Patch by Jeremy Katz (SF #1609407)

[python.git] / Python / import.c

/* Module definition and import implementation */

#include "Python.h"

#include "Python-ast.h"
#include "pyarena.h"
#include "pythonrun.h"
#include "errcode.h"
#include "marshal.h"
#include "code.h"
#include "compile.h"
#include "eval.h"
#include "osdefs.h"
#include "importdl.h"

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

extern time_t PyOS_GetLastModificationTime(char *, FILE *);
                                                /* In getmtime.c */

/* 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 atleast 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.

   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: 62141 (peephole optimizations)
.
*/
#define MAGIC (62141 | ((long)'\r'<<16) | ((long)'\n'<<24))

/* Magic word as global; note that _PyImport_Init() can change the
   value of this global to accommodate for alterations of how the
   compiler works which are enabled by command line switches. */
static long pyc_magic = MAGIC;

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

/* 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;

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

static PyTypeObject NullImporterType;   /* Forward reference */

/* Initialize things */

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

        /* prepare _PyImport_Filetab: copy entries from
           _PyImport_DynLoadFiletab and _PyImport_StandardFiletab.
         */
        for (scan = _PyImport_DynLoadFiletab; scan->suffix != NULL; ++scan)
                ++countD;
        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.");
        memcpy(filetab, _PyImport_DynLoadFiletab,
               countD * sizeof(struct filedescr));
        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++) {
#ifndef RISCOS
                        if (strcmp(filetab->suffix, ".pyc") == 0)
                                filetab->suffix = ".pyo";
#else
                        if (strcmp(filetab->suffix, "/pyc") == 0)
                                filetab->suffix = "/pyo";
#endif
                }
        }

        if (Py_UnicodeFlag) {
                /* Fix the pyc_magic so that byte compiled code created
                   using the all-Unicode method doesn't interfere with
                   code created in normal operation mode. */
                pyc_magic = MAGIC + 1;
        }
}

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(&NullImporterType) < 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;

static void
lock_import(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;
}

static int
unlock_import(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. */

void
_PyImport_ReInitLock(void)
{
#ifdef _AIX
        if (import_lock != NULL)
                import_lock = PyThread_allocate_lock();
#endif
}

#else

#define lock_import()
#define unlock_import() 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
        lock_import();
#endif
        Py_INCREF(Py_None);
        return Py_None;
}

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

/* 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", "exitfunc",
        "exc_type", "exc_value", "exc_traceback",
        "last_type", "last_value", "last_traceback",
        "path_hooks", "path_importer_cache", "meta_path",
        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;
        char *name;
        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, "__builtin__");
        if (value != NULL && PyModule_Check(value)) {
                dict = PyModule_GetDict(value);
                if (Py_VerboseFlag)
                        PySys_WriteStderr("# clear __builtin__._\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 __builtin__ 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 __builtin__
           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 __builtin__ and sys) and delete them */
        do {
                ndone = 0;
                pos = 0;
                while (PyDict_Next(modules, &pos, &key, &value)) {
                        if (value->ob_refcnt != 1)
                                continue;
                        if (PyString_Check(key) && PyModule_Check(value)) {
                                name = PyString_AS_STRING(key);
                                if (strcmp(name, "__builtin__") == 0)
                                        continue;
                                if (strcmp(name, "sys") == 0)
                                        continue;
                                if (Py_VerboseFlag)
                                        PySys_WriteStderr(
                                                "# cleanup[1] %s\n", name);
                                _PyModule_Clear(value);
                                PyDict_SetItem(modules, key, Py_None);
                                ndone++;
                        }
                }
        } while (ndone > 0);

        /* Next, delete all modules (still skipping __builtin__ and sys) */
        pos = 0;
        while (PyDict_Next(modules, &pos, &key, &value)) {
                if (PyString_Check(key) && PyModule_Check(value)) {
                        name = PyString_AS_STRING(key);
                        if (strcmp(name, "__builtin__") == 0)
                                continue;
                        if (strcmp(name, "sys") == 0)
                                continue;
                        if (Py_VerboseFlag)
                                PySys_WriteStderr("# cleanup[2] %s\n", name);
                        _PyModule_Clear(value);
                        PyDict_SetItem(modules, key, Py_None);
                }
        }

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

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


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

long
PyImport_GetMagicNumber(void)
{
        return pyc_magic;
}


/* 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_FixupExtension()
   immediately after the module initialization function succeeds.  A
   copy can be retrieved from there by calling
   _PyImport_FindExtension(). */

PyObject *
_PyImport_FixupExtension(char *name, char *filename)
{
        PyObject *modules, *mod, *dict, *copy;
        if (extensions == NULL) {
                extensions = PyDict_New();
                if (extensions == NULL)
                        return NULL;
        }
        modules = PyImport_GetModuleDict();
        mod = PyDict_GetItemString(modules, name);
        if (mod == NULL || !PyModule_Check(mod)) {
                PyErr_Format(PyExc_SystemError,
                  "_PyImport_FixupExtension: module %.200s not loaded", name);
                return NULL;
        }
        dict = PyModule_GetDict(mod);
        if (dict == NULL)
                return NULL;
        copy = PyDict_Copy(dict);
        if (copy == NULL)
                return NULL;
        PyDict_SetItemString(extensions, filename, copy);
        Py_DECREF(copy);
        return copy;
}

PyObject *
_PyImport_FindExtension(char *name, char *filename)
{
        PyObject *dict, *mod, *mdict;
        if (extensions == NULL)
                return NULL;
        dict = PyDict_GetItemString(extensions, filename);
        if (dict == NULL)
                return NULL;
        mod = PyImport_AddModule(name);
        if (mod == NULL)
                return NULL;
        mdict = PyModule_GetDict(mod);
        if (mdict == NULL)
                return NULL;
        if (PyDict_Update(mdict, dict))
                return NULL;
        if (Py_VerboseFlag)
                PySys_WriteStderr("import %s # previously loaded (%s)\n",
                        name, filename);
        return mod;
}


