# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1486315084 -3600
# Node ID 529270fc78bdc99cc8c3d5bac5b44eaab6335a92
# Parent  1eb65d050225c357701855bd16b332fd6e2c4f31
Fixed various update operations and expanded the test of sets.

diff -r 1eb65d050225 -r 529270fc78bd lib/__builtins__/set.py
--- a/lib/__builtins__/set.py	Sun Feb 05 18:17:14 2017 +0100
+++ b/lib/__builtins__/set.py	Sun Feb 05 18:18:04 2017 +0100
@@ -239,7 +239,7 @@
         "Remove from this set all values from 'other'."
 
         for value in other:
-            self.remove(value)
+            self.discard(value)
 
     def discard(self, value):
 
@@ -254,9 +254,14 @@
 
         "Preserve in this set only values in this set found in 'other'."
 
+        to_remove = set()
+
         for value in self:
             if value not in other:
-                self.remove(value)
+                to_remove.add(value)
+
+        for value in to_remove:
+            self.remove(value)
 
     def pop(self):
 
diff -r 1eb65d050225 -r 529270fc78bd tests/set.py
--- a/tests/set.py	Sun Feb 05 18:17:14 2017 +0100
+++ b/tests/set.py	Sun Feb 05 18:18:04 2017 +0100
@@ -51,3 +51,20 @@
 print 9 in aib                      # False
 print 9 in adb                      # True
 print 9 in asdb                     # False
+print
+
+aub2 = a.copy()
+aub2.update(b)
+print len(aub2)                     # 6
+
+aib2 = a.copy()
+aib2.intersection_update(b)
+print len(aib2)                     # 4
+
+adb2 = a.copy()
+adb2.difference_update(b)
+print len(adb2)                     # 1
+
+asdb2 = a.copy()
+asdb2.symmetric_difference_update(b)
+print len(asdb2)                    # 2