                    return 0;
            }
            continue;
        }
        hasit = PyObject_HasAttr(mod, item);
        if (!hasit) {
            PyObject *submod;
            fullname = PyUnicode_FromFormat("%U.%U", name, item);
            if (fullname != NULL) {
                submod = import_submodule(mod, item, fullname);
                Py_DECREF(fullname);
            }
            else
                submod = NULL;
            Py_XDECREF(submod);
            if (submod == NULL) {
                Py_DECREF(item);
                return 0;
            }
        }
        Py_DECREF(item);
    }

    return 1;
}

static int
add_submodule(PyObject *mod, PyObject *submod, PyObject *fullname,
              PyObject *subname, PyObject *modules)
{
    if (mod == Py_None)
        return 1;
    /* Irrespective of the success of this load, make a
       reference to it in the parent package module.  A copy gets
       saved in the modules dictionary under the full name, so get a
       reference from there, if need be.  (The exception is when the
       load failed with a SyntaxError -- then there's no trace in
       sys.modules.  In that case, of course, do nothing extra.) */
    if (submod == NULL) {
        submod = PyDict_GetItem(modules, fullname);
        if (submod == NULL)
            return 1;
    }
    if (PyModule_Check(mod)) {
        /* We can't use setattr here since it can give a
         * spurious warning if the submodule name shadows a
         * builtin name */
        PyObject *dict = PyModule_GetDict(mod);
        if (!dict)
            return 0;
        if (PyDict_SetItem(dict, subname, submod) < 0)
            return 0;
    }
    else {
        if (PyObject_SetAttr(mod, subname, submod) < 0)
            return 0;
    }
    return 1;
}

static PyObject *
import_submodule(PyObject *mod, PyObject *subname, PyObject *fullname)
{
    PyObject *modules = PyImport_GetModuleDict();
    PyObject *m = NULL, *bufobj, *path_list, *loader;
    struct filedescr *fdp;
    FILE *fp;

    /* Require:
       if mod == None: subname == fullname
       else: mod.__name__ + "." + subname == fullname
    */

    if ((m = PyDict_GetItem(modules, fullname)) != NULL) {
        Py_INCREF(m);
        return m;
    }

    if (mod == Py_None)
        path_list = NULL;
    else {
        path_list = PyObject_GetAttrString(mod, "__path__");
        if (path_list == NULL) {
            PyErr_Clear();
            Py_INCREF(Py_None);
            return Py_None;
        }
    }

    fdp = find_module(fullname, subname, path_list,
                      &bufobj, &fp, &loader);
    Py_XDECREF(path_list);
    if (fdp == NULL) {
        if (!PyErr_ExceptionMatches(PyExc_ImportError))
            return NULL;
        PyErr_Clear();
        Py_INCREF(Py_None);
        return Py_None;
    }
    m = load_module(fullname, fp, bufobj, fdp->type, loader);
    Py_XDECREF(bufobj);
    Py_XDECREF(loader);
    if (fp)
        fclose(fp);
    if (m == NULL)
        return NULL;
    if (!add_submodule(mod, m, fullname, subname, modules)) {
        Py_XDECREF(m);
        return NULL;
    }
    return m;
}


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

PyObject *
PyImport_ReloadModule(PyObject *m)
{
    PyInterpreterState *interp = PyThreadState_Get()->interp;
    PyObject *modules_reloading = interp->modules_reloading;
    PyObject *modules = PyImport_GetModuleDict();
    PyObject *path_list = NULL, *loader = NULL, *existing_m = NULL;
    PyObject *nameobj, *bufobj, *subnameobj;
    Py_UCS4 *name = NULL, *subname;
    struct filedescr *fdp;
    FILE *fp = NULL;
    PyObject *newm = NULL;

    if (modules_reloading == NULL) {
        Py_FatalError("PyImport_ReloadModule: "
                      "no modules_reloading dictionary!");
        return NULL;
    }