/* 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_AddModule(const char *name)
{
        PyObject *modules = PyImport_GetModuleDict();
        PyObject *m;

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

        return m;
}

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

/* Execute a code object in a module and return the module object
 * WITH INCREMENTED REFERENCE COUNT.  If an error occurs, name is
 * removed from sys.modules, to avoid leaving damaged module objects
 * in sys.modules.  The caller may wish to restore the original
 * module object (if any) in this case; PyImport_ReloadModule is an
 * example.
 */
PyObject *
PyImport_ExecCodeModule(char *name, PyObject *co)
{
        return PyImport_ExecCodeModuleEx(name, co, (char *)NULL);
}

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

        m = PyImport_AddModule(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 */
        v = NULL;
        if (pathname != NULL) {
                v = PyString_FromString(pathname);
                if (v == NULL)
                        PyErr_Clear();
        }
        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);

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

        if ((m = PyDict_GetItemString(modules, name)) == NULL) {
                PyErr_Format(PyExc_ImportError,
                             "Loaded module %.200s not found in sys.modules",
                             name);
                return NULL;
        }

        Py_INCREF(m);

        return m;

  error:
        _RemoveModule(name);
        return NULL;
}


/* 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. */

static char *
make_compiled_pathname(char *pathname, char *buf, size_t buflen)
{
        size_t len = strlen(pathname);
        if (len+2 > buflen)
                return NULL;

#ifdef MS_WINDOWS
        /* Treat .pyw as if it were .py.  The case of ".pyw" must match
           that used in _PyImport_StandardFiletab. */
        if (len >= 4 && strcmp(&pathname[len-4], ".pyw") == 0)
                --len;  /* pretend 'w' isn't there */
#endif
        memcpy(buf, pathname, len);
        buf[len] = Py_OptimizeFlag ? 'o' : 'c';
        buf[len+1] = '\0';

        return buf;
}


/* 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(char *pathname, time_t mtime, char *cpathname)
{
        FILE *fp;
        long magic;
        long pyc_mtime;

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


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

static PyCodeObject *
read_compiled_module(char *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 %.200s", 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(char *name, char *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 %.200s", cpathname);
                return NULL;
        }
        (void) PyMarshal_ReadLongFromFile(fp);
        co = read_compiled_module(cpathname, fp);
        if (co == NULL)
                return NULL;
        if (Py_VerboseFlag)
                PySys_WriteStderr("import %s # precompiled from %s\n",
                        name, cpathname);
        m = PyImport_ExecCodeModuleEx(name, (PyObject *)co, cpathname);
        Py_DECREF(co);

        return m;
}

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

static PyCodeObject *
parse_source_module(const char *pathname, FILE *fp)
{
        PyCodeObject *co = NULL;
        mod_ty mod;
        PyArena *arena = PyArena_New();
        if (arena == NULL)
                return NULL;

        mod = PyParser_ASTFromFile(fp, pathname, Py_file_input, 0, 0, 0, 
                                   NULL, arena);
        if (mod) {
                co = PyAST_Compile(mod, pathname, NULL, arena);
        }
        PyArena_Free(arena);
        return co;
}


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

static FILE *
open_exclusive(char *filename)
{
#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
                        , 0666, "ctxt=bin", "shr=nil"
#else
                        , 0666
#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
}


/* 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, char *cpathname, time_t mtime)
{
        FILE *fp;

        fp = open_exclusive(cpathname);
        if (fp == NULL) {
                if (Py_VerboseFlag)
                        PySys_WriteStderr(
                                "# can't create %s\n", cpathname);
                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_WriteStderr("# can't write %s\n", cpathname);
                /* Don't keep partial file */
                fclose(fp);
                (void) unlink(cpathname);
                return;
        }
        /* 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_WriteStderr("# wrote %s\n", cpathname);
}


/* 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(char *name, char *pathname, FILE *fp)
{
        time_t mtime;
        FILE *fpc;
        char buf[MAXPATHLEN+1];
        char *cpathname;
        PyCodeObject *co;
        PyObject *m;

        mtime = PyOS_GetLastModificationTime(pathname, fp);
        if (mtime == (time_t)(-1)) {
                PyErr_Format(PyExc_RuntimeError,
                             "unable to get modification time from '%s'",
                             pathname);
                return NULL;
        }
#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 (mtime >> 32) {
                PyErr_SetString(PyExc_OverflowError,
                        "modification time overflows a 4 byte field");
                return NULL;
        }
#endif
        cpathname = make_compiled_pathname(pathname, buf,
                                           (size_t)MAXPATHLEN + 1);
        if (cpathname != NULL &&
            (fpc = check_compiled_module(pathname, mtime, cpathname))) {
                co = read_compiled_module(cpathname, fpc);
                fclose(fpc);
                if (co == NULL)
                        return NULL;
                if (Py_VerboseFlag)
                        PySys_WriteStderr("import %s # precompiled from %s\n",
                                name, cpathname);
                pathname = cpathname;
        }
        else {
                co = parse_source_module(pathname, fp);
                if (co == NULL)
                        return NULL;
                if (Py_VerboseFlag)
                        PySys_WriteStderr("import %s # from %s\n",
                                name, pathname);
                if (cpathname)
                        write_compiled_module(co, cpathname, mtime);
        }
        m = PyImport_ExecCodeModuleEx(name, (PyObject *)co, pathname);
        Py_DECREF(co);

        return m;
}


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

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

static PyObject *
load_package(char *name, char *pathname)
{
        PyObject *m, *d;
        PyObject *file = NULL;
        PyObject *path = NULL;
        int err;
        char buf[MAXPATHLEN+1];
        FILE *fp = NULL;
        struct filedescr *fdp;

