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
       Python 3.3a0  3200 (__qualname__ added)
                     3210 (added size modulo 2**32 to the pyc header)
       Python 3.3a1  3220 (changed PEP 380 implementation)
*/

/* 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 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 (3220 | ((long)'\r'<<16) | ((long)'\n'<<24))
#define TAG "cpython-" MAJOR MINOR;
#define CACHEDIR "__pycache__"
/* Current magic word and string tag as globals. */
static long pyc_magic = MAGIC;
static const char *pyc_tag = TAG;
#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;
    int err = 0;

    if (PyType_Ready(&PyNullImporter_Type) < 0)
        goto error;

    /* adding sys.path_hooks and sys.path_importer_cache */
    v = PyList_New(0);
    if (v == NULL)
        goto error;
    err = PySys_SetObject("meta_path", v);
    Py_DECREF(v);
    if (err)
        goto error;
    v = PyDict_New();
    if (v == NULL)
        goto error;
    err = PySys_SetObject("path_importer_cache", v);
    Py_DECREF(v);
    if (err)
        goto error;
    path_hooks = PyList_New(0);
    if (path_hooks == NULL)
        goto error;
    err = PySys_SetObject("path_hooks", path_hooks);
    if (err) {
  error:
    PyErr_Print();
    Py_FatalError("initializing sys.meta_path, sys.path_hooks, "
                  "path_importer_cache, or NullImporter failed"
                  );
    }
    Py_DECREF(path_hooks);
}

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

    path_hooks = PySys_GetObject("path_hooks");
    if (path_hooks == NULL)
        goto error;

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

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

    return;

  error:
    PyErr_Print();
    Py_FatalError("initializing zipimport or NullImporter failed");
}

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

#ifdef WITH_THREAD

#include "pythread.h"

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

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

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

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);

/* 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 rightmost_sep, but operate on unicode objects. */
static Py_ssize_t
rightmost_sep_obj(PyObject* o, Py_ssize_t start, Py_ssize_t end)
{
    Py_ssize_t found, i;
    Py_UCS4 c;
    for (found = -1, i = start; i < end; i++) {
        c = PyUnicode_READ_CHAR(o, i);
        if (c == SEP
#ifdef ALTSEP
            || c == ALTSEP
#endif
            )
        {
            found = i;
        }
    }
    return found;
}


/* 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 *path)
{
    Py_ssize_t left, right, dot0, dot1, len;
    Py_ssize_t i, j;
    PyObject *result;
    int kind;
    void *data;

    len = PyUnicode_GET_LENGTH(path);
    if (len > MAXPATHLEN)
        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_obj(path, 0, len);
    if (right == -1)
        return NULL;
    left = rightmost_sep_obj(path, 0, right);
    if (left == -1)
        left = 0;
    else
        left++;
    if (right-left !=  sizeof(CACHEDIR)-1)
        return NULL;
    for (i = 0; i < sizeof(CACHEDIR)-1; i++)
        if (PyUnicode_READ_CHAR(path, left+i) != CACHEDIR[i])
            return NULL;

    /* Now verify that the path component to the right of the last slash
       has two dots in it.
    */
    dot0 = PyUnicode_FindChar(path, '.', right+1, len, 1);
    if (dot0 < 0)
        return NULL;
    dot1 = PyUnicode_FindChar(path, '.', dot0+1, len, 1);
    if (dot1 < 0)
        return NULL;
    /* Too many dots? */
    if (PyUnicode_FindChar(path, '.', dot1+1, len, 1) != -1)
        return NULL;

    /* 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.
    */
    result = PyUnicode_New(left + (dot0-right) + 2,
                           PyUnicode_MAX_CHAR_VALUE(path));
    if (!result)
        return NULL;
    kind = PyUnicode_KIND(result);
    data = PyUnicode_DATA(result);
    PyUnicode_CopyCharacters(result, 0, path, 0, (i = left));
    PyUnicode_CopyCharacters(result, left, path, right+1,
                             (j = dot0-right));
    PyUnicode_WRITE(kind, data, i+j,   'p');
    PyUnicode_WRITE(kind, data, i+j+1, 'y');
    assert(_PyUnicode_CheckConsistency(result, 1));
    return result;
}


