bpo-22257: Private C-API for main interpreter initialization (PEP 432). (#1729)

(patch by Nick Coghlan)

Python/pythonrun.c

@@ -1,5 +1,12 @@
 
-/* Python interpreter top-level routines, including init/exit */
+/* Top level execution of Python code (including in __main__) */
+
+/* To help control the interfaces between the startup, execution and
+ * shutdown code, the phases are split across separate modules (boostrap,
+ * pythonrun, shutdown)
+ */
+
+/* TODO: Cull includes following phase split */
 
 #include "Python.h"
 
@@ -59,7 +66,6 @@ static void err_input(perrdetail *);
 static void err_free(perrdetail *);
 
 /* Parse input from a file and execute it */
-
 int
 PyRun_AnyFileExFlags(FILE *fp, const char *filename, int closeit,
                      PyCompilerFlags *flags)