        m = PyImport_AddModule(name);
        if (m == NULL)
                return NULL;
        if (Py_VerboseFlag)
                PySys_WriteStderr("import %s # directory %s\n",
                        name, pathname);
        d = PyModule_GetDict(m);
        file = PyString_FromString(pathname);
        if (file == NULL)
                goto error;
        path = Py_BuildValue("[O]", file);
        if (path == NULL)
                goto error;
        err = PyDict_SetItemString(d, "__file__", file);
        if (err == 0)
                err = PyDict_SetItemString(d, "__path__", path);
        if (err != 0)
                goto error;
        buf[0] = '\0';
        fdp = find_module(name, "__init__", path, buf, sizeof(buf), &fp, NULL);
        if (fdp == NULL) {
                if (PyErr_ExceptionMatches(PyExc_ImportError)) {
                        PyErr_Clear();
                        Py_INCREF(m);
                }
                else
                        m = NULL;
                goto cleanup;
        }
        m = load_module(name, fp, buf, fdp->type, NULL);
        if (fp != NULL)
                fclose(fp);
        goto cleanup;

  error:
        m = NULL;
  cleanup:
        Py_XDECREF(path);
        Py_XDECREF(file);
        return m;
}


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

static int
is_builtin(char *name)
{
        int i;
        for (i = 0; PyImport_Inittab[i].name != NULL; i++) {
                if (strcmp(name, PyImport_Inittab[i].name) == 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 *)&NullImporterType, 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;
}

/* 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(const char *, struct filedescr **,
                                        char *, Py_ssize_t);
#endif

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

static struct filedescr *
find_module(char *fullname, char *subname, PyObject *path, char *buf,
            size_t buflen, FILE **p_fp, PyObject **p_loader)
{
        Py_ssize_t i, npath;
        size_t len, namelen;
        struct filedescr *fdp = NULL;
        char *filemode;
        FILE *fp = NULL;
        PyObject *path_hooks, *path_importer_cache;
#ifndef RISCOS
        struct stat statbuf;
#endif
        static struct filedescr fd_frozen = {"", "", PY_FROZEN};
        static struct filedescr fd_builtin = {"", "", C_BUILTIN};
        static struct filedescr fd_package = {"", "", PKG_DIRECTORY};
        char name[MAXPATHLEN+1];
#if defined(PYOS_OS2)
        size_t saved_len;
        size_t saved_namelen;
        char *saved_buf = NULL;
#endif
        if (p_loader != NULL)
                *p_loader = NULL;

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

        /* 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_ImportError,
                                        "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",
                                                     "sO", fullname,
                                                     path != NULL ?
                                                     path : 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 (path != NULL && PyString_Check(path)) {
                /* The only type of submodule allowed inside a "frozen"
                   package are other frozen modules or packages. */
                if (PyString_Size(path) + 1 + strlen(name) >= (size_t)buflen) {
                        PyErr_SetString(PyExc_ImportError,
                                        "full frozen module name too long");
                        return NULL;
                }
                strcpy(buf, PyString_AsString(path));
                strcat(buf, ".");
                strcat(buf, name);
                strcpy(name, buf);
                if (find_frozen(name) != NULL) {
                        strcpy(buf, name);
                        return &fd_frozen;
                }
                PyErr_Format(PyExc_ImportError,
                             "No frozen submodule named %.200s", name);
                return NULL;
        }
        if (path == NULL) {
                if (is_builtin(name)) {
                        strcpy(buf, name);
                        return &fd_builtin;
                }
                if ((find_frozen(name)) != NULL) {
                        strcpy(buf, name);
                        return &fd_frozen;
                }

#ifdef MS_COREDLL
                fp = PyWin_FindRegisteredModule(name, &fdp, buf, buflen);
                if (fp != NULL) {
                        *p_fp = fp;
                        return fdp;
                }
#endif
                path = PySys_GetObject("path");
        }
        if (path == NULL || !PyList_Check(path)) {
                PyErr_SetString(PyExc_ImportError,
                                "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_ImportError,
                                "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_ImportError,
                                "sys.path_importer_cache must be a dict");
                return NULL;
        }

        npath = PyList_Size(path);
        namelen = strlen(name);
        for (i = 0; i < npath; i++) {
                PyObject *copy = NULL;
                PyObject *v = PyList_GetItem(path, i);
                if (!v)
                        return NULL;
#ifdef Py_USING_UNICODE
                if (PyUnicode_Check(v)) {
                        copy = PyUnicode_Encode(PyUnicode_AS_UNICODE(v),
                                PyUnicode_GET_SIZE(v), Py_FileSystemDefaultEncoding, NULL);
                        if (copy == NULL)
                                return NULL;
                        v = copy;
                }
                else
#endif
                if (!PyString_Check(v))
                        continue;
                len = PyString_GET_SIZE(v);
                if (len + 2 + namelen + MAXSUFFIXSIZE >= buflen) {
                        Py_XDECREF(copy);
                        continue; /* Too long */
                }
                strcpy(buf, PyString_AS_STRING(v));
                if (strlen(buf) != len) {
                        Py_XDECREF(copy);
                        continue; /* v contains '\0' */
                }

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

                        importer = get_path_importer(path_importer_cache,
                                                     path_hooks, v);
                        if (importer == NULL) {
                                Py_XDECREF(copy);
                                return NULL;
                        }
                        /* Note: importer is a borrowed reference */
                        if (importer != Py_None) {
                                PyObject *loader;
                                loader = PyObject_CallMethod(importer,
                                                             "find_module",
                                                             "s", fullname);
                                Py_XDECREF(copy);
                                if (loader == NULL)
                                        return NULL;  /* error */
                                if (loader != Py_None) {
                                        /* a loader was found */
                                        *p_loader = loader;
                                        return &importhookdescr;
                                }
                                Py_DECREF(loader);
                                continue;
                        }
                }
                /* no hook was found, use builtin import */

                if (len > 0 && buf[len-1] != SEP
#ifdef ALTSEP
                    && buf[len-1] != ALTSEP
#endif
                    )
                        buf[len++] = SEP;
                strcpy(buf+len, name);
                len += namelen;

