From bf93b0470affd720a603805eb00c917a9bc39cc9 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Sun, 18 May 2008 07:46:13 +0000
Subject: [PATCH] Fix two issues in the weak set implementation.

---
 Lib/_weakrefset.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Lib/_weakrefset.py b/Lib/_weakrefset.py
index e56ac048dd5..a6827e8298e 100644
--- a/Lib/_weakrefset.py
+++ b/Lib/_weakrefset.py
@@ -41,7 +41,10 @@ class WeakSet:
 
     def pop(self):
         while True:
-            itemref = self.data.pop()
+            try:
+                itemref = self.data.pop()
+            except KeyError:
+                raise KeyError('pop from empty WeakSet')
             item = itemref()
             if item is not None:
                 return item
@@ -107,5 +110,5 @@ class WeakSet:
     __ixor__ = symmetric_difference_update
 
     def union(self, other):
-        self._apply_mutate(other, self.data.union)
+        return self._apply(other, self.data.union)
     __or__ = union