Index: Python/import.c
===================================================================
--- Python/import.c	(revision 57534)
+++ Python/import.c	(working copy)
@@ -104,7 +104,6 @@
 };
 #endif
 
-static PyTypeObject NullImporterType;	/* Forward reference */
 
 /* Initialize things */
 
@@ -167,7 +166,7 @@
 
 	/* adding sys.path_hooks and sys.path_importer_cache, setting up
 	   zipimport */
-	if (PyType_Ready(&NullImporterType) < 0)
+	if (PyType_Ready(&Py_NullImporterType) < 0)
 		goto error;
 
 	if (Py_VerboseFlag)
@@ -1088,7 +1087,7 @@
 	}
 	if (importer == NULL) {
 		importer = PyObject_CallFunctionObjArgs(
-			(PyObject *)&NullImporterType, p, NULL
+			(PyObject *)&Py_NullImporterType, p, NULL
 		);
 		if (importer == NULL) {
 			if (PyErr_ExceptionMatches(PyExc_ImportError)) {
@@ -1106,6 +1105,18 @@
 	return importer;
 }
 
+PyAPI_FUNC(PyObject *)
+PyImport_GetImporter(PyObject *path) {
+        PyObject *importer=NULL, *path_importer_cache=NULL, *path_hooks=NULL;
+
+	(path_importer_cache = PySys_GetObject("path_importer_cache")) &&
+	(path_hooks = PySys_GetObject("path_hooks")) &&
+ 	(importer = get_path_importer(path_importer_cache, path_hooks, path));
+
+	Py_XINCREF(importer); /* get_path_importer returns a borrowed reference */
+	return importer;
+}
+
 /* Search the path (default sys.path) for a module.  Return the
    corresponding filedescr struct, and (via return arguments) the
    pathname and an open file.  Return NULL if the module is not found. */
@@ -3033,7 +3044,7 @@
 };
 
 
-static PyTypeObject NullImporterType = {
+PyTypeObject Py_NullImporterType = {
 	PyVarObject_HEAD_INIT(NULL, 0)
 	"imp.NullImporter",        /*tp_name*/
 	sizeof(NullImporter),      /*tp_basicsize*/
@@ -3080,7 +3091,7 @@
 {
 	PyObject *m, *d;
 
-	if (PyType_Ready(&NullImporterType) < 0)
+	if (PyType_Ready(&Py_NullImporterType) < 0)
 		goto failure;
 
 	m = Py_InitModule4("imp", imp_methods, doc_imp,
@@ -3102,8 +3113,8 @@
 	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);
+	Py_INCREF(&Py_NullImporterType);
+	PyModule_AddObject(m, "NullImporter", (PyObject *)&Py_NullImporterType);
   failure:
 	;
 }
Index: Include/import.h
===================================================================
--- Include/import.h	(revision 57534)
+++ Include/import.h	(working copy)
@@ -24,6 +24,7 @@
 #define PyImport_ImportModuleEx(n, g, l, f) \
 	PyImport_ImportModuleLevel(n, g, l, f, -1)
 
+PyAPI_FUNC(PyObject *) PyImport_GetImporter(PyObject *path);
 PyAPI_FUNC(PyObject *) PyImport_Import(PyObject *name);
 PyAPI_FUNC(PyObject *) PyImport_ReloadModule(PyObject *m);
 PyAPI_FUNC(void) PyImport_Cleanup(void);
@@ -42,6 +43,7 @@
     void (*initfunc)(void);
 };
 
+PyAPI_DATA(PyTypeObject) Py_NullImporterType;
 PyAPI_DATA(struct _inittab *) PyImport_Inittab;
 
 PyAPI_FUNC(int) PyImport_AppendInittab(char *name, void (*initfunc)(void));
Index: Modules/main.c
===================================================================
--- Modules/main.c	(revision 57534)
+++ Modules/main.c	(working copy)
@@ -141,7 +141,7 @@
 }
 
 
-static int RunModule(char *module)
+static int RunModule(char *module, int set_argv0)
 {
 	PyObject *runpy, *runmodule, *runargs, *result;
 	runpy = PyImport_ImportModule("runpy");
@@ -155,7 +155,7 @@
 		Py_DECREF(runpy);
 		return -1;
 	}
-	runargs = Py_BuildValue("(s)", module);
+	runargs = Py_BuildValue("(si)", module, set_argv0);
 	if (runargs == NULL) {
 		fprintf(stderr,
 			"Could not create arguments for runpy._run_module_as_main\n");
@@ -177,6 +177,35 @@
 	return 0;
 }
 
