bpo-28411: Support other mappings in PyInterpreterState.modules. (#3593)

The concrete PyDict_* API is used to interact with PyInterpreterState.modules in a number of places. This isn't compatible with all dict subclasses, nor with other Mapping implementations. This patch switches the concrete API usage to the corresponding abstract API calls.

We also add a PyImport_GetModule() function (and some other helpers) to reduce a bunch of code duplication.

Doc/c-api/import.rst

@@ -204,6 +204,13 @@ Importing Modules
    Return the dictionary used for the module administration (a.k.a.
    ``sys.modules``).  Note that this is a per-interpreter variable.
 
+.. c:function:: PyObject* PyImport_GetModule(PyObject *name)
+
+   Return the already imported module with the given name.  If the
+   module has not been imported yet then returns NULL but does not set
+   an error.  Returns NULL and sets an error if the lookup failed.
+
+   .. versionadded:: 3.7
 
 .. c:function:: PyObject* PyImport_GetImporter(PyObject *path)
 

Include/import.h

@@ -38,8 +38,14 @@ PyAPI_FUNC(PyObject *) PyImport_ExecCodeModuleObject(
     );
 #endif
 PyAPI_FUNC(PyObject *) PyImport_GetModuleDict(void);
+PyAPI_FUNC(PyObject *) PyImport_GetModule(PyObject *name);
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(int) _PyImport_IsInitialized(PyInterpreterState *);
+PyAPI_FUNC(PyObject *) _PyImport_GetModuleId(struct _Py_Identifier *name);
+PyAPI_FUNC(PyObject *) _PyImport_AddModuleObject(PyObject *name,
+                                                 PyObject *modules);
+PyAPI_FUNC(int) _PyImport_SetModule(PyObject *name, PyObject *module);
+PyAPI_FUNC(int) _PyImport_SetModuleString(const char *name, PyObject* module);
 #endif
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03030000
 PyAPI_FUNC(PyObject *) PyImport_AddModuleObject(

Misc/NEWS.d/next/Core and Builtins/2017-09-11-09-11-20.bpo-28411.Ax91lz.rst

+Switch to the abstract API when dealing with ``PyInterpreterState.modules``.
+This allows later support for all dict subclasses and other Mapping
+implementations.  Also add a ``PyImport_GetModule()`` function to reduce
+a bunch of duplicated code.

Modules/_pickle.c

@@ -1649,13 +1649,40 @@ getattribute(PyObject *obj, PyObject *name, int allow_qualname)
     return attr;
 }
 
+static int
+_checkmodule(PyObject *module_name, PyObject *module,
+             PyObject *global, PyObject *dotted_path)
+{
+    if (module == Py_None) {
+        return -1;
+    }
+    if (PyUnicode_Check(module_name) &&
+            _PyUnicode_EqualToASCIIString(module_name, "__main__")) {
+        return -1;
+    }
+
+    PyObject *candidate = get_deep_attribute(module, dotted_path, NULL);
+    if (candidate == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+            PyErr_Clear();
+        }
+        return -1;
+    }
+    if (candidate != global) {
+        Py_DECREF(candidate);
+        return -1;
+    }
+    Py_DECREF(candidate);
+    return 0;
+}
+
 static PyObject *
 whichmodule(PyObject *global, PyObject *dotted_path)
 {
     PyObject *module_name;
-    PyObject *modules_dict;
-    PyObject *module;
+    PyObject *module = NULL;
     Py_ssize_t i;
+    PyObject *modules;
     _Py_IDENTIFIER(__module__);
     _Py_IDENTIFIER(modules);
     _Py_IDENTIFIER(__main__);
@@ -1678,35 +1705,48 @@ whichmodule(PyObject *global, PyObject *dotted_path)
     assert(module_name == NULL);
 