    if (m == NULL || !PyModule_Check(m)) {
        PyErr_SetString(PyExc_TypeError,
                        "reload() argument must be module");
        return NULL;
    }
    nameobj = PyModule_GetNameObject(m);
    if (nameobj == NULL || PyUnicode_READY(nameobj) == -1)
        return NULL;
    if (m != PyDict_GetItem(modules, nameobj)) {
        PyErr_Format(PyExc_ImportError,
                     "reload(): module %R not in sys.modules",
                     nameobj);
        Py_DECREF(nameobj);
        return NULL;
    }
    existing_m = PyDict_GetItem(modules_reloading, nameobj);
    if (existing_m != NULL) {
        /* Due to a recursive reload, this module is already
           being reloaded. */
        Py_DECREF(nameobj);
        Py_INCREF(existing_m);
        return existing_m;
    }
    if (PyDict_SetItem(modules_reloading, nameobj, m) < 0) {
        Py_DECREF(nameobj);
        return NULL;
    }

    name = PyUnicode_AsUCS4Copy(nameobj);
    if (!name) {
        Py_DECREF(nameobj);
        return NULL;
    }
    subname = Py_UCS4_strrchr(name, '.');
    if (subname == NULL) {
        Py_INCREF(nameobj);
        subnameobj = nameobj;
    }
    else {
        PyObject *parentname, *parent;
        Py_ssize_t len;
        len = subname - name;
        parentname = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                               name, len);
        if (parentname == NULL) {
            goto error;
        }
        parent = PyDict_GetItem(modules, parentname);
        if (parent == NULL) {
            PyErr_Format(PyExc_ImportError,
                "reload(): parent %R not in sys.modules",
                 parentname);
            Py_DECREF(parentname);
            goto error;
        }
        Py_DECREF(parentname);
        path_list = PyObject_GetAttrString(parent, "__path__");
        if (path_list == NULL)
            PyErr_Clear();
        subname++;
        len = PyUnicode_GET_LENGTH(nameobj) - (len + 1);
        subnameobj = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
                                               subname, len);
    }
    if (subnameobj == NULL)
        goto error;
    fdp = find_module(nameobj, subnameobj, path_list,
                      &bufobj, &fp, &loader);
    Py_DECREF(subnameobj);
    Py_XDECREF(path_list);

    if (fdp == NULL) {
        Py_XDECREF(loader);
        goto error;
    }

    newm = load_module(nameobj, fp, bufobj, fdp->type, loader);
    Py_XDECREF(bufobj);
    Py_XDECREF(loader);

    if (fp)
        fclose(fp);
    if (newm == NULL) {
        /* load_module probably removed name from modules because of
         * the error.  Put back the original module object.  We're
         * going to return NULL in this case regardless of whether
         * replacing name succeeds, so the return value is ignored.
         */
        PyDict_SetItem(modules, nameobj, m);
    }

error:
    imp_modules_reloading_clear();
    Py_DECREF(nameobj);
    PyMem_Free(name);
    return newm;
}


/* 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;
}


/* Module 'imp' provides Python access to the primitives used for
   importing modules.
*/

static PyObject *
imp_make_magic(long magic)
{
    char buf[4];

    buf[0] = (char) ((magic >>  0) & 0xff);
    buf[1] = (char) ((magic >>  8) & 0xff);
    buf[2] = (char) ((magic >> 16) & 0xff);
    buf[3] = (char) ((magic >> 24) & 0xff);

    return PyBytes_FromStringAndSize(buf, 4);
}

static PyObject *
imp_get_magic(PyObject *self, PyObject *noargs)
{
    return imp_make_magic(pyc_magic);
}

static PyObject *
imp_get_tag(PyObject *self, PyObject *noargs)
{
    return PyUnicode_FromString(pyc_tag);
}

static PyObject *
imp_get_suffixes(PyObject *self, PyObject *noargs)
{
    PyObject *list;
    struct filedescr *fdp;

    list = PyList_New(0);
    if (list == NULL)
        return NULL;
    for (fdp = _PyImport_Filetab; fdp->suffix != NULL; fdp++) {
        PyObject *item = Py_BuildValue("ssi",
                               fdp->suffix, fdp->mode, fdp->type);
        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);
    }
    return list;
}

static PyObject *
call_find_module(PyObject *name, PyObject *path_list)
{
    extern int fclose(FILE *);
    PyObject *fob, *ret;
    PyObject *pathobj;
    struct filedescr *fdp;
    FILE *fp;
    int fd = -1;
    char *found_encoding = NULL;
    char *encoding = NULL;

