Lib/test/test_weakref.py

import sys
import unittest
import UserList
import weakref

from test import test_support


class C:
    def method(self):
        pass


class Callable:
    bar = None

    def __call__(self, x):
        self.bar = x


def create_function():
    def f(): pass
    return f

def create_bound_method():
    return C().method

def create_unbound_method():
    return C.method


class TestBase(unittest.TestCase):

    def setUp(self):
        self.cbcalled = 0

    def callback(self, ref):
        self.cbcalled += 1


class ReferencesTestCase(TestBase):

    def test_basic_ref(self):
        self.check_basic_ref(C)
        self.check_basic_ref(create_function)
        self.check_basic_ref(create_bound_method)
        self.check_basic_ref(create_unbound_method)

        # Just make sure the tp_repr handler doesn't raise an exception.
        # Live reference:
        o = C()
        wr = weakref.ref(o)
        `wr`
        # Dead reference:
        del o
        `wr`

    def test_basic_callback(self):
        self.check_basic_callback(C)
        self.check_basic_callback(create_function)
        self.check_basic_callback(create_bound_method)
        self.check_basic_callback(create_unbound_method)

    def test_multiple_callbacks(self):
        o = C()
        ref1 = weakref.ref(o, self.callback)
        ref2 = weakref.ref(o, self.callback)
        del o
        self.assert_(ref1() is None,
                     "expected reference to be invalidated")
        self.assert_(ref2() is None,
                     "expected reference to be invalidated")
        self.assert_(self.cbcalled == 2,
                     "callback not called the right number of times")

    def test_multiple_selfref_callbacks(self):
        # Make sure all references are invalidated before callbacks are called
        #
        # What's important here is that we're using the first
        # reference in the callback invoked on the second reference
        # (the most recently created ref is cleaned up first).  This
        # tests that all references to the object are invalidated
        # before any of the callbacks are invoked, so that we only
        # have one invocation of _weakref.c:cleanup_helper() active
        # for a particular object at a time.
        #
        def callback(object, self=self):
            self.ref()
        c = C()
        self.ref = weakref.ref(c, callback)
        ref1 = weakref.ref(c, callback)
        del c

    def test_proxy_ref(self):
        o = C()
        o.bar = 1
        ref1 = weakref.proxy(o, self.callback)
        ref2 = weakref.proxy(o, self.callback)
        del o

        def check(proxy):
            proxy.bar

        self.assertRaises(weakref.ReferenceError, check, ref1)
        self.assertRaises(weakref.ReferenceError, check, ref2)
        self.assert_(self.cbcalled == 2)

    def check_basic_ref(self, factory):
        o = factory()
        ref = weakref.ref(o)
        self.assert_(ref() is not None,
                     "weak reference to live object should be live")
        o2 = ref()
        self.assert_(o is o2,
                     "<ref>() should return original object if live")

    def check_basic_callback(self, factory):
        self.cbcalled = 0
        o = factory()
        ref = weakref.ref(o, self.callback)
        del o
        self.assert_(self.cbcalled == 1,
                     "callback did not properly set 'cbcalled'")
        self.assert_(ref() is None,
                     "ref2 should be dead after deleting object reference")

    def test_ref_reuse(self):
        o = C()
        ref1 = weakref.ref(o)
        # create a proxy to make sure that there's an intervening creation
        # between these two; it should make no difference
        proxy = weakref.proxy(o)
        ref2 = weakref.ref(o)
        self.assert_(ref1 is ref2,
                     "reference object w/out callback should be re-used")

        o = C()
        proxy = weakref.proxy(o)
        ref1 = weakref.ref(o)
        ref2 = weakref.ref(o)
        self.assert_(ref1 is ref2,
                     "reference object w/out callback should be re-used")
        self.assert_(weakref.getweakrefcount(o) == 2,
                     "wrong weak ref count for object")
        del proxy
        self.assert_(weakref.getweakrefcount(o) == 1,
                     "wrong weak ref count for object after deleting proxy")

    def test_proxy_reuse(self):
        o = C()
        proxy1 = weakref.proxy(o)
        ref = weakref.ref(o)
        proxy2 = weakref.proxy(o)
        self.assert_(proxy1 is proxy2,
                     "proxy object w/out callback should have been re-used")

    def test_basic_proxy(self):
        o = C()
        self.check_proxy(o, weakref.proxy(o))