     /* Fallback on walking sys.modules */
-    modules_dict = _PySys_GetObjectId(&PyId_modules);
-    if (modules_dict == NULL) {
+    modules = _PySys_GetObjectId(&PyId_modules);
+    if (modules == NULL) {
         PyErr_SetString(PyExc_RuntimeError, "unable to get sys.modules");
         return NULL;
     }
-
-    i = 0;
-    while (PyDict_Next(modules_dict, &i, &module_name, &module)) {
-        PyObject *candidate;
-        if (PyUnicode_Check(module_name) &&
-            _PyUnicode_EqualToASCIIString(module_name, "__main__"))
-            continue;
-        if (module == Py_None)
-            continue;
-
-        candidate = get_deep_attribute(module, dotted_path, NULL);
-        if (candidate == NULL) {
-            if (!PyErr_ExceptionMatches(PyExc_AttributeError))
+    if (PyDict_CheckExact(modules)) {
+        i = 0;
+        while (PyDict_Next(modules, &i, &module_name, &module)) {
+            if (_checkmodule(module_name, module, global, dotted_path) == 0) {
+                Py_INCREF(module_name);
+                return module_name;
+            }
+            if (PyErr_Occurred()) {
                 return NULL;
-            PyErr_Clear();
-            continue;
+            }
         }
-
-        if (candidate == global) {
-            Py_INCREF(module_name);
-            Py_DECREF(candidate);
-            return module_name;
+    }
+    else {
+        PyObject *iterator = PyObject_GetIter(modules);
+        if (iterator == NULL) {
+            return NULL;
         }
-        Py_DECREF(candidate);
+        while ((module_name = PyIter_Next(iterator))) {
+            module = PyObject_GetItem(modules, module_name);
+            if (module == NULL) {
+                Py_DECREF(module_name);
+                Py_DECREF(iterator);
+                return NULL;
+            }
+            if (_checkmodule(module_name, module, global, dotted_path) == 0) {
+                Py_DECREF(module);
+                Py_DECREF(iterator);
+                return module_name;
+            }
+            Py_DECREF(module);
+            Py_DECREF(module_name);
+            if (PyErr_Occurred()) {
+                Py_DECREF(iterator);
+                return NULL;
+            }
+        }
+        Py_DECREF(iterator);
     }
 
     /* If no module is found, use __main__. */
@@ -6424,9 +6464,7 @@ _pickle_Unpickler_find_class_impl(UnpicklerObject *self,
 /*[clinic end generated code: output=becc08d7f9ed41e3 input=e2e6a865de093ef4]*/
 {
     PyObject *global;
-    PyObject *modules_dict;
     PyObject *module;
-    _Py_IDENTIFIER(modules);
 
     /* Try to map the old names used in Python 2.x to the new ones used in
        Python 3.x.  We do this only with old pickle protocols and when the
@@ -6483,25 +6521,16 @@ _pickle_Unpickler_find_class_impl(UnpicklerObject *self,
         }
     }
 
-    modules_dict = _PySys_GetObjectId(&PyId_modules);
-    if (modules_dict == NULL) {
-        PyErr_SetString(PyExc_RuntimeError, "unable to get sys.modules");
-        return NULL;
-    }
-
-    module = PyDict_GetItemWithError(modules_dict, module_name);
+    module = PyImport_GetModule(module_name);
     if (module == NULL) {
         if (PyErr_Occurred())
             return NULL;
         module = PyImport_Import(module_name);
         if (module == NULL)
             return NULL;
-        global = getattribute(module, global_name, self->proto >= 4);
-        Py_DECREF(module);
-    }
-    else {
-        global = getattribute(module, global_name, self->proto >= 4);
     }
+    global = getattribute(module, global_name, self->proto >= 4);
+    Py_DECREF(module);
     return global;
 }
 

Modules/pyexpat.c

@@ -1643,7 +1643,6 @@ MODULE_INITFUNC(void)
     PyObject *errors_module;
     PyObject *modelmod_name;
     PyObject *model_module;
-    PyObject *sys_modules;
     PyObject *tmpnum, *tmpstr;
     PyObject *codes_dict;
     PyObject *rev_codes_dict;
@@ -1693,11 +1692,6 @@ MODULE_INITFUNC(void)
     */
     PyModule_AddStringConstant(m, "native_encoding", "UTF-8");
 