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;
}


/* 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;
    int err;

    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;

    err = _Py_stat(py, &statbuf);
    if (err == -2)
        goto error;
    if (err == 0 && S_ISREG(statbuf.st_mode)) {
        PyMem_Free(fileuni);
        return py;
    }
    Py_DECREF(py);
    goto unchanged;

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

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


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

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


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

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

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

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

    importer = PyDict_GetItem(path_importer_cache, p);
    if (importer != NULL)
        return importer;

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

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

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

PyAPI_FUNC(PyObject *)
PyImport_GetImporter(PyObject *path) {
    PyObject *importer=NULL, *path_importer_cache=NULL, *path_hooks=NULL;

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


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


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

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

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

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

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


/* Frozen modules */

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

    if (name == NULL)
        return NULL;

    for (p = PyImport_FrozenModules; ; p++) {
        if (p->name == NULL)
            return NULL;
        if (PyUnicode_CompareWithASCIIString(name, p->name) == 0)
            break;
    }
    return p;
}

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

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

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

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

    size = p->size;

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


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

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

    p = find_frozen(name);

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

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


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

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

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

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


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

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

    if (given_fromlist == NULL) {
        fromlist = PyList_New(0);
        if (fromlist == NULL) {
            goto error;
        }
    }
    else {
        fromlist = given_fromlist;
        Py_INCREF(fromlist);
    }
    if (name == NULL) {
        PyErr_SetString(PyExc_ValueError, "Empty module name");
        goto error;
    }

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

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

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

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

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

        for (level_up = 1; level_up < level; level_up += 1) {
            last_dot = PyUnicode_FindChar(package, '.', 0, last_dot, -1);
            if (last_dot == -2) {
                goto error;
            }
            else if (last_dot == -1) {
                PyErr_SetString(PyExc_ValueError,
                                "attempted relative import beyond top-level "
                                "package");
                goto error;
            }
        }
        base = PyUnicode_Substring(package, 0, last_dot);
        if (PyUnicode_GET_LENGTH(name) > 0) {
            PyObject *borrowed_dot, *seq = NULL;

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

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

#ifdef WITH_THREAD
    _PyImport_AcquireLock();
#endif
   /* From this point forward, goto error_with_unlock! */
    if (PyDict_Check(globals)) {
        builtins_import = _PyDict_GetItemId(globals, &PyId___import__);
    }
    if (builtins_import == NULL) {
        builtins_import = _PyDict_GetItemId(interp->builtins, &PyId___import__);
        if (builtins_import == NULL) {
            Py_FatalError("__import__ missing");
        }
    }
    Py_INCREF(builtins_import);

    mod = PyDict_GetItem(interp->modules, abs_name);
    if (mod == Py_None) {
        PyObject *msg = PyUnicode_FromFormat("import of %R halted; "
                                             "None in sys.modules", abs_name);
        if (msg != NULL) {
            PyErr_SetImportError(msg, abs_name, NULL);
            Py_DECREF(msg);
        }
        mod = NULL;
        goto error_with_unlock;
    }
    else if (mod != NULL) {
        Py_INCREF(mod);
    }
    else {
        mod = _PyObject_CallMethodObjIdArgs(interp->importlib,
                                            &PyId__find_and_load, abs_name,
                                            builtins_import, NULL);
        if (mod == NULL) {
            goto error_with_unlock;
        }
    }

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

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

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

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

            if (level == 0) {
                final_mod = PyDict_GetItem(interp->modules, front);
                Py_DECREF(front);
                if (final_mod == NULL) {
                    PyErr_Format(PyExc_KeyError,
                                 "%R not in sys.modules as expected", front);
                }
                else {
                    Py_INCREF(final_mod);
                }
            }
            else {
                Py_ssize_t cut_off = PyUnicode_GET_LENGTH(name) -
                                        PyUnicode_GET_LENGTH(front);
                Py_ssize_t abs_name_len = PyUnicode_GET_LENGTH(abs_name);
                PyObject *to_return = PyUnicode_Substring(abs_name, 0,
                                                        abs_name_len - cut_off);
                Py_DECREF(front);
                if (to_return == NULL) {
                    goto error_with_unlock;
                }