        L = UserList.UserList()
        p = weakref.proxy(L)
        self.failIf(p, "proxy for empty UserList should be false")
        p.append(12)
        self.assertEqual(len(L), 1)
        self.failUnless(p, "proxy for non-empty UserList should be true")
        p[:] = [2, 3]
        self.assertEqual(len(L), 2)
        self.assertEqual(len(p), 2)
        self.failUnless(3 in p,
                        "proxy didn't support __contains__() properly")
        p[1] = 5
        self.assertEqual(L[1], 5)
        self.assertEqual(p[1], 5)
        L2 = UserList.UserList(L)
        p2 = weakref.proxy(L2)
        self.assertEqual(p, p2)
        ## self.assertEqual(`L2`, `p2`)
        L3 = UserList.UserList(range(10))
        p3 = weakref.proxy(L3)
        self.assertEqual(L3[:], p3[:])
        self.assertEqual(L3[5:], p3[5:])
        self.assertEqual(L3[:5], p3[:5])
        self.assertEqual(L3[2:5], p3[2:5])

    def test_callable_proxy(self):
        o = Callable()
        ref1 = weakref.proxy(o)

        self.check_proxy(o, ref1)

        self.assert_(type(ref1) is weakref.CallableProxyType,
                     "proxy is not of callable type")
        ref1('twinkies!')
        self.assert_(o.bar == 'twinkies!',
                     "call through proxy not passed through to original")
        ref1(x='Splat.')
        self.assert_(o.bar == 'Splat.',
                     "call through proxy not passed through to original")

        # expect due to too few args
        self.assertRaises(TypeError, ref1)

        # expect due to too many args
        self.assertRaises(TypeError, ref1, 1, 2, 3)

    def check_proxy(self, o, proxy):
        o.foo = 1
        self.assert_(proxy.foo == 1,
                     "proxy does not reflect attribute addition")
        o.foo = 2
        self.assert_(proxy.foo == 2,
                     "proxy does not reflect attribute modification")
        del o.foo
        self.assert_(not hasattr(proxy, 'foo'),
                     "proxy does not reflect attribute removal")

        proxy.foo = 1
        self.assert_(o.foo == 1,
                     "object does not reflect attribute addition via proxy")
        proxy.foo = 2
        self.assert_(
            o.foo == 2,
            "object does not reflect attribute modification via proxy")
        del proxy.foo
        self.assert_(not hasattr(o, 'foo'),
                     "object does not reflect attribute removal via proxy")

    def test_proxy_deletion(self):
        # Test clearing of SF bug #762891
        class Foo:
            result = None
            def __delitem__(self, accessor):
                self.result = accessor
        g = Foo()
        f = weakref.proxy(g)
        del f[0]
        self.assertEqual(f.result, 0)

    def test_getweakrefcount(self):
        o = C()
        ref1 = weakref.ref(o)
        ref2 = weakref.ref(o, self.callback)
        self.assert_(weakref.getweakrefcount(o) == 2,
                     "got wrong number of weak reference objects")

        proxy1 = weakref.proxy(o)
        proxy2 = weakref.proxy(o, self.callback)
        self.assert_(weakref.getweakrefcount(o) == 4,
                     "got wrong number of weak reference objects")

    def test_getweakrefs(self):
        o = C()
        ref1 = weakref.ref(o, self.callback)
        ref2 = weakref.ref(o, self.callback)
        del ref1
        self.assert_(weakref.getweakrefs(o) == [ref2],
                     "list of refs does not match")

        o = C()
        ref1 = weakref.ref(o, self.callback)
        ref2 = weakref.ref(o, self.callback)
        del ref2
        self.assert_(weakref.getweakrefs(o) == [ref1],
                     "list of refs does not match")