                /* Check for package import (buf holds a directory name,
                   and there's an __init__ module in that directory */
#ifdef HAVE_STAT
                if (stat(buf, &statbuf) == 0 &&         /* it exists */
                    S_ISDIR(statbuf.st_mode) &&         /* it's a directory */
                    case_ok(buf, len, namelen, name)) { /* case matches */
                        if (find_init_module(buf)) { /* and has __init__.py */
                                Py_XDECREF(copy);
                                return &fd_package;
                        }
                        else {
                                char warnstr[MAXPATHLEN+80];
                                sprintf(warnstr, "Not importing directory "
                                        "'%.*s': missing __init__.py", 
                                        MAXPATHLEN, buf);
                                if (PyErr_Warn(PyExc_ImportWarning,
                                               warnstr)) {
                                        Py_XDECREF(copy);
                                        return NULL;
                                }
                        }
                }
#else
                /* XXX How are you going to test for directories? */
#ifdef RISCOS
                if (isdir(buf) &&
                    case_ok(buf, len, namelen, name)) {
                        if (find_init_module(buf)) {
                                Py_XDECREF(copy);
                                return &fd_package;
                        }
                        else {
                                char warnstr[MAXPATHLEN+80];
                                sprintf(warnstr, "Not importing directory "
                                        "'%.*s': missing __init__.py", 
                                        MAXPATHLEN, buf);
                                if (PyErr_Warn(PyExc_ImportWarning,
                                               warnstr)) {
                                        Py_XDECREF(copy);
                                        return NULL;
                                }
                }
#endif
#endif
#if defined(PYOS_OS2)
                /* take a snapshot of the module spec for restoration
                 * after the 8 character DLL hackery
                 */
                saved_buf = strdup(buf);
                saved_len = len;
                saved_namelen = namelen;
#endif /* PYOS_OS2 */
                for (fdp = _PyImport_Filetab; fdp->suffix != NULL; fdp++) {
#if defined(PYOS_OS2)
                        /* OS/2 limits DLLs to 8 character names (w/o
                           extension)
                         * so if the name is longer than that and its a
                         * dynamically loaded module we're going to try,
                         * truncate the name before trying
                         */
                        if (strlen(subname) > 8) {
                                /* is this an attempt to load a C extension? */
                                const struct filedescr *scan;
                                scan = _PyImport_DynLoadFiletab;
                                while (scan->suffix != NULL) {
                                        if (!strcmp(scan->suffix, fdp->suffix))
                                                break;
                                        else
                                                scan++;
                                }
                                if (scan->suffix != NULL) {
                                        /* yes, so truncate the name */
                                        namelen = 8;
                                        len -= strlen(subname) - namelen;
                                        buf[len] = '\0';
                                }
                        }
#endif /* PYOS_OS2 */
                        strcpy(buf+len, fdp->suffix);
                        if (Py_VerboseFlag > 1)
                                PySys_WriteStderr("# trying %s\n", buf);
                        filemode = fdp->mode;
                        if (filemode[0] == 'U')
                                filemode = "r" PY_STDIOTEXTMODE;
                        fp = fopen(buf, filemode);
                        if (fp != NULL) {
                                if (case_ok(buf, len, namelen, name))
                                        break;
                                else {   /* continue search */
                                        fclose(fp);
                                        fp = NULL;
                                }
                        }
#if defined(PYOS_OS2)
                        /* restore the saved snapshot */
                        strcpy(buf, saved_buf);
                        len = saved_len;
                        namelen = saved_namelen;
#endif
                }
#if defined(PYOS_OS2)
                /* don't need/want the module name snapshot anymore */
                if (saved_buf)
                {
                        free(saved_buf);
                        saved_buf = NULL;
                }
#endif
                Py_XDECREF(copy);
                if (fp != NULL)
                        break;
        }
        if (fp == NULL) {
                PyErr_Format(PyExc_ImportError,
                             "No module named %.200s", name);
                return NULL;
        }
        *p_fp = fp;
        return fdp;
}

/* Helpers for main.c
 *  Find the source file corresponding to a named module
 */
struct filedescr *
_PyImport_FindModule(const char *name, PyObject *path, char *buf,
            size_t buflen, FILE **p_fp, PyObject **p_loader)
{
        return find_module((char *) name, (char *) name, path,
                           buf, buflen, p_fp, p_loader);
}

PyAPI_FUNC(int) _PyImport_IsScript(struct filedescr * fd)
{
        return fd->type == PY_SOURCE || fd->type == PY_COMPILED;
}

/* case_ok(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_ok() is to return 1 if there's a case-sensitive match for
 * name, else 0.  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.
 */

/* 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_ok().
 */
#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>

#elif defined(RISCOS)
#include "oslib/osfscontrol.h"
#endif

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

/* MS_WINDOWS */
#if defined(MS_WINDOWS)
        WIN32_FIND_DATA data;
        HANDLE h;

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

        h = FindFirstFile(buf, &data);
        if (h == INVALID_HANDLE_VALUE) {
                PyErr_Format(PyExc_NameError,
                  "Can't find file for module %.100s\n(filename %.300s)",
                  name, buf);
                return 0;
        }
        FindClose(h);
        return strncmp(data.cFileName, name, namelen) == 0;

/* DJGPP */
#elif 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 0;
        }
        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 */

/* RISC OS */
#elif defined(RISCOS)
        char canon[MAXPATHLEN+1]; /* buffer for the canonical form of the path */
        char buf2[MAXPATHLEN+2];
        char *nameWithExt = buf+len-namelen;
        int canonlen;
        os_error *e;