    if (path_list == Py_None)
        path_list = NULL;
    fdp = find_module(NULL, name, path_list,
                      &pathobj, &fp, NULL);
    if (fdp == NULL)
        return NULL;
    if (fp != NULL) {
        fd = fileno(fp);
        if (fd != -1)
            fd = dup(fd);
        fclose(fp);
        if (fd == -1) {
            PyErr_SetFromErrno(PyExc_OSError);
            return NULL;
        }
        fp = NULL;
    }
    if (fd != -1) {
        if (strchr(fdp->mode, 'b') == NULL) {
            /* PyTokenizer_FindEncodingFilename() returns PyMem_MALLOC'ed
               memory. */
            found_encoding = PyTokenizer_FindEncodingFilename(fd, pathobj);
            lseek(fd, 0, 0); /* Reset position */
            if (found_encoding == NULL && PyErr_Occurred()) {
                Py_XDECREF(pathobj);
                return NULL;
            }
            encoding = (found_encoding != NULL) ? found_encoding :
                   (char*)PyUnicode_GetDefaultEncoding();
        }
        fob = PyFile_FromFd(fd, NULL, fdp->mode, -1,
                            (char*)encoding, NULL, NULL, 1);
        if (fob == NULL) {
            Py_XDECREF(pathobj);
            close(fd);
            PyMem_FREE(found_encoding);
            return NULL;
        }
    }
    else {
        fob = Py_None;
        Py_INCREF(fob);
    }
    if (pathobj == NULL) {
        Py_INCREF(Py_None);
        pathobj = Py_None;
    }
    ret = Py_BuildValue("NN(ssi)",
                  fob, pathobj, fdp->suffix, fdp->mode, fdp->type);
    PyMem_FREE(found_encoding);

    return ret;
}

static PyObject *
imp_find_module(PyObject *self, PyObject *args)
{
    PyObject *name, *path_list = NULL;
    if (!PyArg_ParseTuple(args, "U|O:find_module",
                          &name, &path_list))
        return NULL;
    return call_find_module(name, path_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));
}

static FILE *
get_file(PyObject *pathname, PyObject *fob, char *mode)
{
    FILE *fp;
    if (mode[0] == 'U')
        mode = "r" PY_STDIOTEXTMODE;
    if (fob == NULL) {
        fp = _Py_fopen(pathname, mode);
    }
    else {
        int fd = PyObject_AsFileDescriptor(fob);
        if (fd == -1)
            return NULL;
        if (!_PyVerify_fd(fd))
            goto error;
        /* the FILE struct gets a new fd, so that it can be closed
         * independently of the file descriptor given
         */
        fd = dup(fd);
        if (fd == -1)
            goto error;
        fp = fdopen(fd, mode);
    }
    if (fp)
        return fp;
error:
    PyErr_SetFromErrno(PyExc_IOError);
    return NULL;
}

static PyObject *
imp_load_compiled(PyObject *self, PyObject *args)
{
    PyObject *name, *pathname;
    PyObject *fob = NULL;
    PyObject *m;
    FILE *fp;
    if (!PyArg_ParseTuple(args, "UO&|O:load_compiled",
                          &name,
                          PyUnicode_FSDecoder, &pathname,
                          &fob))
        return NULL;
    fp = get_file(pathname, fob, "rb");
    if (fp == NULL) {
        Py_DECREF(pathname);
        return NULL;
    }
    m = load_compiled_module(name, pathname, fp);
    fclose(fp);
    Py_DECREF(pathname);
    return m;
}

#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 = get_file(NULL, fob, "r");
        if (fp == NULL) {
            Py_DECREF(pathname);
            return NULL;
        }
    }
    else
        fp = NULL;
    mod = _PyImport_LoadDynamicModule(name, pathname, fp);
    Py_DECREF(pathname);
    if (fp)
        fclose(fp);
    return mod;
}

#endif /* HAVE_DYNAMIC_LOADING */

static PyObject *
imp_load_source(PyObject *self, PyObject *args)
{
    PyObject *name, *pathname;
    PyObject *fob = NULL;
    PyObject *m;
    FILE *fp;
    if (!PyArg_ParseTuple(args, "UO&|O:load_source",
                          &name,
                          PyUnicode_FSDecoder, &pathname,
                          &fob))
        return NULL;
    fp = get_file(pathname, fob, "r");
    if (fp == NULL) {
        Py_DECREF(pathname);
        return NULL;
    }
    m = load_source_module(name, pathname, fp);
    Py_DECREF(pathname);
    fclose(fp);
    return m;
}