+static int RunMainFromImporter(char *filename)
+{
+	PyObject *argv0 = NULL, *importer = NULL;
+
+	if (
+		(argv0 = PyString_FromString(filename)) && 
+		(importer = PyImport_GetImporter(argv0)) &&
+		(importer->ob_type != &Py_NullImporterType)
+	)  {
+		 /* argv0 is usable as an import source, so
+			put it in sys.path[0] and import __main__ */
+		PyObject *sys_path = NULL;
+		if (
+			(sys_path = PySys_GetObject("path")) &&
+			!PyList_SetItem(sys_path, 0, argv0)
+		) {
+			Py_INCREF(argv0);
+			Py_CLEAR(importer);
+			sys_path = NULL;
+			return RunModule("__main__", 0) != 0;
+		}
+	}
+	PyErr_Clear();
+	Py_CLEAR(argv0);
+	Py_CLEAR(importer);
+	return -1;
+}
+
+
 /* Wait until threading._shutdown completes, provided
    the threading module was imported in the first place.
    The shutdown routine will wait until all non-daemon
@@ -388,38 +417,6 @@
 #else
 		filename = argv[_PyOS_optind];
 #endif
-		if (filename != NULL) {
-			if ((fp = fopen(filename, "r")) == NULL) {
-#ifdef HAVE_STRERROR
-				fprintf(stderr, "%s: can't open file '%s': [Errno %d] %s\n",
-					argv[0], filename, errno, strerror(errno));
-#else
-				fprintf(stderr, "%s: can't open file '%s': Errno %d\n",
-					argv[0], filename, errno);
-#endif
-				return 2;
-			}
-			else if (skipfirstline) {
-				int ch;
-				/* Push back first newline so line numbers
-				   remain the same */
-				while ((ch = getc(fp)) != EOF) {
-					if (ch == '\n') {
-						(void)ungetc(ch, fp);
-						break;
-					}
-				}
-			}
-			{
-				/* XXX: does this work on Win/Win64? (see posix_fstat) */
-				struct stat sb;
-				if (fstat(fileno(fp), &sb) == 0 &&
-				    S_ISDIR(sb.st_mode)) {
-					fprintf(stderr, "%s: '%s' is a directory, cannot continue\n", argv[0], filename);
-					return 1;
-				}
-			}
-		}
 	}
 
 	stdin_is_interactive = Py_FdIsInteractive(stdin, (char *)0);
@@ -514,19 +511,63 @@
 		sts = PyRun_SimpleStringFlags(command, &cf) != 0;
 		free(command);
 	} else if (module) {
-		sts = RunModule(module);
+		sts = RunModule(module, 1);
 		free(module);
 	}
 	else {
+
 		if (filename == NULL && stdin_is_interactive) {
 			Py_InspectFlag = 0; /* do exit on SystemExit */
 			RunStartupFile(&cf);
 		}
 		/* XXX */
-		sts = PyRun_AnyFileExFlags(
-			fp,
-			filename == NULL ? "<stdin>" : filename,
-			filename != NULL, &cf) != 0;
+
+		sts = -1;	/* keep track of whether we've already run __main__ */
+
+		if (filename != NULL) {
+			sts = RunMainFromImporter(filename);
+		}
+
+		if (sts==-1 && filename!=NULL) {
+			if ((fp = fopen(filename, "r")) == NULL) {
+#ifdef HAVE_STRERROR
+				fprintf(stderr, "%s: can't open file '%s': [Errno %d] %s\n",
+					argv[0], filename, errno, strerror(errno));
+#else
+				fprintf(stderr, "%s: can't open file '%s': Errno %d\n",
+					argv[0], filename, errno);
+#endif
+				return 2;
+			}
+			else if (skipfirstline) {
+				int ch;
+				/* Push back first newline so line numbers
+				   remain the same */
+				while ((ch = getc(fp)) != EOF) {
+					if (ch == '\n') {
+						(void)ungetc(ch, fp);
+						break;
+					}
+				}
+			}
+			{
+				/* XXX: does this work on Win/Win64? (see posix_fstat) */
+				struct stat sb;
+				if (fstat(fileno(fp), &sb) == 0 &&
+				    S_ISDIR(sb.st_mode)) {
+					fprintf(stderr, "%s: '%s' is a directory, cannot continue\n", argv[0], filename);
+					return 1;
+				}
+			}
+		}
+
+		if (sts==-1) {
+			sts = PyRun_AnyFileExFlags(
+				fp,
+				filename == NULL ? "<stdin>" : filename,
+				filename != NULL, &cf) != 0;
+		}
+		
 	}
 
 	/* Check this environment variable at the end, to give programs the