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

        /* workaround:
           append wildcard, otherwise case of filename wouldn't be touched */
        strcpy(buf2, buf);
        strcat(buf2, "*");

        e = xosfscontrol_canonicalise_path(buf2,canon,0,0,MAXPATHLEN+1,&canonlen);
        canonlen = MAXPATHLEN+1-canonlen;
        if (e || canonlen<=0 || canonlen>(MAXPATHLEN+1) )
                return 0;
        if (strcmp(nameWithExt, canon+canonlen-strlen(nameWithExt))==0)
                return 1; /* match */

        return 0;

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

        if (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
        return 1;

#endif
}


#ifdef HAVE_STAT
/* Helper to look for __init__.py or __init__.py[co] in potential package */
static int
find_init_module(char *buf)
{
        const size_t save_len = strlen(buf);
        size_t i = save_len;
        char *pname;  /* pointer to start of __init__ */
        struct stat statbuf;

/*      For calling case_ok(buf, len, namelen, name):
 *      /a/b/c/d/e/f/g/h/i/j/k/some_long_module_name.py\0
 *      ^                      ^                   ^    ^
 *      |--------------------- buf ---------------------|
 *      |------------------- len ------------------|
 *                             |------ name -------|
 *                             |----- namelen -----|
 */
        if (save_len + 13 >= MAXPATHLEN)
                return 0;
        buf[i++] = SEP;
        pname = buf + i;
        strcpy(pname, "__init__.py");
        if (stat(buf, &statbuf) == 0) {
                if (case_ok(buf,
                            save_len + 9,       /* len("/__init__") */
                            8,                  /* len("__init__") */
                            pname)) {
                        buf[save_len] = '\0';
                        return 1;
                }
        }
        i += strlen(pname);
        strcpy(buf+i, Py_OptimizeFlag ? "o" : "c");
        if (stat(buf, &statbuf) == 0) {
                if (case_ok(buf,
                            save_len + 9,       /* len("/__init__") */
                            8,                  /* len("__init__") */
                            pname)) {
                        buf[save_len] = '\0';
                        return 1;
                }
        }
        buf[save_len] = '\0';
        return 0;
}

#else

#ifdef RISCOS
static int
find_init_module(buf)
        char *buf;
{
        int save_len = strlen(buf);
        int i = save_len;

        if (save_len + 13 >= MAXPATHLEN)
                return 0;
        buf[i++] = SEP;
        strcpy(buf+i, "__init__/py");
        if (isfile(buf)) {
                buf[save_len] = '\0';
                return 1;
        }

        if (Py_OptimizeFlag)
                strcpy(buf+i, "o");
        else
                strcpy(buf+i, "c");
        if (isfile(buf)) {
                buf[save_len] = '\0';
                return 1;
        }
        buf[save_len] = '\0';
        return 0;
}
#endif /*RISCOS*/

#endif /* HAVE_STAT */


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

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

static PyObject *
load_module(char *name, FILE *fp, char *buf, int type, PyObject *loader)
{
        PyObject *modules;
        PyObject *m;
        int err;

        /* 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, buf, fp);
                break;

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

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

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

        case C_BUILTIN:
        case PY_FROZEN:
                if (buf != NULL && buf[0] != '\0')
                        name = buf;
                if (type == C_BUILTIN)
                        err = init_builtin(name);
                else
                        err = PyImport_ImportFrozenModule(name);
                if (err < 0)
                        return NULL;
                if (err == 0) {
                        PyErr_Format(PyExc_ImportError,
                                     "Purported %s module %.200s not found",
                                     type == C_BUILTIN ?
                                                "builtin" : "frozen",
                                     name);
                        return NULL;
                }
                modules = PyImport_GetModuleDict();
                m = PyDict_GetItemString(modules, name);
                if (m == NULL) {
                        PyErr_Format(
                                PyExc_ImportError,
                                "%s module %.200s not properly initialized",
                                type == C_BUILTIN ?
                                        "builtin" : "frozen",
                                name);
                        return NULL;
                }
                Py_INCREF(m);
                break;

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

        default:
                PyErr_Format(PyExc_ImportError,
                             "Don't know how to import %.200s (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(char *name)
{
        struct _inittab *p;

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

        for (p = PyImport_Inittab; p->name != NULL; p++) {
                if (strcmp(name, p->name) == 0) {
                        if (p->initfunc == NULL) {
                                PyErr_Format(PyExc_ImportError,
                                    "Cannot re-init internal module %.200s",
                                    name);
                                return -1;
                        }
                        if (Py_VerboseFlag)
                                PySys_WriteStderr("import %s # builtin\n", name);
                        (*p->initfunc)();
                        if (PyErr_Occurred())
                                return -1;
                        if (_PyImport_FixupExtension(name, name) == NULL)
                                return -1;
                        return 1;
                }
        }
        return 0;
}


/* Frozen modules */

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

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

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

        if (p == NULL) {
                PyErr_Format(PyExc_ImportError,
                             "No such frozen object named %.200s",
                             name);
                return NULL;
        }
        if (p->code == NULL) {
                PyErr_Format(PyExc_ImportError,
                             "Excluded frozen object named %.200s",
                             name);
                return NULL;
        }
        size = p->size;
        if (size < 0)
                size = -size;
        return PyMarshal_ReadObjectFromString((char *)p->code, size);
}

