bpo-39947: Add PyInterpreterState_Get() function (GH-18979)

* Rename _PyInterpreterState_Get() to PyInterpreterState_Get() and
  move it the limited C API.
* Add _PyInterpreterState_Get() alias to PyInterpreterState_Get() for
  backward compatibility with Python 3.8.

2 files changed, 13 insertions, 7 deletions

diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index fbb0899..96df0d9 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -139,13 +139,8 @@ struct _ts {
 
 };
 
-/* Get the current interpreter state.
-
-   Issue a fatal error if there no current Python thread state or no current
-   interpreter. It cannot return NULL.
-
-   The caller must hold the GIL.*/
-PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_Get(void);
+// Alias for backward compatibility with Python 3.8
+#define _PyInterpreterState_Get PyInterpreterState_Get
 
 PyAPI_FUNC(PyThreadState *) _PyThreadState_Prealloc(PyInterpreterState *);
 
diff --git a/Include/pystate.h b/Include/pystate.h
index 1cb2305..57dc9e4 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -28,6 +28,17 @@ PyAPI_FUNC(PyInterpreterState *) PyInterpreterState_New(void);
 PyAPI_FUNC(void) PyInterpreterState_Clear(PyInterpreterState *);
 PyAPI_FUNC(void) PyInterpreterState_Delete(PyInterpreterState *);
 
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03090000
+/* New in 3.9 */
+/* Get the current interpreter state.
+
+   Issue a fatal error if there no current Python thread state or no current
+   interpreter. It cannot return NULL.
+
+   The caller must hold the GIL. */
+PyAPI_FUNC(PyInterpreterState *) PyInterpreterState_Get(void);
+#endif
+
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03080000
 /* New in 3.8 */
 PyAPI_FUNC(PyObject *) PyInterpreterState_GetDict(PyInterpreterState *);