    def test_newstyle_number_ops(self):
        class F(float):
            pass
        f = F(2.0)
        p = weakref.proxy(f)
        self.assert_(p + 1.0 == 3.0)
        self.assert_(1.0 + p == 3.0)  # this used to SEGV

    def test_callbacks_protected(self):
        # Callbacks protected from already-set exceptions?
        # Regression test for SF bug #478534.
        class BogusError(Exception):
            pass
        data = {}
        def remove(k):
            del data[k]
        def encapsulate():
            f = lambda : ()
            data[weakref.ref(f, remove)] = None
            raise BogusError
        try:
            encapsulate()
        except BogusError:
            pass
        else:
            self.fail("exception not properly restored")
        try:
            encapsulate()
        except BogusError:
            pass
        else:
            self.fail("exception not properly restored")

    def test_sf_bug_840829(self):
        # "weakref callbacks and gc corrupt memory"
        # subtype_dealloc erroneously exposed a new-style instance
        # already in the process of getting deallocated to gc,
        # causing double-deallocation if the instance had a weakref
        # callback that triggered gc.
        # If the bug exists, there probably won't be an obvious symptom
        # in a release build.  In a debug build, a segfault will occur
        # when the second attempt to remove the instance from the "list
        # of all objects" occurs.

        import gc

        class C(object):
            pass

        c = C()
        wr = weakref.ref(c, lambda ignore: gc.collect())
        del c

        # There endeth the first part.  It gets worse.
        del wr

        c1 = C()
        c1.i = C()
        wr = weakref.ref(c1.i, lambda ignore: gc.collect())

        c2 = C()
        c2.c1 = c1
        del c1  # still alive because c2 points to it

        # Now when subtype_dealloc gets called on c2, it's not enough just
        # that c2 is immune from gc while the weakref callbacks associated
        # with c2 execute (there are none in this 2nd half of the test, btw).
        # subtype_dealloc goes on to call the base classes' deallocs too,
        # so any gc triggered by weakref callbacks associated with anything
        # torn down by a base class dealloc can also trigger double
        # deallocation of c2.
        del c2

    def test_callback_in_cycle_1(self):
        import gc

        class J(object):
            pass

        class II(object):
            def acallback(self, ignore):
                self.J

        I = II()
        I.J = J
        I.wr = weakref.ref(J, I.acallback)

        # Now J and II are each in a self-cycle (as all new-style class
        # objects are, since their __mro__ points back to them).  I holds
        # both a weak reference (I.wr) and a strong reference (I.J) to class
        # J.  I is also in a cycle (I.wr points to a weakref that references
        # I.acallback).  When we del these three, they all become trash, but
        # the cycles prevent any of them from getting cleaned up immediately.
        # Instead they have to wait for cyclic gc to deduce that they're
        # trash.
        #
        # gc used to call tp_clear on all of them, and the order in which
        # it does that is pretty accidental.  The exact order in which we
        # built up these things manages to provoke gc into running tp_clear
        # in just the right order (I last).  Calling tp_clear on II leaves
        # behind an insane class object (its __mro__ becomes NULL).  Calling
        # tp_clear on J breaks its self-cycle, but J doesn't get deleted
        # just then because of the strong reference from I.J.  Calling
        # tp_clear on I starts to clear I's __dict__, and just happens to
        # clear I.J first -- I.wr is still intact.  That removes the last
        # reference to J, which triggers the weakref callback.  The callback
        # tries to do "self.J", and instances of new-style classes look up
        # attributes ("J") in the class dict first.  The class (II) wants to
        # search II.__mro__, but that's NULL.   The result was a segfault in
        # a release build, and an assert failure in a debug build.
        del I, J, II
        gc.collect()