/* Initialize a frozen module.
   Return 1 for succes, 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_ImportFrozenModule(char *name)
{
        struct _frozen *p = find_frozen(name);
        PyObject *co;
        PyObject *m;
        int ispackage;
        int size;

        if (p == NULL)
                return 0;
        if (p->code == NULL) {
                PyErr_Format(PyExc_ImportError,
                             "Excluded frozen object named %.200s",
                             name);
                return -1;
        }
        size = p->size;
        ispackage = (size < 0);
        if (ispackage)
                size = -size;
        if (Py_VerboseFlag)
                PySys_WriteStderr("import %s # 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 %.200s is not a code object",
                             name);
                goto err_return;
        }
        if (ispackage) {
                /* Set __path__ to the package name */
                PyObject *d, *s;
                int err;
                m = PyImport_AddModule(name);
                if (m == NULL)
                        goto err_return;
                d = PyModule_GetDict(m);
                s = PyString_InternFromString(name);
                if (s == NULL)
                        goto err_return;
                err = PyDict_SetItemString(d, "__path__", s);
                Py_DECREF(s);
                if (err != 0)
                        goto err_return;
        }
        m = PyImport_ExecCodeModuleEx(name, co, "<frozen>");
        if (m == NULL)
                goto err_return;
        Py_DECREF(co);
        Py_DECREF(m);
        return 1;
err_return:
        Py_DECREF(co);
        return -1;
}


/* 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 = PyString_FromString(name);
        if (pname == NULL)
                return NULL;
        result = PyImport_Import(pname);
        Py_DECREF(pname);
        return result;
}

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

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

static PyObject *
import_module_level(char *name, PyObject *globals, PyObject *locals,
                    PyObject *fromlist, int level)
{
        char buf[MAXPATHLEN+1];
        Py_ssize_t buflen = 0;
        PyObject *parent, *head, *next, *tail;

        parent = get_parent(globals, buf, &buflen, level);
        if (parent == NULL)
                return NULL;

        head = load_next(parent, Py_None, &name, buf, &buflen);
        if (head == NULL)
                return NULL;

        tail = head;
        Py_INCREF(tail);
        while (name) {
                next = load_next(tail, tail, &name, buf, &buflen);
                Py_DECREF(tail);
                if (next == NULL) {
                        Py_DECREF(head);
                        return NULL;
                }
                tail = next;
        }
        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);
        if (!ensure_fromlist(tail, fromlist, buf, buflen, 0)) {
                Py_DECREF(tail);
                return NULL;
        }

        return tail;
}

/* For DLL compatibility */
#undef PyImport_ImportModuleEx
PyObject *
PyImport_ImportModuleEx(char *name, PyObject *globals, PyObject *locals,
                        PyObject *fromlist)
{
        PyObject *result;
        lock_import();
        result = import_module_level(name, globals, locals, fromlist, -1);
        if (unlock_import() < 0) {
                Py_XDECREF(result);
                PyErr_SetString(PyExc_RuntimeError,
                                "not holding the import lock");
                return NULL;
        }
        return result;
}
#define PyImport_ImportModuleEx(n, g, l, f) \
        PyImport_ImportModuleLevel(n, g, l, f, -1);

PyObject *
PyImport_ImportModuleLevel(char *name, PyObject *globals, PyObject *locals,
                         PyObject *fromlist, int level)
{
        PyObject *result;
        lock_import();
        result = import_module_level(name, globals, locals, fromlist, level);
        if (unlock_import() < 0) {
                Py_XDECREF(result);
                PyErr_SetString(PyExc_RuntimeError,
                                "not holding the import lock");
                return NULL;
        }
        return result;
}

/* 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 buf, with the length of
   the name in *p_buflen.

   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, char *buf, Py_ssize_t *p_buflen, int level)
{
        static PyObject *namestr = NULL;
        static PyObject *pathstr = NULL;
        PyObject *modname, *modpath, *modules, *parent;

        if (globals == NULL || !PyDict_Check(globals) || !level)
                return Py_None;

        if (namestr == NULL) {
                namestr = PyString_InternFromString("__name__");
                if (namestr == NULL)
                        return NULL;
        }
        if (pathstr == NULL) {
                pathstr = PyString_InternFromString("__path__");
                if (pathstr == NULL)
                        return NULL;
        }

        *buf = '\0';
        *p_buflen = 0;
        modname = PyDict_GetItem(globals, namestr);
        if (modname == NULL || !PyString_Check(modname))
                return Py_None;

        modpath = PyDict_GetItem(globals, pathstr);
        if (modpath != NULL) {
                Py_ssize_t len = PyString_GET_SIZE(modname);
                if (len > MAXPATHLEN) {
                        PyErr_SetString(PyExc_ValueError,
                                        "Module name too long");
                        return NULL;
                }
                strcpy(buf, PyString_AS_STRING(modname));
        }
        else {
                char *start = PyString_AS_STRING(modname);
                char *lastdot = strrchr(start, '.');
                size_t len;
                if (lastdot == NULL && level > 0) {
                        PyErr_SetString(PyExc_ValueError,
                                "Attempted relative import in non-package");
                        return NULL;
                }
                if (lastdot == NULL)
                        return Py_None;
                len = lastdot - start;
                if (len >= MAXPATHLEN) {
                        PyErr_SetString(PyExc_ValueError,
                                        "Module name too long");
                        return NULL;
                }
                strncpy(buf, start, len);
                buf[len] = '\0';
        }

        while (--level > 0) {
                char *dot = strrchr(buf, '.');
                if (dot == NULL) {
                        PyErr_SetString(PyExc_ValueError,
                                "Attempted relative import beyond "
                                "toplevel package");
                        return NULL;
                }
                *dot = '\0';
        }
        *p_buflen = strlen(buf);

        modules = PyImport_GetModuleDict();
        parent = PyDict_GetItemString(modules, buf);
        if (parent == NULL)
                PyErr_Format(PyExc_SystemError,
                                "Parent module '%.200s' not loaded", buf);
        return parent;
        /* We expect, but can't guarantee, if parent != None, that:
           - parent.__name__ == buf
           - parent.__dict__ is globals
           If this is violated...  Who cares? */
}

/* altmod is either None or same as mod */
static PyObject *
load_next(PyObject *mod, PyObject *altmod, char **p_name, char *buf,
          Py_ssize_t *p_buflen)
{
        char *name = *p_name;
        char *dot = strchr(name, '.');
        size_t len;
        char *p;
        PyObject *result;