-    sys_modules = PySys_GetObject("modules");
-    if (sys_modules == NULL) {
-        Py_DECREF(m);
-        return NULL;
-    }
     d = PyModule_GetDict(m);
     if (d == NULL) {
         Py_DECREF(m);
@@ -1707,7 +1701,7 @@ MODULE_INITFUNC(void)
     if (errors_module == NULL) {
         errors_module = PyModule_New(MODULE_NAME ".errors");
         if (errors_module != NULL) {
-            PyDict_SetItem(sys_modules, errmod_name, errors_module);
+            _PyImport_SetModule(errmod_name, errors_module);
             /* gives away the reference to errors_module */
             PyModule_AddObject(m, "errors", errors_module);
         }
@@ -1717,7 +1711,7 @@ MODULE_INITFUNC(void)
     if (model_module == NULL) {
         model_module = PyModule_New(MODULE_NAME ".model");
         if (model_module != NULL) {
-            PyDict_SetItem(sys_modules, modelmod_name, model_module);
+            _PyImport_SetModule(modelmod_name, model_module);
             /* gives away the reference to model_module */
             PyModule_AddObject(m, "model", model_module);
         }

Objects/typeobject.c

@@ -3913,10 +3913,8 @@ import_copyreg(void)
        by storing a reference to the cached module in a static variable, but
        this broke when multiple embedded interpreters were in use (see issue
        #17408 and #19088). */
-    PyObject *modules = PyImport_GetModuleDict();
-    copyreg_module = PyDict_GetItemWithError(modules, copyreg_str);
+    copyreg_module = PyImport_GetModule(copyreg_str);
     if (copyreg_module != NULL) {
-        Py_INCREF(copyreg_module);
         return copyreg_module;
     }
     if (PyErr_Occurred()) {

Python/_warnings.c

@@ -38,7 +38,6 @@ static PyObject *
 get_warnings_attr(const char *attr, int try_import)
 {
     static PyObject *warnings_str = NULL;
-    PyObject *all_modules;
     PyObject *warnings_module, *obj;
 
     if (warnings_str == NULL) {
@@ -58,13 +57,9 @@ get_warnings_attr(const char *attr, int try_import)
         }
     }
     else {
-        all_modules = PyImport_GetModuleDict();
-
-        warnings_module = PyDict_GetItem(all_modules, warnings_str);
+        warnings_module = PyImport_GetModule(warnings_str);
         if (warnings_module == NULL)
             return NULL;
-
-        Py_INCREF(warnings_module);
     }
 
     if (!PyObject_HasAttrString(warnings_module, attr)) {

Python/ceval.c

@@ -4935,13 +4935,12 @@ import_from(PyObject *v, PyObject *name)
         Py_DECREF(pkgname);
         return NULL;
     }
-    x = PyDict_GetItem(PyImport_GetModuleDict(), fullmodname);
+    x = PyImport_GetModule(fullmodname);
     Py_DECREF(fullmodname);
     if (x == NULL) {
         goto error;
     }
     Py_DECREF(pkgname);
-    Py_INCREF(x);
     return x;
  error:
     pkgpath = PyModule_GetFilenameObject(v);

Python/import.c

@@ -291,8 +291,9 @@ PyObject *
 PyImport_GetModuleDict(void)
 {
     PyInterpreterState *interp = PyThreadState_GET()->interp;
-    if (interp->modules == NULL)
+    if (interp->modules == NULL) {
         Py_FatalError("PyImport_GetModuleDict: no module dictionary!");
+    }
     return interp->modules;
 }
 
@@ -308,6 +309,55 @@ _PyImport_IsInitialized(PyInterpreterState *interp)
     return 1;
 }
 