                final_mod = PyDict_GetItem(interp->modules, to_return);
                Py_DECREF(to_return);
                if (final_mod == NULL) {
                    PyErr_Format(PyExc_KeyError,
                                 "%R not in sys.modules as expected",
                                 to_return);
                }
                else {
                    Py_INCREF(final_mod);
                }
            }
        }
        else {
            final_mod = mod;
            Py_INCREF(mod);
        }
    }
    else {
        final_mod = _PyObject_CallMethodObjIdArgs(interp->importlib,
                                                  &PyId__handle_fromlist, mod,
                                                  fromlist, builtins_import,
                                                  NULL);
    }
  error_with_unlock:
#ifdef WITH_THREAD
    if (_PyImport_ReleaseLock() < 0) {
        PyErr_SetString(PyExc_RuntimeError, "not holding the import lock");
    }
#endif
  error:
    Py_XDECREF(abs_name);
    Py_XDECREF(builtins_import);
    Py_XDECREF(mod);
    Py_XDECREF(package);
    Py_XDECREF(globals);
    Py_XDECREF(fromlist);
    return final_mod;
}

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


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

PyObject *
PyImport_ReloadModule(PyObject *m)
{
    PyInterpreterState *interp = PyThreadState_Get()->interp;
    PyObject *modules_reloading = interp->modules_reloading;
    PyObject *modules = PyImport_GetModuleDict();
    PyObject *loader = NULL, *existing_m = NULL;
    PyObject *name;
    Py_ssize_t subname_start;
    PyObject *newm = NULL;
    _Py_IDENTIFIER(__loader__);
    _Py_IDENTIFIER(load_module);

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

    subname_start = PyUnicode_FindChar(name, '.', 0,
                                       PyUnicode_GET_LENGTH(name), -1);
    if (subname_start != -1) {
        PyObject *parentname, *parent;
        parentname = PyUnicode_Substring(name, 0, subname_start);
        if (parentname == NULL) {
            goto error;
        }
        parent = PyDict_GetItem(modules, parentname);
        Py_XDECREF(parent);
        if (parent == NULL) {
            PyErr_Format(PyExc_ImportError,
                "reload(): parent %R not in sys.modules",
                 parentname);
            goto error;
        }
    }

    loader = _PyObject_GetAttrId(m, &PyId___loader__);
    if (loader == NULL) {
        goto error;
    }
    newm = _PyObject_CallMethodId(loader, &PyId_load_module, "O", name);
    Py_DECREF(loader);
    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, name, m);
    }

error:
    imp_modules_reloading_clear();
    Py_DECREF(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 *
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);
        if (!fp) {
            if (!PyErr_Occurred())
                PyErr_SetFromErrno(PyExc_IOError);
            return NULL;
        }
        return fp;
    }
    else {
        int fd = PyObject_AsFileDescriptor(fob);
        if (fd == -1)
            return NULL;
        if (!_PyVerify_fd(fd)) {
            PyErr_SetFromErrno(PyExc_IOError);
            return NULL;
        }

        /* 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) {
            PyErr_SetFromErrno(PyExc_IOError);
            return NULL;
        }

        fp = fdopen(fd, mode);
        if (!fp) {
            PyErr_SetFromErrno(PyExc_IOError);
            return NULL;
        }
        return fp;
    }
}

#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_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.");


/* Doc strings */

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

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_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[] = {
    {"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},
    {"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},
    {"get_frozen_object",       imp_get_frozen_object,  METH_VARARGS},
    {"is_frozen_package",   imp_is_frozen_package,  METH_VARARGS},
    {"init_builtin",            imp_init_builtin,       METH_VARARGS},
    {"init_frozen",             imp_init_frozen,        METH_VARARGS},
    {"is_builtin",              imp_is_builtin,         METH_VARARGS},
    {"is_frozen",               imp_is_frozen,          METH_VARARGS},
#ifdef HAVE_DYNAMIC_LOADING
    {"load_dynamic",            imp_load_dynamic,       METH_VARARGS},
#endif
    {"_fix_co_filename",        imp_fix_co_filename,    METH_VARARGS},
    {NULL,                      NULL}           /* sentinel */
};

static 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