static PyObject *
imp_load_module(PyObject *self, PyObject *args)
{
    PyObject *name, *fob, *pathname, *pathname_obj, *ret;
    char *suffix; /* Unused */
    char *mode;
    int type;
    FILE *fp;

    if (!PyArg_ParseTuple(args, "UOO(ssi):load_module",
                          &name, &fob, &pathname_obj, &suffix, &mode, &type))
        return NULL;
    if (pathname_obj != Py_None) {
        if (!PyUnicode_FSDecoder(pathname_obj, &pathname))
            return NULL;
    }
    else
        pathname = NULL;

    if (*mode) {
        /* Mode must start with 'r' or 'U' and must not contain '+'.
           Implicit in this test is the assumption that the mode
           may contain other modifiers like 'b' or 't'. */

        if (!(*mode == 'r' || *mode == 'U') || strchr(mode, '+')) {
            PyErr_Format(PyExc_ValueError,
                         "invalid file open mode %.200s", mode);
            Py_XDECREF(pathname);
            return NULL;
        }
    }
    if (fob == Py_None)
        fp = NULL;
    else {
        fp = get_file(NULL, fob, mode);
        if (fp == NULL) {
            Py_XDECREF(pathname);
            return NULL;
        }
    }
    ret = load_module(name, fp, pathname, type, NULL);
    Py_XDECREF(pathname);
    if (fp)
        fclose(fp);
    return ret;
}

static PyObject *
imp_load_package(PyObject *self, PyObject *args)
{
    PyObject *name, *pathname;
    PyObject * ret;
    if (!PyArg_ParseTuple(args, "UO&:load_package",
                          &name, PyUnicode_FSDecoder, &pathname))
        return NULL;
    ret = load_package(name, pathname);
    Py_DECREF(pathname);
    return ret;
}

static PyObject *
imp_new_module(PyObject *self, PyObject *args)
{
    PyObject *name;
    if (!PyArg_ParseTuple(args, "U:new_module", &name))
        return NULL;
    return PyModule_NewObject(name);
}

static PyObject *
imp_reload(PyObject *self, PyObject *v)
{
    return PyImport_ReloadModule(v);
}

PyDoc_STRVAR(doc_reload,
"reload(module) -> module\n\
\n\
Reload the module.  The module must have been successfully imported before.");

static PyObject *
imp_cache_from_source(PyObject *self, PyObject *args, PyObject *kws)
{
    static char *kwlist[] = {"path", "debug_override", NULL};

    PyObject *pathname, *cpathname;
    PyObject *debug_override = NULL;
    int debug = !Py_OptimizeFlag;

    if (!PyArg_ParseTupleAndKeywords(
                args, kws, "O&|O", kwlist,
                PyUnicode_FSDecoder, &pathname, &debug_override))
        return NULL;

    if (debug_override != NULL &&
        (debug = PyObject_IsTrue(debug_override)) < 0) {
        Py_DECREF(pathname);
        return NULL;
    }

    cpathname = make_compiled_pathname(pathname, debug);
    Py_DECREF(pathname);

    if (cpathname == NULL) {
        PyErr_Format(PyExc_SystemError, "path buffer too short");
        return NULL;
    }
    return cpathname;
}

PyDoc_STRVAR(doc_cache_from_source,
"Given the path to a .py file, return the path to its .pyc/.pyo file.\n\
\n\
The .py file does not need to exist; this simply returns the path to the\n\
.pyc/.pyo file calculated as if the .py file were imported.  The extension\n\
will be .pyc unless __debug__ is not defined, then it will be .pyo.\n\
\n\
If debug_override is not None, then it must be a boolean and is taken as\n\
the value of __debug__ instead.");

static PyObject *
imp_source_from_cache(PyObject *self, PyObject *args, PyObject *kws)
{
    static char *kwlist[] = {"path", NULL};
    PyObject *pathname, *source;

    if (!PyArg_ParseTupleAndKeywords(
                args, kws, "O&", kwlist,
                PyUnicode_FSDecoder, &pathname))
        return NULL;

    source = make_source_pathname(pathname);
    if (source == NULL) {
        PyErr_Format(PyExc_ValueError, "Not a PEP 3147 pyc path: %R",
                     pathname);
        Py_DECREF(pathname);
        return NULL;
    }
    Py_DECREF(pathname);
    return source;
}