+PyObject *
+_PyImport_GetModuleId(struct _Py_Identifier *nameid)
+{
+    PyObject *name = _PyUnicode_FromId(nameid); /* borrowed */
+    if (name == NULL) {
+        return NULL;
+    }
+    return PyImport_GetModule(name);
+}
+
+int
+_PyImport_SetModule(PyObject *name, PyObject *m)
+{
+    PyObject *modules = PyImport_GetModuleDict();
+    return PyObject_SetItem(modules, name, m);
+}
+
+int
+_PyImport_SetModuleString(const char *name, PyObject *m)
+{
+    PyObject *modules = PyImport_GetModuleDict();
+    return PyMapping_SetItemString(modules, name, m);
+}
+
+PyObject *
+PyImport_GetModule(PyObject *name)
+{
+    PyObject *m;
+    PyObject *modules = PyImport_GetModuleDict();
+    if (modules == NULL) {
+        PyErr_SetString(PyExc_RuntimeError, "unable to get sys.modules");
+        return NULL;
+    }
+    Py_INCREF(modules);
+    if (PyDict_CheckExact(modules)) {
+        m = PyDict_GetItemWithError(modules, name);  /* borrowed */
+        Py_XINCREF(m);
+    }
+    else {
+        m = PyObject_GetItem(modules, name);
+        if (PyErr_ExceptionMatches(PyExc_KeyError)) {
+            PyErr_Clear();
+        }
+    }
+    Py_DECREF(modules);
+    return m;
+}
+
+
 /* List of names to clear in sys */
 static const char * const sys_deletes[] = {
     "path", "argv", "ps1", "ps2",
@@ -387,21 +437,51 @@ PyImport_Cleanup(void)
         if (PyErr_Occurred()) \
             PyErr_Clear(); \
     }
+#define CLEAR_MODULE(name, mod) \
+    if (PyModule_Check(mod)) { \
+        if (Py_VerboseFlag && PyUnicode_Check(name)) \
+            PySys_FormatStderr("# cleanup[2] removing %U\n", name); \
+        STORE_MODULE_WEAKREF(name, mod); \
+        PyObject_SetItem(modules, name, Py_None); \
+    }
 
     /* Remove all modules from sys.modules, hoping that garbage collection
        can reclaim most of them. */
-    pos = 0;
-    while (PyDict_Next(modules, &pos, &key, &value)) {
-        if (PyModule_Check(value)) {
-            if (Py_VerboseFlag && PyUnicode_Check(key))
-                PySys_FormatStderr("# cleanup[2] removing %U\n", key);
-            STORE_MODULE_WEAKREF(key, value);
-            PyDict_SetItem(modules, key, Py_None);
+    if (PyDict_CheckExact(modules)) {
+        pos = 0;
+        while (PyDict_Next(modules, &pos, &key, &value)) {
+            CLEAR_MODULE(key, value);
+        }
+    }
+    else {
+        PyObject *iterator = PyObject_GetIter(modules);
+        if (iterator == NULL) {
+            PyErr_Clear();
+        }
+        else {
+            while ((key = PyIter_Next(iterator))) {
+                value = PyObject_GetItem(modules, key);
+                if (value == NULL) {
+                    PyErr_Clear();
+                    continue;
+                }
+                CLEAR_MODULE(key, value);
+                Py_DECREF(value);
+                Py_DECREF(key);
+            }
+            Py_DECREF(iterator);
         }
     }
 
