Fix a conversion mistake that caused test_queue to fail intermittently.

Lib/test/test_queue.py

@@ -138,13 +138,13 @@ class BaseQueueTest(unittest.TestCase, BlockingTestMixin):
 
     def worker(self, q):
         while True:
-            self.x = q.get()
+            x = q.get()
-            if self.x is None:
+            if x is None:
                 q.task_done()
                 return
             self.cumlock.acquire()
             try:
-                self.cum += self.x
+                self.cum += x
             finally:
                 self.cumlock.release()
             q.task_done()