    def test_callback_in_cycle_2(self):
        import gc

        # This is just like test_callback_in_cycle_1, except that II is an
        # old-style class.  The symptom is different then:  an instance of an
        # old-style class looks in its own __dict__ first.  'J' happens to
        # get cleared from I.__dict__ before 'wr', and 'J' was never in II's
        # __dict__, so the attribute isn't found.  The difference is that
        # the old-style II doesn't have a NULL __mro__ (it doesn't have any
        # __mro__), so no segfault occurs.  Instead it got:
        #    test_callback_in_cycle_2 (__main__.ReferencesTestCase) ...
        #    Exception exceptions.AttributeError:
        #   "II instance has no attribute 'J'" in <bound method II.acallback
        #       of <?.II instance at 0x00B9B4B8>> ignored

        class J(object):
            pass

        class II:
            def acallback(self, ignore):
                self.J

        I = II()
        I.J = J
        I.wr = weakref.ref(J, I.acallback)

        del I, J, II
        gc.collect()

    def test_callback_in_cycle_3(self):
        import gc

        # This one broke the first patch that fixed the last two.  In this
        # case, the objects reachable from the callback aren't also reachable
        # from the object (c1) *triggering* the callback:  you can get to
        # c1 from c2, but not vice-versa.  The result was that c2's __dict__
        # got tp_clear'ed by the time the c2.cb callback got invoked.

        class C:
            def cb(self, ignore):
                self.me
                self.c1
                self.wr

        c1, c2 = C(), C()

        c2.me = c2
        c2.c1 = c1
        c2.wr = weakref.ref(c1, c2.cb)

        del c1, c2
        gc.collect()

    def test_callback_in_cycle_4(self):
        import gc

        # Like test_callback_in_cycle_3, except c2 and c1 have different
        # classes.  c2's class (C) isn't reachable from c1 then, so protecting
        # objects reachable from the dying object (c1) isn't enough to stop
        # c2's class (C) from getting tp_clear'ed before c2.cb is invoked.
        # The result was a segfault (C.__mro__ was NULL when the callback
        # tried to look up self.me).

        class C(object):
            def cb(self, ignore):
                self.me
                self.c1
                self.wr

        class D:
            pass

        c1, c2 = D(), C()

        c2.me = c2
        c2.c1 = c1
        c2.wr = weakref.ref(c1, c2.cb)

        del c1, c2, C, D
        gc.collect()

    def test_callback_in_cycle_resurrection(self):
        import gc

        # Do something nasty in a weakref callback:  resurrect objects
        # from dead cycles.  For this to be attempted, the weakref and
        # its callback must also be part of the cyclic trash (else the
        # objects reachable via the callback couldn't be in cyclic trash
        # to begin with -- the callback would act like an external root).
        # But gc clears trash weakrefs with callbacks early now, which
        # disables the callbacks, so the callbacks shouldn't get called
        # at all (and so nothing actually gets resurrected).

        alist = []
        class C(object):
            def __init__(self, value):
                self.attribute = value

            def acallback(self, ignore):
                alist.append(self.c)

        c1, c2 = C(1), C(2)
        c1.c = c2
        c2.c = c1
        c1.wr = weakref.ref(c2, c1.acallback)
        c2.wr = weakref.ref(c1, c2.acallback)

        def C_went_away(ignore):
            alist.append("C went away")
        wr = weakref.ref(C, C_went_away)

        del c1, c2, C   # make them all trash
        self.assertEqual(alist, [])  # del isn't enough to reclaim anything

        gc.collect()
        # c1.wr and c2.wr were part of the cyclic trash, so should have
        # been cleared without their callbacks executing.  OTOH, the weakref
        # to C is bound to a function local (wr), and wasn't trash, so that
        # callback should have been invoked when C went away.
        self.assertEqual(alist, ["C went away"])
        # The remaining weakref should be dead now (its callback ran).
        self.assertEqual(wr(), None)

        del alist[:]
        gc.collect()
        self.assertEqual(alist, [])

    def test_callbacks_on_callback(self):
        import gc

        # Set up weakref callbacks *on* weakref callbacks.
        alist = []
        def safe_callback(ignore):
            alist.append("safe_callback called")

        class C(object):
            def cb(self, ignore):
                alist.append("cb called")

        c, d = C(), C()
        c.other = d
        d.other = c
        callback = c.cb
        c.wr = weakref.ref(d, callback)     # this won't trigger
        d.wr = weakref.ref(callback, d.cb)  # ditto
        external_wr = weakref.ref(callback, safe_callback)  # but this will
        self.assert_(external_wr() is callback)