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

        if (dot == NULL) {
                *p_name = NULL;
                len = strlen(name);
        }
        else {
                *p_name = dot+1;
                len = dot-name;
        }
        if (len == 0) {
                PyErr_SetString(PyExc_ValueError,
                                "Empty module name");
                return NULL;
        }

        p = buf + *p_buflen;
        if (p != buf)
                *p++ = '.';
        if (p+len-buf >= MAXPATHLEN) {
                PyErr_SetString(PyExc_ValueError,
                                "Module name too long");
                return NULL;
        }
        strncpy(p, name, len);
        p[len] = '\0';
        *p_buflen = p+len-buf;

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

        if (result == Py_None) {
                Py_DECREF(result);
                PyErr_Format(PyExc_ImportError,
                             "No module named %.200s", name);
                return NULL;
        }

        return result;
}

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

static int
ensure_fromlist(PyObject *mod, PyObject *fromlist, char *buf, Py_ssize_t buflen,
                int recursive)
{
        int i;

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

        for (i = 0; ; i++) {
                PyObject *item = PySequence_GetItem(fromlist, i);
                int hasit;
                if (item == NULL) {
                        if (PyErr_ExceptionMatches(PyExc_IndexError)) {
                                PyErr_Clear();
                                return 1;
                        }
                        return 0;
                }
                if (!PyString_Check(item)) {
                        PyErr_SetString(PyExc_TypeError,
                                        "Item in ``from list'' not a string");
                        Py_DECREF(item);
                        return 0;
                }
                if (PyString_AS_STRING(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, buf, buflen, 1);
                                Py_DECREF(all);
                                if (!ret)
                                        return 0;
                        }
                        continue;
                }
                hasit = PyObject_HasAttr(mod, item);
                if (!hasit) {
                        char *subname = PyString_AS_STRING(item);
                        PyObject *submod;
                        char *p;
                        if (buflen + strlen(subname) >= MAXPATHLEN) {
                                PyErr_SetString(PyExc_ValueError,
                                                "Module name too long");
                                Py_DECREF(item);
                                return 0;
                        }
                        p = buf + buflen;
                        *p++ = '.';
                        strcpy(p, subname);
                        submod = import_submodule(mod, subname, buf);
                        Py_XDECREF(submod);
                        if (submod == NULL) {
                                Py_DECREF(item);
                                return 0;
                        }
                }
                Py_DECREF(item);
        }

        /* NOTREACHED */
}

static int
add_submodule(PyObject *mod, PyObject *submod, char *fullname, char *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_GetItemString(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_SetItemString(dict, subname, submod) < 0)
                        return 0;
        }
        else {
                if (PyObject_SetAttrString(mod, subname, submod) < 0)
                        return 0;
        }
        return 1;
}

static PyObject *
import_submodule(PyObject *mod, char *subname, char *fullname)
{
        PyObject *modules = PyImport_GetModuleDict();
        PyObject *m = NULL;

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

        if ((m = PyDict_GetItemString(modules, fullname)) != NULL) {
                Py_INCREF(m);
        }
        else {
                PyObject *path, *loader = NULL;
                char buf[MAXPATHLEN+1];
                struct filedescr *fdp;
                FILE *fp = NULL;

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

                buf[0] = '\0';
                fdp = find_module(fullname, subname, path, buf, MAXPATHLEN+1,
                                  &fp, &loader);
                Py_XDECREF(path);
                if (fdp == NULL) {
                        if (!PyErr_ExceptionMatches(PyExc_ImportError))
                                return NULL;
                        PyErr_Clear();
                        Py_INCREF(Py_None);
                        return Py_None;
                }
                m = load_module(fullname, fp, buf, fdp->type, loader);
                Py_XDECREF(loader);
                if (fp)
                        fclose(fp);
                if (!add_submodule(mod, m, fullname, subname, modules)) {
                        Py_XDECREF(m);
                        m = NULL;
                }
        }

        return m;
}


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

PyObject *
PyImport_ReloadModule(PyObject *m)
{
        PyObject *modules = PyImport_GetModuleDict();
        PyObject *path = NULL, *loader = NULL;
        char *name, *subname;
        char buf[MAXPATHLEN+1];
        struct filedescr *fdp;
        FILE *fp = NULL;
        PyObject *newm;

        if (m == NULL || !PyModule_Check(m)) {
                PyErr_SetString(PyExc_TypeError,
                                "reload() argument must be module");
                return NULL;
        }
        name = PyModule_GetName(m);
        if (name == NULL)
                return NULL;
        if (m != PyDict_GetItemString(modules, name)) {
                PyErr_Format(PyExc_ImportError,
                             "reload(): module %.200s not in sys.modules",
                             name);
                return NULL;
        }
        subname = strrchr(name, '.');
        if (subname == NULL)
                subname = name;
        else {
                PyObject *parentname, *parent;
                parentname = PyString_FromStringAndSize(name, (subname-name));
                if (parentname == NULL)
                        return NULL;
                parent = PyDict_GetItem(modules, parentname);
                if (parent == NULL) {
                        PyErr_Format(PyExc_ImportError,
                            "reload(): parent %.200s not in sys.modules",
                            PyString_AS_STRING(parentname));
                        Py_DECREF(parentname);
                        return NULL;
                }
                Py_DECREF(parentname);
                subname++;
                path = PyObject_GetAttrString(parent, "__path__");
                if (path == NULL)
                        PyErr_Clear();
        }
        buf[0] = '\0';
        fdp = find_module(name, subname, path, buf, MAXPATHLEN+1, &fp, &loader);
        Py_XDECREF(path);

        if (fdp == NULL) {
                Py_XDECREF(loader);
                return NULL;
        }

        newm = load_module(name, fp, buf, fdp->type, loader);
        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_SetItemString(modules, name, m);
        }
        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, e.g. by "rexec".
   A dummy list ["__doc__"] is passed as the 4th argument so that
   e.g. PyImport_Import(PyString_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 *r = NULL;

