Fix some set algebra methods of WeakSet objects.

1 files changed, 12 insertions, 29 deletions

diff --git a/Lib/_weakrefset.py b/Lib/_weakrefset.py
index c2717e7..1f41841 100644
--- a/Lib/_weakrefset.py
+++ b/Lib/_weakrefset.py
@@ -121,26 +121,14 @@ class WeakSet:
         self.update(other)
         return self
 
-    # Helper functions for simple delegating methods.
-    def _apply(self, other, method):
-        if not isinstance(other, self.__class__):
-            other = self.__class__(other)
-        newdata = method(other.data)
-        newset = self.__class__()
-        newset.data = newdata
-        return newset
-
     def difference(self, other):
-        return self._apply(other, self.data.difference)
+        newset = self.copy()
+        newset.difference_update(other)
+        return newset
     __sub__ = difference
 
     def difference_update(self, other):
-        if self._pending_removals:
-            self._commit_removals()
-        if self is other:
-            self.data.clear()
-        else:
-            self.data.difference_update(ref(item) for item in other)
+        self.__isub__(other)
     def __isub__(self, other):
         if self._pending_removals:
             self._commit_removals()
@@ -151,13 +139,11 @@ class WeakSet:
         return self
 
     def intersection(self, other):
-        return self._apply(other, self.data.intersection)
+        return self.__class__(item for item in other if item in self)
     __and__ = intersection
 
     def intersection_update(self, other):
-        if self._pending_removals:
-            self._commit_removals()
-        self.data.intersection_update(ref(item) for item in other)
+        self.__iand__(other)
     def __iand__(self, other):
         if self._pending_removals:
             self._commit_removals()
@@ -184,27 +170,24 @@ class WeakSet:
         return self.data == set(ref(item) for item in other)
 
     def symmetric_difference(self, other):
-        return self._apply(other, self.data.symmetric_difference)
+        newset = self.copy()
+        newset.symmetric_difference_update(other)
+        return newset
     __xor__ = symmetric_difference
 
     def symmetric_difference_update(self, other):
-        if self._pending_removals:
-            self._commit_removals()
-        if self is other:
-            self.data.clear()
-        else:
-            self.data.symmetric_difference_update(ref(item) for item in other)
+        self.__ixor__(other)
     def __ixor__(self, other):
         if self._pending_removals:
             self._commit_removals()
         if self is other:
             self.data.clear()
         else:
-            self.data.symmetric_difference_update(ref(item) for item in other)
+            self.data.symmetric_difference_update(ref(item, self._remove) for item in other)
         return self
 
     def union(self, other):
-        return self._apply(other, self.data.union)
+        return self.__class__(e for s in (self, other) for e in s)
     __or__ = union
 
     def isdisjoint(self, other):