        # The weakrefs attached to c and d should get cleared, so that
        # C.cb is never called.  But external_wr isn't part of the cyclic
        # trash, and no cyclic trash is reachable from it, so safe_callback
        # should get invoked when the bound method object callback (c.cb)
        # -- which is itself a callback, and also part of the cyclic trash --
        # gets reclaimed at the end of gc.

        del callback, c, d, C
        self.assertEqual(alist, [])  # del isn't enough to clean up cycles
        gc.collect()
        self.assertEqual(alist, ["safe_callback called"])
        self.assertEqual(external_wr(), None)

        del alist[:]
        gc.collect()
        self.assertEqual(alist, [])

class Object:
    def __init__(self, arg):
        self.arg = arg
    def __repr__(self):
        return "<Object %r>" % self.arg


class MappingTestCase(TestBase):

    COUNT = 10

    def test_weak_values(self):
        #
        #  This exercises d.copy(), d.items(), d[], del d[], len(d).
        #
        dict, objects = self.make_weak_valued_dict()
        for o in objects:
            self.assert_(weakref.getweakrefcount(o) == 1,
                         "wrong number of weak references to %r!" % o)
            self.assert_(o is dict[o.arg],
                         "wrong object returned by weak dict!")
        items1 = dict.items()
        items2 = dict.copy().items()
        items1.sort()
        items2.sort()
        self.assert_(items1 == items2,
                     "cloning of weak-valued dictionary did not work!")
        del items1, items2
        self.assert_(len(dict) == self.COUNT)
        del objects[0]
        self.assert_(len(dict) == (self.COUNT - 1),
                     "deleting object did not cause dictionary update")
        del objects, o
        self.assert_(len(dict) == 0,
                     "deleting the values did not clear the dictionary")
        # regression on SF bug #447152:
        dict = weakref.WeakValueDictionary()
        self.assertRaises(KeyError, dict.__getitem__, 1)
        dict[2] = C()
        self.assertRaises(KeyError, dict.__getitem__, 2)

    def test_weak_keys(self):
        #
        #  This exercises d.copy(), d.items(), d[] = v, d[], del d[],
        #  len(d), d.has_key().
        #
        dict, objects = self.make_weak_keyed_dict()
        for o in objects:
            self.assert_(weakref.getweakrefcount(o) == 1,
                         "wrong number of weak references to %r!" % o)
            self.assert_(o.arg is dict[o],
                         "wrong object returned by weak dict!")
        items1 = dict.items()
        items2 = dict.copy().items()
        self.assert_(set(items1) == set(items2),
                     "cloning of weak-keyed dictionary did not work!")
        del items1, items2
        self.assert_(len(dict) == self.COUNT)
        del objects[0]
        self.assert_(len(dict) == (self.COUNT - 1),
                     "deleting object did not cause dictionary update")
        del objects, o
        self.assert_(len(dict) == 0,
                     "deleting the keys did not clear the dictionary")
        o = Object(42)
        dict[o] = "What is the meaning of the universe?"
        self.assert_(dict.has_key(o))
        self.assert_(not dict.has_key(34))

    def test_weak_keyed_iters(self):
        dict, objects = self.make_weak_keyed_dict()
        self.check_iters(dict)

    def test_weak_valued_iters(self):
        dict, objects = self.make_weak_valued_dict()
        self.check_iters(dict)

    def check_iters(self, dict):
        # item iterator:
        items = dict.items()
        for item in dict.iteritems():
            items.remove(item)
        self.assert_(len(items) == 0, "iteritems() did not touch all items")

        # key iterator, via __iter__():
        keys = dict.keys()
        for k in dict:
            keys.remove(k)
        self.assert_(len(keys) == 0, "__iter__() did not touch all keys")