     /* Clear the modules dict. */
-    PyDict_Clear(modules);
+    if (PyDict_CheckExact(modules)) {
+        PyDict_Clear(modules);
+    }
+    else {
+        _Py_IDENTIFIER(clear);
+        if (_PyObject_CallMethodId(modules, &PyId_clear, "") == NULL)
+            PyErr_Clear();
+    }
     /* Restore the original builtins dict, to ensure that any
        user data gets cleared. */
     dict = PyDict_Copy(interp->builtins);
@@ -541,10 +621,10 @@ _PyImport_FixupExtensionObject(PyObject *mod, PyObject *name,
         PyErr_BadInternalCall();
         return -1;
     }
-    if (PyDict_SetItem(modules, name, mod) < 0)
+    if (PyObject_SetItem(modules, name, mod) < 0)
         return -1;
     if (_PyState_AddModule(mod, def) < 0) {
-        PyDict_DelItem(modules, name);
+        PyMapping_DelItem(modules, name);
         return -1;
     }
     if (def->m_size == -1) {
@@ -625,14 +705,14 @@ _PyImport_FindExtensionObjectEx(PyObject *name, PyObject *filename,
         mod = def->m_base.m_init();
         if (mod == NULL)
             return NULL;
-        if (PyDict_SetItem(modules, name, mod) == -1) {
+        if (PyObject_SetItem(modules, name, mod) == -1) {
             Py_DECREF(mod);
             return NULL;
         }
         Py_DECREF(mod);
     }
     if (_PyState_AddModule(mod, def) < 0) {
-        PyDict_DelItem(modules, name);
+        PyMapping_DelItem(modules, name);
         Py_DECREF(mod);
         return NULL;
     }
@@ -672,18 +752,27 @@ PyObject *
 _PyImport_AddModuleObject(PyObject *name, PyObject *modules)
 {
     PyObject *m;
-
-    if ((m = PyDict_GetItemWithError(modules, name)) != NULL &&
-        PyModule_Check(m)) {
-        return m;
+    if (PyDict_CheckExact(modules)) {
+        m = PyDict_GetItemWithError(modules, name);
+    }
+    else {
+        m = PyObject_GetItem(modules, name);
+        // For backward-comaptibility we copy the behavior
+        // of PyDict_GetItemWithError().
+        if (PyErr_ExceptionMatches(PyExc_KeyError)) {
+            PyErr_Clear();
+        }
     }
     if (PyErr_Occurred()) {
         return NULL;
     }
+    if (m != NULL && PyModule_Check(m)) {
+        return m;
+    }
     m = PyModule_NewObject(name);
     if (m == NULL)
         return NULL;
-    if (PyDict_SetItem(modules, name, m) != 0) {
+    if (PyObject_SetItem(modules, name, m) != 0) {
         Py_DECREF(m);
         return NULL;
     }
@@ -710,11 +799,13 @@ static void
 remove_module(PyObject *name)
 {
     PyObject *modules = PyImport_GetModuleDict();
-    if (PyDict_GetItem(modules, name) == NULL)
-        return;
-    if (PyDict_DelItem(modules, name) < 0)
+    if (PyMapping_DelItem(modules, name) < 0) {
+        if (!PyMapping_HasKey(modules, name)) {
+            return;
+        }
         Py_FatalError("import:  deleting existing key in"
                       "sys.modules failed");
+    }
 }
 
 
@@ -823,7 +914,6 @@ module_dict_for_exec(PyObject *name)
 static PyObject *
 exec_code_in_module(PyObject *name, PyObject *module_dict, PyObject *code_object)
 {
-    PyObject *modules = PyImport_GetModuleDict();
     PyObject *v, *m;
 
     v = PyEval_EvalCode(code_object, module_dict, module_dict);
@@ -833,15 +923,14 @@ exec_code_in_module(PyObject *name, PyObject *module_dict, PyObject *code_object
     }
     Py_DECREF(v);
 
-    if ((m = PyDict_GetItem(modules, name)) == NULL) {
+    m = PyImport_GetModule(name);
+    if (m == NULL) {
         PyErr_Format(PyExc_ImportError,
                      "Loaded module %R not found in sys.modules",
                      name);
         return NULL;
     }
 
-    Py_INCREF(m);
-
     return m;
 }
 
@@ -1540,8 +1629,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         Py_INCREF(abs_name);
     }
 
-    PyObject *modules = PyImport_GetModuleDict();
-    mod = PyDict_GetItem(modules, abs_name);
+    mod = PyImport_GetModule(abs_name);
     if (mod != NULL && mod != Py_None) {
         _Py_IDENTIFIER(__spec__);
         _Py_IDENTIFIER(_initializing);
@@ -1550,7 +1638,6 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         PyObject *spec;
         int initializing = 0;
 
-        Py_INCREF(mod);
         /* Optimization: only call _bootstrap._lock_unlock_module() if
            __spec__._initializing is true.
            NOTE: because of this, initializing must be set *before*
@@ -1579,6 +1666,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         }
     }
     else {
+        Py_XDECREF(mod);
         mod = _PyObject_CallMethodIdObjArgs(interp->importlib,
                                             &PyId__find_and_load, abs_name,
                                             interp->import_func, NULL);
@@ -1628,8 +1716,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                     goto error;
                 }
 
