diff --git a/Lib/_weakrefset.py b/Lib/_weakrefset.py
index a6827e8..0046133 100644
--- a/Lib/_weakrefset.py
+++ b/Lib/_weakrefset.py
@@ -23,6 +23,9 @@
             if item is not None:
                 yield item
 
+    def __len__(self):
+        return sum(x() is not None for x in self.data)
+
     def __contains__(self, item):
         return ref(item) in self.data
 
@@ -61,7 +64,9 @@
         else:
             for element in other:
                 self.add(element)
-    __ior__ = update
+    def __ior__(self, other):
+        self.update(other)
+        return self
 
     # Helper functions for simple delegating methods.
     def _apply(self, other, method):
@@ -72,43 +77,68 @@
         newset.data = newdata
         return newset
 
-    def _apply_mutate(self, other, method):
-        if not isinstance(other, self.__class__):
-            other = self.__class__(other)
-        method(other)
-
     def difference(self, other):
         return self._apply(other, self.data.difference)
     __sub__ = difference
 
     def difference_update(self, other):
-        self._apply_mutate(self, self.data.difference_update)
-    __isub__ = difference_update
+        if self is other:
+            self.data.clear()
+        else:
+            self.data.difference_update(ref(item) for item in other)
+    def __isub__(self, other):
+        if self is other:
+            self.data.clear()
+        else:
+            self.data.difference_update(ref(item) for item in other)
+        return self
 
     def intersection(self, other):
         return self._apply(other, self.data.intersection)
     __and__ = intersection
 
     def intersection_update(self, other):
-        self._apply_mutate(self, self.data.intersection_update)
-    __iand__ = intersection_update
+        self.data.intersection_update(ref(item) for item in other)
+    def __iand__(self, other):
+        self.data.intersection_update(ref(item) for item in other)
+        return self
 
     def issubset(self, other):
         return self.data.issubset(ref(item) for item in other)
     __lt__ = issubset
 
+    def __le__(self, other):
+        return self.data <= set(ref(item) for item in other)
+
     def issuperset(self, other):
         return self.data.issuperset(ref(item) for item in other)
     __gt__ = issuperset
 
+    def __ge__(self, other):
+        return self.data >= set(ref(item) for item in other)
+
+    def __eq__(self, other):
+        return self.data == set(ref(item) for item in other)
+
     def symmetric_difference(self, other):
         return self._apply(other, self.data.symmetric_difference)
     __xor__ = symmetric_difference
 
     def symmetric_difference_update(self, other):
-        self._apply_mutate(other, self.data.symmetric_difference_update)
-    __ixor__ = symmetric_difference_update
+        if self is other:
+            self.data.clear()
+        else:
+            self.data.symmetric_difference_update(ref(item) for item in other)
+    def __ixor__(self, other):
+        if self is other:
+            self.data.clear()
+        else:
+            self.data.symmetric_difference_update(ref(item) for item in other)
+        return self
 