PyDoc_STRVAR(doc_source_from_cache,
"Given the path to a .pyc./.pyo file, return the path to its .py file.\n\
\n\
The .pyc/.pyo file does not need to exist; this simply returns the path to\n\
the .py file calculated to correspond to the .pyc/.pyo file.  If path\n\
does not conform to PEP 3147 format, ValueError will be raised.");

/* Doc strings */

PyDoc_STRVAR(doc_imp,
"This module provides the components needed to build your own\n\
__import__ function.  Undocumented functions are obsolete.");

PyDoc_STRVAR(doc_find_module,
"find_module(name, [path]) -> (file, filename, (suffix, mode, type))\n\
Search for a module.  If path is omitted or None, search for a\n\
built-in, frozen or special module and continue search in sys.path.\n\
The module name cannot contain '.'; to search for a submodule of a\n\
package, pass the submodule name and the package's __path__.");

PyDoc_STRVAR(doc_load_module,
"load_module(name, file, filename, (suffix, mode, type)) -> module\n\
Load a module, given information returned by find_module().\n\
The module name must include the full package name, if any.");

PyDoc_STRVAR(doc_get_magic,
"get_magic() -> string\n\
Return the magic number for .pyc or .pyo files.");

PyDoc_STRVAR(doc_get_tag,
"get_tag() -> string\n\
Return the magic tag for .pyc or .pyo files.");

PyDoc_STRVAR(doc_get_suffixes,
"get_suffixes() -> [(suffix, mode, type), ...]\n\
Return a list of (suffix, mode, type) tuples describing the files\n\
that find_module() looks for.");

PyDoc_STRVAR(doc_new_module,
"new_module(name) -> module\n\
Create a new module.  Do not enter it in sys.modules.\n\
The module name must include the full package name, if any.");

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[] = {
    {"find_module",      imp_find_module,  METH_VARARGS, doc_find_module},
    {"get_magic",        imp_get_magic,    METH_NOARGS,  doc_get_magic},
    {"get_tag",          imp_get_tag,      METH_NOARGS,  doc_get_tag},
    {"get_suffixes", imp_get_suffixes, METH_NOARGS,  doc_get_suffixes},
    {"load_module",      imp_load_module,  METH_VARARGS, doc_load_module},
    {"new_module",       imp_new_module,   METH_VARARGS, doc_new_module},
    {"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},
    {"reload",       imp_reload,       METH_O,       doc_reload},
    {"cache_from_source", (PyCFunction)imp_cache_from_source,
     METH_VARARGS | METH_KEYWORDS, doc_cache_from_source},
    {"source_from_cache", (PyCFunction)imp_source_from_cache,
     METH_VARARGS | METH_KEYWORDS, doc_source_from_cache},
    /* The rest are obsolete */
    {"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},
    {"load_compiled",           imp_load_compiled,      METH_VARARGS},
#ifdef HAVE_DYNAMIC_LOADING
    {"load_dynamic",            imp_load_dynamic,       METH_VARARGS},
#endif
    {"load_package",            imp_load_package,       METH_VARARGS},
    {"load_source",             imp_load_source,        METH_VARARGS},
    {"_fix_co_filename",        imp_fix_co_filename,    METH_VARARGS},
    {NULL,                      NULL}           /* sentinel */
};

static int
setint(PyObject *d, char *name, int value)
{
    PyObject *v;
    int err;

    v = PyLong_FromLong((long)value);
    err = PyDict_SetItemString(d, name, v);
    Py_XDECREF(v);
    return err;
}

typedef struct {
    PyObject_HEAD
} NullImporter;

static int
NullImporter_init(NullImporter *self, PyObject *args, PyObject *kwds)
{
#ifndef MS_WINDOWS
    PyObject *path;
    struct stat statbuf;
    int rv;

    if (!_PyArg_NoKeywords("NullImporter()", kwds))
        return -1;

    if (!PyArg_ParseTuple(args, "O&:NullImporter",
                          PyUnicode_FSConverter, &path))
        return -1;

    if (PyBytes_GET_SIZE(path) == 0) {
        Py_DECREF(path);
        PyErr_SetString(PyExc_ImportError, "empty pathname");
        return -1;
    }

    rv = stat(PyBytes_AS_STRING(path), &statbuf);
    Py_DECREF(path);
    if (rv == 0) {
        /* it exists */
        if (S_ISDIR(statbuf.st_mode)) {
            /* it's a directory */
            PyErr_SetString(PyExc_ImportError, "existing directory");
            return -1;
        }
    }
#else /* MS_WINDOWS */
    PyObject *pathobj;
    DWORD rv;
    wchar_t *path;