-                PyObject *modules = PyImport_GetModuleDict();
-                final_mod = PyDict_GetItem(modules, to_return);
+                final_mod = PyImport_GetModule(to_return);
                 Py_DECREF(to_return);
                 if (final_mod == NULL) {
                     PyErr_Format(PyExc_KeyError,
@@ -1637,7 +1724,6 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                                  to_return);
                     goto error;
                 }
-                Py_INCREF(final_mod);
             }
         }
         else {
@@ -1682,19 +1768,16 @@ PyImport_ImportModuleLevel(const char *name, PyObject *globals, PyObject *locals
 PyObject *
 PyImport_ReloadModule(PyObject *m)
 {
+    _Py_IDENTIFIER(imp);
     _Py_IDENTIFIER(reload);
     PyObject *reloaded_module = NULL;
-    PyObject *modules = PyImport_GetModuleDict();
-    PyObject *imp = PyDict_GetItemString(modules, "imp");
+    PyObject *imp = _PyImport_GetModuleId(&PyId_imp);
     if (imp == NULL) {
         imp = PyImport_ImportModule("imp");
         if (imp == NULL) {
             return NULL;
         }
     }
-    else {
-        Py_INCREF(imp);
-    }
 
     reloaded_module = _PyObject_CallMethodIdObjArgs(imp, &PyId_reload, m, NULL);
     Py_DECREF(imp);
@@ -1720,7 +1803,6 @@ PyImport_Import(PyObject *module_name)
     PyObject *globals = NULL;
     PyObject *import = NULL;
     PyObject *builtins = NULL;
-    PyObject *modules = NULL;
     PyObject *r = NULL;
 
     /* Initialize constant string objects */
@@ -1775,12 +1857,8 @@ PyImport_Import(PyObject *module_name)
         goto err;
     Py_DECREF(r);
 
-    modules = PyImport_GetModuleDict();
-    r = PyDict_GetItemWithError(modules, module_name);
-    if (r != NULL) {
-        Py_INCREF(r);
-    }
-    else if (!PyErr_Occurred()) {
+    r = PyImport_GetModule(module_name);
+    if (r == NULL && !PyErr_Occurred()) {
         PyErr_SetObject(PyExc_KeyError, module_name);
     }
 

Python/pylifecycle.c

@@ -42,6 +42,7 @@ _Py_IDENTIFIER(name);
 _Py_IDENTIFIER(stdin);
 _Py_IDENTIFIER(stdout);
 _Py_IDENTIFIER(stderr);
+_Py_IDENTIFIER(threading);
 
 #ifdef __cplusplus
 extern "C" {
@@ -283,7 +284,6 @@ initimport(PyInterpreterState *interp, PyObject *sysmod)
 {
     PyObject *importlib;
     PyObject *impmod;
-    PyObject *sys_modules;
     PyObject *value;
 
     /* Import _importlib through its frozen version, _frozen_importlib. */
@@ -314,11 +314,7 @@ initimport(PyInterpreterState *interp, PyObject *sysmod)
     else if (Py_VerboseFlag) {
         PySys_FormatStderr("import _imp # builtin\n");
     }
-    sys_modules = PyImport_GetModuleDict();
-    if (Py_VerboseFlag) {
-        PySys_FormatStderr("import sys # builtin\n");
-    }
-    if (PyDict_SetItemString(sys_modules, "_imp", impmod) < 0) {
+    if (_PyImport_SetModuleString("_imp", impmod) < 0) {
         Py_FatalError("Py_Initialize: can't save _imp to sys.modules");
     }
 
@@ -1916,8 +1912,7 @@ wait_for_thread_shutdown(void)
 {
     _Py_IDENTIFIER(_shutdown);
     PyObject *result;
-    PyObject *modules = PyImport_GetModuleDict();
-    PyObject *threading = PyMapping_GetItemString(modules, "threading");
+    PyObject *threading = _PyImport_GetModuleId(&PyId_threading);
     if (threading == NULL) {
         /* threading not imported */
         PyErr_Clear();

Python/sysmodule.c

@@ -162,18 +162,16 @@ static PyObject *
 sys_displayhook(PyObject *self, PyObject *o)
 {
     PyObject *outf;
-    PyObject *modules = PyImport_GetModuleDict();
-    if (modules == NULL)
-        return NULL;
     PyObject *builtins;
     static PyObject *newline = NULL;
     int err;
 
-    builtins = _PyDict_GetItemId(modules, &PyId_builtins);
+    builtins = _PyImport_GetModuleId(&PyId_builtins);
     if (builtins == NULL) {
         PyErr_SetString(PyExc_RuntimeError, "lost builtins module");
         return NULL;
     }
+    Py_DECREF(builtins);
 
     /* Print value except if None */
     /* After printing, also assign to '_' */