     def union(self, other):
         return self._apply(other, self.data.union)
     __or__ = union
+
+    def isdisjoint(self, other):
+        return len(self.intersection(other)) == 0
diff --git a/Lib/test/test_weakset.py b/Lib/test/test_weakset.py
new file mode 100644
index 0000000..22ac9af
--- /dev/null
+++ b/Lib/test/test_weakset.py
@@ -0,0 +1,311 @@
+import unittest
+from test import test_support
+from weakref import proxy, ref, WeakSet
+import operator
+import copy
+import string
+import os
+from random import randrange, shuffle
+import sys
+import warnings
+import collections
+from collections import UserString as ustr
+
+
+class Foo:
+    pass
+
+
+class TestWeakSet(unittest.TestCase):
+
+    def setUp(self):
+        # need to keep references to them
+        self.items = [ustr(c) for c in ('a', 'b', 'c')]
+        self.items2 = [ustr(c) for c in ('x', 'y', 'z')]
+        self.letters = [ustr(c) for c in string.ascii_letters]
+        self.s = WeakSet(self.items)
+        self.d = dict.fromkeys(self.items)
+        self.obj = ustr('F')
+        self.fs = WeakSet([self.obj])
+
+    def test_methods(self):
+        weaksetmethods = dir(WeakSet)
+        for method in dir(set):
+            if method.startswith('_'):
+                continue
+            self.assert_(method in weaksetmethods)
+
+    def test_new_or_init(self):
+        self.assertRaises(TypeError, WeakSet, [], 2)
+
+    def test_len(self):
+        self.assertEqual(len(self.s), len(self.d))
+        self.assertEqual(len(self.fs), 1)
+        del self.obj
+        self.assertEqual(len(self.fs), 0)
+
+    def test_contains(self):
+        for c in self.letters:
+            self.assertEqual(c in self.s, c in self.d)
+        self.assertRaises(TypeError, self.s.__contains__, [[]])
+        self.assert_(self.obj in self.fs)
+        del self.obj
+        self.assert_(ustr('F') not in self.fs)
+
+    def test_union(self):
+        u = self.s.union(self.items2)
+        for c in self.letters:
+            self.assertEqual(c in u, c in self.d or c in self.items2)
+        self.assertEqual(self.s, WeakSet(self.items))
+        self.assertEqual(type(u), WeakSet)
+        self.assertRaises(TypeError, self.s.union, [[]])
+        for C in set, frozenset, dict.fromkeys, list, tuple:
+            x = WeakSet(self.items + self.items2)
+            c = C(self.items2)
+            self.assertEqual(self.s.union(c), x)
+
+    def test_or(self):
+        i = self.s.union(self.items2)
+        self.assertEqual(self.s | set(self.items2), i)
+        self.assertEqual(self.s | frozenset(self.items2), i)
+
+    def test_intersection(self):
+        i = self.s.intersection(self.items2)
+        for c in self.letters:
+            self.assertEqual(c in i, c in self.d and c in self.items2)
+        self.assertEqual(self.s, WeakSet(self.items))
+        self.assertEqual(type(i), WeakSet)
+        for C in set, frozenset, dict.fromkeys, list, tuple:
+            x = WeakSet([])
+            self.assertEqual(self.s.intersection(C(self.items2)), x)
+
+    def test_isdisjoint(self):
+        self.assert_(self.s.isdisjoint(WeakSet(self.items2)))
+        self.assert_(not self.s.isdisjoint(WeakSet(self.letters)))
+
+    def test_and(self):
+        i = self.s.intersection(self.items2)
+        self.assertEqual(self.s & set(self.items2), i)
+        self.assertEqual(self.s & frozenset(self.items2), i)
+
+    def test_difference(self):
+        i = self.s.difference(self.items2)
+        for c in self.letters:
+            self.assertEqual(c in i, c in self.d and c not in self.items2)
+        self.assertEqual(self.s, WeakSet(self.items))
+        self.assertEqual(type(i), WeakSet)
+        self.assertRaises(TypeError, self.s.difference, [[]])
+
+    def test_sub(self):
+        i = self.s.difference(self.items2)
+        self.assertEqual(self.s - set(self.items2), i)
+        self.assertEqual(self.s - frozenset(self.items2), i)
+
+    def test_symmetric_difference(self):
+        i = self.s.symmetric_difference(self.items2)
+        for c in self.letters:
+            self.assertEqual(c in i, (c in self.d) ^ (c in self.items2))
+        self.assertEqual(self.s, WeakSet(self.items))
+        self.assertEqual(type(i), WeakSet)
+        self.assertRaises(TypeError, self.s.symmetric_difference, [[]])
+
+    def test_xor(self):
+        i = self.s.symmetric_difference(self.items2)
+        self.assertEqual(self.s ^ set(self.items2), i)
+        self.assertEqual(self.s ^ frozenset(self.items2), i)
+
+    def test_sub_and_super(self):
+        pl, ql, rl = map(lambda s: [ustr(c) for c in s], ['ab', 'abcde', 'def'])
+        p, q, r = map(WeakSet, (pl, ql, rl))
+        self.assert_(p < q)
+        self.assert_(p <= q)
+        self.assert_(q <= q)
+        self.assert_(q > p)
+        self.assert_(q >= p)
+        self.failIf(q < r)
+        self.failIf(q <= r)
+        self.failIf(q > r)
+        self.failIf(q >= r)
+        self.assert_(set('a').issubset('abc'))
+        self.assert_(set('abc').issuperset('a'))
+        self.failIf(set('a').issubset('cbs'))
+        self.failIf(set('cbs').issuperset('a'))
+
+    def test_gc(self):
+        # Create a nest of cycles to exercise overall ref count check
+        class A:
+            pass
+        s = set(A() for i in range(1000))
+        for elem in s:
+            elem.cycle = s
+            elem.sub = elem
+            elem.set = set([elem])
+
+    def test_subclass_with_custom_hash(self):