        /* Initialize constant string objects */
        if (silly_list == NULL) {
                import_str = PyString_InternFromString("__import__");
                if (import_str == NULL)
                        return NULL;
                builtins_str = PyString_InternFromString("__builtins__");
                if (builtins_str == NULL)
                        return NULL;
                silly_list = Py_BuildValue("[s]", "__doc__");
                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 */
                PyErr_Clear();

                builtins = PyImport_ImportModuleLevel("__builtin__",
                                                      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 */
        r = PyObject_CallFunctionObjArgs(import, module_name, globals,
                                         globals, silly_list, NULL);

  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_get_magic(PyObject *self, PyObject *noargs)
{
        char buf[4];

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

        return PyString_FromStringAndSize(buf, 4);
}

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(char *name, PyObject *path)
{
        extern int fclose(FILE *);
        PyObject *fob, *ret;
        struct filedescr *fdp;
        char pathname[MAXPATHLEN+1];
        FILE *fp = NULL;

        pathname[0] = '\0';
        if (path == Py_None)
                path = NULL;
        fdp = find_module(NULL, name, path, pathname, MAXPATHLEN+1, &fp, NULL);
        if (fdp == NULL)
                return NULL;
        if (fp != NULL) {
                fob = PyFile_FromFile(fp, pathname, fdp->mode, fclose);
                if (fob == NULL) {
                        fclose(fp);
                        return NULL;
                }
        }
        else {
                fob = Py_None;
                Py_INCREF(fob);
        }
        ret = Py_BuildValue("Os(ssi)",
                      fob, pathname, fdp->suffix, fdp->mode, fdp->type);
        Py_DECREF(fob);
        return ret;
}

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

static PyObject *
imp_init_builtin(PyObject *self, PyObject *args)
{
        char *name;
        int ret;
        PyObject *m;
        if (!PyArg_ParseTuple(args, "s: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_AddModule(name);
        Py_XINCREF(m);
        return m;
}

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

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

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

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

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

static FILE *
get_file(char *pathname, PyObject *fob, char *mode)
{
        FILE *fp;
        if (fob == NULL) {
                if (mode[0] == 'U')
                        mode = "r" PY_STDIOTEXTMODE;
                fp = fopen(pathname, mode);
                if (fp == NULL)
                        PyErr_SetFromErrno(PyExc_IOError);
        }
        else {
                fp = PyFile_AsFile(fob);
                if (fp == NULL)
                        PyErr_SetString(PyExc_ValueError,
                                        "bad/closed file object");
        }
        return fp;
}

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

#ifdef HAVE_DYNAMIC_LOADING

static PyObject *
imp_load_dynamic(PyObject *self, PyObject *args)
{
        char *name;
        char *pathname;
        PyObject *fob = NULL;
        PyObject *m;
        FILE *fp = NULL;
        if (!PyArg_ParseTuple(args, "ss|O!:load_dynamic", &name, &pathname,
                              &PyFile_Type, &fob))
                return NULL;
        if (fob) {
                fp = get_file(pathname, fob, "r");
                if (fp == NULL)
                        return NULL;
        }
        m = _PyImport_LoadDynamicModule(name, pathname, fp);
        return m;
}

#endif /* HAVE_DYNAMIC_LOADING */

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

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

        if (!PyArg_ParseTuple(args, "sOs(ssi):load_module",
                              &name, &fob, &pathname,
                              &suffix, &mode, &type))
                return 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);
                        return NULL;
                }
        }
        if (fob == Py_None)
                fp = NULL;
        else {
                if (!PyFile_Check(fob)) {
                        PyErr_SetString(PyExc_ValueError,
                                "load_module arg#2 should be a file or None");
                        return NULL;
                }
                fp = get_file(pathname, fob, mode);
                if (fp == NULL)
                        return NULL;
        }
        return load_module(name, fp, pathname, type, NULL);
}

static PyObject *
imp_load_package(PyObject *self, PyObject *args)
{
        char *name;
        char *pathname;
        if (!PyArg_ParseTuple(args, "ss:load_package", &name, &pathname))
                return NULL;
        return load_package(name, pathname);
}

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

/* 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_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_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},
        /* The rest are obsolete */
        {"get_frozen_object",   imp_get_frozen_object,  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},
        {NULL,                  NULL}           /* sentinel */
};

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

        v = PyInt_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)
{
        char *path;

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

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

        if (strlen(path) == 0) {
                PyErr_SetString(PyExc_ImportError, "empty pathname");
                return -1;
        } else {
#ifndef RISCOS
                struct stat statbuf;
                int rv;

                rv = stat(path, &statbuf);
                if (rv == 0) {
                        /* it exists */
                        if (S_ISDIR(statbuf.st_mode)) {
                                /* it's a directory */
                                PyErr_SetString(PyExc_ImportError,
                                                "existing directory");
                                return -1;
                        }
                }
#else
                if (object_exists(path)) {
                        /* it exists */
                        if (isdir(path)) {
                                /* 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 */
};


static PyTypeObject NullImporterType = {
        PyObject_HEAD_INIT(NULL)
        0,                         /*ob_size*/
        "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_compare*/
        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 */
};


PyMODINIT_FUNC
initimp(void)
{
        PyObject *m, *d;

        if (PyType_Ready(&NullImporterType) < 0)
                goto failure;

        m = Py_InitModule4("imp", imp_methods, doc_imp,
                           NULL, PYTHON_API_VERSION);
        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(&NullImporterType);
        PyModule_AddObject(m, "NullImporter", (PyObject *)&NullImporterType);
  failure:
        ;
}


/* 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(char *name, void (*initfunc)(void))
{
        struct _inittab newtab[2];

        memset(newtab, '\0', sizeof newtab);

        newtab[0].name = name;
        newtab[0].initfunc = initfunc;

        return PyImport_ExtendInittab(newtab);
}

#ifdef __cplusplus
}
#endif