        # key iterator, via iterkeys():
        keys = dict.keys()
        for k in dict.iterkeys():
            keys.remove(k)
        self.assert_(len(keys) == 0, "iterkeys() did not touch all keys")

        # value iterator:
        values = dict.values()
        for v in dict.itervalues():
            values.remove(v)
        self.assert_(len(values) == 0,
                     "itervalues() did not touch all values")

    def test_make_weak_keyed_dict_from_dict(self):
        o = Object(3)
        dict = weakref.WeakKeyDictionary({o:364})
        self.assert_(dict[o] == 364)

    def test_make_weak_keyed_dict_from_weak_keyed_dict(self):
        o = Object(3)
        dict = weakref.WeakKeyDictionary({o:364})
        dict2 = weakref.WeakKeyDictionary(dict)
        self.assert_(dict[o] == 364)

    def make_weak_keyed_dict(self):
        dict = weakref.WeakKeyDictionary()
        objects = map(Object, range(self.COUNT))
        for o in objects:
            dict[o] = o.arg
        return dict, objects

    def make_weak_valued_dict(self):
        dict = weakref.WeakValueDictionary()
        objects = map(Object, range(self.COUNT))
        for o in objects:
            dict[o.arg] = o
        return dict, objects

    def check_popitem(self, klass, key1, value1, key2, value2):
        weakdict = klass()
        weakdict[key1] = value1
        weakdict[key2] = value2
        self.assert_(len(weakdict) == 2)
        k, v = weakdict.popitem()
        self.assert_(len(weakdict) == 1)
        if k is key1:
            self.assert_(v is value1)
        else:
            self.assert_(v is value2)
        k, v = weakdict.popitem()
        self.assert_(len(weakdict) == 0)
        if k is key1:
            self.assert_(v is value1)
        else:
            self.assert_(v is value2)

    def test_weak_valued_dict_popitem(self):
        self.check_popitem(weakref.WeakValueDictionary,
                           "key1", C(), "key2", C())

    def test_weak_keyed_dict_popitem(self):
        self.check_popitem(weakref.WeakKeyDictionary,
                           C(), "value 1", C(), "value 2")

    def check_setdefault(self, klass, key, value1, value2):
        self.assert_(value1 is not value2,
                     "invalid test"
                     " -- value parameters must be distinct objects")
        weakdict = klass()
        o = weakdict.setdefault(key, value1)
        self.assert_(o is value1)
        self.assert_(weakdict.has_key(key))
        self.assert_(weakdict.get(key) is value1)
        self.assert_(weakdict[key] is value1)

        o = weakdict.setdefault(key, value2)
        self.assert_(o is value1)
        self.assert_(weakdict.has_key(key))
        self.assert_(weakdict.get(key) is value1)
        self.assert_(weakdict[key] is value1)

    def test_weak_valued_dict_setdefault(self):
        self.check_setdefault(weakref.WeakValueDictionary,
                              "key", C(), C())

    def test_weak_keyed_dict_setdefault(self):
        self.check_setdefault(weakref.WeakKeyDictionary,
                              C(), "value 1", "value 2")

    def check_update(self, klass, dict):
        #
        #  This exercises d.update(), len(d), d.keys(), d.has_key(),
        #  d.get(), d[].
        #
        weakdict = klass()
        weakdict.update(dict)
        self.assert_(len(weakdict) == len(dict))
        for k in weakdict.keys():
            self.assert_(dict.has_key(k),
                         "mysterious new key appeared in weak dict")
            v = dict.get(k)
            self.assert_(v is weakdict[k])
            self.assert_(v is weakdict.get(k))
        for k in dict.keys():
            self.assert_(weakdict.has_key(k),
                         "original key disappeared in weak dict")
            v = dict[k]
            self.assert_(v is weakdict[k])
            self.assert_(v is weakdict.get(k))

    def test_weak_valued_dict_update(self):
        self.check_update(weakref.WeakValueDictionary,
                          {1: C(), 'a': C(), C(): C()})