+        # Bug #1257731
+        class H(WeakSet):
+            def __hash__(self):
+                return int(id(self) & 0x7fffffff)
+        s=H()
+        f=set()
+        f.add(s)
+        self.assert_(s in f)
+        f.remove(s)
+        f.add(s)
+        f.discard(s)
+
+    def test_init(self):
+        s = WeakSet()
+        s.__init__(self.items)
+        self.assertEqual(s, self.s)
+        s.__init__(self.items2)
+        self.assertEqual(s, WeakSet(self.items2))
+        self.assertRaises(TypeError, s.__init__, s, 2);
+        self.assertRaises(TypeError, s.__init__, 1);
+
+    def test_constructor_identity(self):
+        s = WeakSet(self.items)
+        t = WeakSet(s)
+        self.assertNotEqual(id(s), id(t))
+
+    def test_set_literal(self):
+        s = set([1,2,3])
+        t = {1,2,3}
+        self.assertEqual(s, t)
+
+    def test_hash(self):
+        self.assertRaises(TypeError, hash, self.s)
+
+    def test_clear(self):
+        self.s.clear()
+        self.assertEqual(self.s, set())
+        self.assertEqual(len(self.s), 0)
+
+    def test_copy(self):
+        dup = self.s.copy()
+        self.assertEqual(self.s, dup)
+        self.assertNotEqual(id(self.s), id(dup))
+
+    def test_add(self):
+        x = ustr('Q')
+        self.s.add(x)
+        self.assert_(x in self.s)
+        dup = self.s.copy()
+        self.s.add(x)
+        self.assertEqual(self.s, dup)
+        self.assertRaises(TypeError, self.s.add, [])
+        self.fs.add(Foo())
+        self.assert_(len(self.fs) == 1)
+        self.fs.add(self.obj)
+        self.assert_(len(self.fs) == 1)
+
+    def test_remove(self):
+        x = ustr('a')
+        self.s.remove(x)
+        self.assert_(x not in self.s)
+        self.assertRaises(KeyError, self.s.remove, x)
+        self.assertRaises(TypeError, self.s.remove, [])
+
+    def test_discard(self):
+        a, q = ustr('a'), ustr('Q')
+        self.s.discard(a)
+        self.assert_(a not in self.s)
+        self.s.discard(q)
+        self.assertRaises(TypeError, self.s.discard, [])
+
+    def test_pop(self):
+        for i in range(len(self.s)):
+            elem = self.s.pop()
+            self.assert_(elem not in self.s)
+        self.assertRaises(KeyError, self.s.pop)
+
+    def test_update(self):
+        retval = self.s.update(self.items2)
+        self.assertEqual(retval, None)
+        for c in (self.items + self.items2):
+            self.assert_(c in self.s)
+        self.assertRaises(TypeError, self.s.update, [[]])
+
+    def test_update_set(self):
+        self.s.update(set(self.items2))
+        for c in (self.items + self.items2):
+            self.assert_(c in self.s)
+
+    def test_ior(self):
+        self.s |= set(self.items2)
+        for c in (self.items + self.items2):
+            self.assert_(c in self.s)
+
+    def test_intersection_update(self):
+        retval = self.s.intersection_update(self.items2)
+        self.assertEqual(retval, None)
+        for c in (self.items + self.items2):
+            if c in self.items2 and c in self.items:
+                self.assert_(c in self.s)
+            else:
+                self.assert_(c not in self.s)
+        self.assertRaises(TypeError, self.s.intersection_update, [[]])
+
+    def test_iand(self):
+        self.s &= set(self.items2)
+        for c in (self.items + self.items2):
+            if c in self.items2 and c in self.items:
+                self.assert_(c in self.s)
+            else:
+                self.assert_(c not in self.s)
+
+    def test_difference_update(self):
+        retval = self.s.difference_update(self.items2)
+        self.assertEqual(retval, None)
+        for c in (self.items + self.items2):
+            if c in self.items and c not in self.items2:
+                self.assert_(c in self.s)
+            else:
+                self.assert_(c not in self.s)
+        self.assertRaises(TypeError, self.s.difference_update, [[]])
+        self.assertRaises(TypeError, self.s.symmetric_difference_update, [[]])
+
+    def test_isub(self):
+        self.s -= set(self.items2)
+        for c in (self.items + self.items2):
+            if c in self.items and c not in self.items2:
+                self.assert_(c in self.s)
+            else:
+                self.assert_(c not in self.s)
+
+    def test_symmetric_difference_update(self):
+        retval = self.s.symmetric_difference_update(self.items2)
+        self.assertEqual(retval, None)
+        for c in (self.items + self.items2):
+            if (c in self.items) ^ (c in self.items2):
+                self.assert_(c in self.s)
+            else:
+                self.assert_(c not in self.s)
+        self.assertRaises(TypeError, self.s.symmetric_difference_update, [[]])
+
+    def test_ixor(self):
+        self.s ^= set(self.items2)
+        for c in (self.items + self.items2):
+            if (c in self.items) ^ (c in self.items2):
+                self.assert_(c in self.s)
+            else:
+                self.assert_(c not in self.s)
+
+    def test_inplace_on_self(self):
+        t = self.s.copy()
+        t |= t
+        self.assertEqual(t, self.s)
+        t &= t
+        self.assertEqual(t, self.s)
+        t -= t
+        self.assertEqual(t, WeakSet())
+        t = self.s.copy()
+        t ^= t
+        self.assertEqual(t, WeakSet())
+
+
+def test_main(verbose=None):
+    test_support.run_unittest(TestWeakSet)
+
+if __name__ == "__main__":
+    test_main(verbose=True)