bpo-36763: Add _Py_InitializeMain() (GH-13362)

* Add a private _Py_InitializeMain() function.
* Add again _PyCoreConfig._init_main.
* _Py_InitializeFromConfig() now uses _init_main to decide
  if _Py_InitializeMainInterpreter() should be called.
* _PyCoreConfig: rename _frozen to pathconfig_warnings, its value is
  now the opposite of Py_FrozenFlag.
* Add an unit test for _init_main=0 and _Py_InitializeMain().

1 files changed, 9 insertions, 0 deletions

diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 3d83044af9..bc131fd7e5 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -1046,6 +1046,15 @@ run_eval_code_obj(PyCodeObject *co, PyObject *globals, PyObject *locals)
      * Py_Main() based one.
      */
     _Py_UnhandledKeyboardInterrupt = 0;
+
+    /* Set globals['__builtins__'] if it doesn't exist */
+    if (globals != NULL && PyDict_GetItemString(globals, "__builtins__") == NULL) {
+        PyInterpreterState *interp = _PyInterpreterState_Get();
+        if (PyDict_SetItemString(globals, "__builtins__", interp->builtins) < 0) {
+            return NULL;
+        }
+    }
+
     v = PyEval_EvalCode((PyObject*)co, globals, locals);
     if (!v && PyErr_Occurred() == PyExc_KeyboardInterrupt) {
         _Py_UnhandledKeyboardInterrupt = 1;