    if (!_PyArg_NoKeywords("NullImporter()", kwds))
        return -1;

    if (!PyArg_ParseTuple(args, "U:NullImporter",
                          &pathobj))
        return -1;

    if (PyUnicode_GET_LENGTH(pathobj) == 0) {
        PyErr_SetString(PyExc_ImportError, "empty pathname");
        return -1;
    }

    path = PyUnicode_AsWideCharString(pathobj, NULL);
    if (path == NULL)
        return -1;
    /* see issue1293 and issue3677:
     * stat() on Windows doesn't recognise paths like
     * "e:\\shared\\" and "\\\\whiterab-c2znlh\\shared" as dirs.
     */
    rv = GetFileAttributesW(path);
    PyMem_Free(path);
    if (rv != INVALID_FILE_ATTRIBUTES) {
        /* it exists */
        if (rv & FILE_ATTRIBUTE_DIRECTORY) {
            /* it's a directory */
            PyErr_SetString(PyExc_ImportError, "existing directory");
            return -1;
        }
    }
#endif
    return 0;
}

static PyObject *
NullImporter_find_module(NullImporter *self, PyObject *args)
{
    Py_RETURN_NONE;
}

static PyMethodDef NullImporter_methods[] = {
    {"find_module", (PyCFunction)NullImporter_find_module, METH_VARARGS,
     "Always return None"
    },
    {NULL}  /* Sentinel */
};


PyTypeObject PyNullImporter_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "imp.NullImporter",        /*tp_name*/
    sizeof(NullImporter),      /*tp_basicsize*/
    0,                         /*tp_itemsize*/
    0,                         /*tp_dealloc*/
    0,                         /*tp_print*/
    0,                         /*tp_getattr*/
    0,                         /*tp_setattr*/
    0,                         /*tp_reserved*/
    0,                         /*tp_repr*/
    0,                         /*tp_as_number*/
    0,                         /*tp_as_sequence*/
    0,                         /*tp_as_mapping*/
    0,                         /*tp_hash */
    0,                         /*tp_call*/
    0,                         /*tp_str*/
    0,                         /*tp_getattro*/
    0,                         /*tp_setattro*/
    0,                         /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT,        /*tp_flags*/
    "Null importer object",    /* tp_doc */
    0,                             /* tp_traverse */
    0,                             /* tp_clear */
    0,                             /* tp_richcompare */
    0,                             /* tp_weaklistoffset */
    0,                             /* tp_iter */
    0,                             /* tp_iternext */
    NullImporter_methods,      /* tp_methods */
    0,                         /* tp_members */
    0,                         /* tp_getset */
    0,                         /* tp_base */
    0,                         /* tp_dict */
    0,                         /* tp_descr_get */
    0,                         /* tp_descr_set */
    0,                         /* tp_dictoffset */
    (initproc)NullImporter_init,      /* tp_init */
    0,                         /* tp_alloc */
    PyType_GenericNew          /* tp_new */
};

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;

    if (PyType_Ready(&PyNullImporter_Type) < 0)
        return NULL;

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

    if (setint(d, "SEARCH_ERROR", SEARCH_ERROR) < 0) goto failure;
    if (setint(d, "PY_SOURCE", PY_SOURCE) < 0) goto failure;
    if (setint(d, "PY_COMPILED", PY_COMPILED) < 0) goto failure;
    if (setint(d, "C_EXTENSION", C_EXTENSION) < 0) goto failure;
    if (setint(d, "PY_RESOURCE", PY_RESOURCE) < 0) goto failure;
    if (setint(d, "PKG_DIRECTORY", PKG_DIRECTORY) < 0) goto failure;
    if (setint(d, "C_BUILTIN", C_BUILTIN) < 0) goto failure;
    if (setint(d, "PY_FROZEN", PY_FROZEN) < 0) goto failure;
    if (setint(d, "PY_CODERESOURCE", PY_CODERESOURCE) < 0) goto failure;
    if (setint(d, "IMP_HOOK", IMP_HOOK) < 0) goto failure;

    Py_INCREF(&PyNullImporter_Type);
    PyModule_AddObject(m, "NullImporter", (PyObject *)&PyNullImporter_Type);
    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