    def test_weak_keyed_dict_update(self):
        self.check_update(weakref.WeakKeyDictionary,
                          {C(): 1, C(): 2, C(): 3})

    def test_weak_keyed_delitem(self):
        d = weakref.WeakKeyDictionary()
        o1 = Object('1')
        o2 = Object('2')
        d[o1] = 'something'
        d[o2] = 'something'
        self.assert_(len(d) == 2)
        del d[o1]
        self.assert_(len(d) == 1)
        self.assert_(d.keys() == [o2])

    def test_weak_valued_delitem(self):
        d = weakref.WeakValueDictionary()
        o1 = Object('1')
        o2 = Object('2')
        d['something'] = o1
        d['something else'] = o2
        self.assert_(len(d) == 2)
        del d['something']
        self.assert_(len(d) == 1)
        self.assert_(d.items() == [('something else', o2)])

    def test_weak_keyed_bad_delitem(self):
        d = weakref.WeakKeyDictionary()
        o = Object('1')
        # An attempt to delete an object that isn't there should raise
        # KeyError.  It didn't before 2.3.
        self.assertRaises(KeyError, d.__delitem__, o)
        self.assertRaises(KeyError, d.__getitem__, o)

        # If a key isn't of a weakly referencable type, __getitem__ and
        # __setitem__ raise TypeError.  __delitem__ should too.
        self.assertRaises(TypeError, d.__delitem__,  13)
        self.assertRaises(TypeError, d.__getitem__,  13)
        self.assertRaises(TypeError, d.__setitem__,  13, 13)

    def test_weak_keyed_cascading_deletes(self):
        # SF bug 742860.  For some reason, before 2.3 __delitem__ iterated
        # over the keys via self.data.iterkeys().  If things vanished from
        # the dict during this (or got added), that caused a RuntimeError.

        d = weakref.WeakKeyDictionary()
        mutate = False

        class C(object):
            def __init__(self, i):
                self.value = i
            def __hash__(self):
                return hash(self.value)
            def __eq__(self, other):
                if mutate:
                    # Side effect that mutates the dict, by removing the
                    # last strong reference to a key.
                    del objs[-1]
                return self.value == other.value

        objs = [C(i) for i in range(4)]
        for o in objs:
            d[o] = o.value
        del o   # now the only strong references to keys are in objs
        # Find the order in which iterkeys sees the keys.
        objs = d.keys()
        # Reverse it, so that the iteration implementation of __delitem__
        # has to keep looping to find the first object we delete.
        objs.reverse()

        # Turn on mutation in C.__eq__.  The first time thru the loop,
        # under the iterkeys() business the first comparison will delete
        # the last item iterkeys() would see, and that causes a
        #     RuntimeError: dictionary changed size during iteration
        # when the iterkeys() loop goes around to try comparing the next
        # key.  After this was fixed, it just deletes the last object *our*
        # "for o in obj" loop would have gotten to.
        mutate = True
        count = 0
        for o in objs:
            count += 1
            del d[o]
        self.assertEqual(len(d), 0)
        self.assertEqual(count, 2)

from test_userdict import TestMappingProtocol

class WeakValueDictionaryTestCase(TestMappingProtocol):
    """Check that WeakValueDictionary conforms to the mapping protocol"""
    __ref = {"key1":Object(1), "key2":Object(2), "key3":Object(3)}
    _tested_class = weakref.WeakValueDictionary
    def _reference(self):
        return self.__ref.copy()

class WeakKeyDictionaryTestCase(TestMappingProtocol):
    """Check that WeakKeyDictionary conforms to the mapping protocol"""
    __ref = {Object("key1"):1, Object("key2"):2, Object("key3"):3}
    _tested_class = weakref.WeakKeyDictionary
    def _reference(self):
        return self.__ref.copy()

def test_main():
    test_support.run_unittest(
        ReferencesTestCase,
        MappingTestCase,
        WeakValueDictionaryTestCase,
        WeakKeyDictionaryTestCase,
        )


if __name__ == "__main__":
    test_main()