From eec9331b207cf7def6f04156d00a8479d1630dd3 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Thu, 18 Aug 2016 18:13:10 +0200
Subject: [PATCH] Fix SystemError in "raise" statement

Issue #27558: Fix a SystemError in the implementation of "raise" statement.
In a brand new thread, raise a RuntimeError since there is no active
exception to reraise.

Patch written by Xiang Zhang.
---
 Lib/test/test_threading.py | 18 ++++++++++++++++++
 Misc/NEWS                  |  4 ++++
 Python/ceval.c             |  2 +-
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 1c9c1ea534e..b63050982ab 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -1043,6 +1043,24 @@ class ThreadingExceptionTests(BaseTestCase):
         self.assertEqual(out, b'')
         self.assertNotIn("Unhandled exception", err.decode())
 
+    def test_bare_raise_in_brand_new_thread(self):
+        def bare_raise():
+            raise
+
+        class Issue27558(threading.Thread):
+            exc = None
+
+            def run(self):
+                try:
+                    bare_raise()
+                except Exception as exc:
+                    self.exc = exc
+
+        thread = Issue27558()
+        thread.start()
+        thread.join()
+        self.assertIsNotNone(thread.exc)
+        self.assertIsInstance(thread.exc, RuntimeError)
 
 class TimerTests(BaseTestCase):
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 0946553db70..6c78a191e24 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,10 @@ Release date: TBA
 Core and Builtins
 -----------------
 
+- Issue #27558: Fix a SystemError in the implementation of "raise" statement.
+  In a brand new thread, raise a RuntimeError since there is no active
+  exception to reraise. Patch written by Xiang Zhang.
+
 - Issue #27419: Standard __import__() no longer look up "__import__" in globals
   or builtins for importing submodules or "from import".  Fixed handling an
   error of non-string package name.
diff --git a/Python/ceval.c b/Python/ceval.c
index c632488ec2c..8e396fd2bc6 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -4123,7 +4123,7 @@ do_raise(PyObject *exc, PyObject *cause)
         type = tstate->exc_type;
         value = tstate->exc_value;
         tb = tstate->exc_traceback;
-        if (type == Py_None) {
+        if (type == Py_None || type == NULL) {
             PyErr_SetString(PyExc_RuntimeError,
                             "No active exception to reraise");
             return 0;