diff --git a/Doc/c-api/type.rst b/Doc/c-api/type.rst
index 01a94bbed44..d1d4e456231 100644
--- a/Doc/c-api/type.rst
+++ b/Doc/c-api/type.rst
@@ -33,6 +33,13 @@ Type Objects
    standard type object.  Return false in all other cases.
 
 
+.. cfunction:: unsigned int PyType_ClearCache(void)
+
+   Clears the internal lookup cache. Return the current version tag.
+
+   .. versionadded:: 2.6
+
+
 .. cfunction:: int PyType_HasFeature(PyObject *o, int feature)
 
    Return true if the type object *o* sets the feature *feature*.  Type features
diff --git a/Doc/conf.py b/Doc/conf.py
index 83596748518..3c33f98d6c6 100644
--- a/Doc/conf.py
+++ b/Doc/conf.py
@@ -13,6 +13,8 @@ sys.path.append('tools/sphinxext')
 # General configuration
 # ---------------------
 
+extensions = ['sphinx.addons.refcounting']
+
 # General substitutions.
 project = 'Python'
 copyright = '1990-%s, Python Software Foundation' % time.strftime('%Y')
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 5718f7b02f8..5fdff4429c3 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -54,6 +54,13 @@ always available.
    A string containing the copyright pertaining to the Python interpreter.
 
 
+.. function:: _cleartypecache()
+
+   Clear the internal type lookup cache.
+
+   .. versionadded:: 2.6
+
+
 .. function:: _current_frames()
 
    Return a dictionary mapping each thread's identifier to the topmost stack frame
diff --git a/Include/object.h b/Include/object.h
index 90a3354f25a..5fc8ccb6aef 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -428,6 +428,7 @@ PyAPI_FUNC(PyObject *) PyType_GenericAlloc(PyTypeObject *, Py_ssize_t);
 PyAPI_FUNC(PyObject *) PyType_GenericNew(PyTypeObject *,
 					       PyObject *, PyObject *);
 PyAPI_FUNC(PyObject *) _PyType_Lookup(PyTypeObject *, PyObject *);
+PyAPI_FUNC(unsigned int) PyType_ClearCache(void);
 
 /* Generic operations on objects */
 PyAPI_FUNC(int) PyObject_Print(PyObject *, FILE *, int);
diff --git a/Lib/pydoc.py b/Lib/pydoc.py
index 755d51a6a95..0fdbb900a82 100755
--- a/Lib/pydoc.py
+++ b/Lib/pydoc.py
@@ -1203,7 +1203,6 @@ class TextDoc(Doc):
             else:
                 tag = "inherited from %s" % classname(thisclass,
                                                       object.__module__)
-            filter(lambda t: not t[0].startswith('_'), attrs)
 
             # Sort attrs by name.
             attrs.sort()
diff --git a/Lib/rational.py b/Lib/rational.py
index da75ab1f267..8de8f230ad7 100755
--- a/Lib/rational.py
+++ b/Lib/rational.py
@@ -24,60 +24,6 @@ def gcd(a, b):
     return a
 
 
-def _binary_float_to_ratio(x):
-    """x -> (top, bot), a pair of ints s.t. x = top/bot.
-
-    The conversion is done exactly, without rounding.
-    bot > 0 guaranteed.
-    Some form of binary fp is assumed.
-    Pass NaNs or infinities at your own risk.
-
-    >>> _binary_float_to_ratio(10.0)
-    (10, 1)
-    >>> _binary_float_to_ratio(0.0)
-    (0, 1)
-    >>> _binary_float_to_ratio(-.25)
-    (-1, 4)
-    """
-    # XXX Move this to floatobject.c with a name like
-    # float.as_integer_ratio()
-
-    if x == 0:
-        return 0, 1
-    f, e = math.frexp(x)
-    signbit = 1
-    if f < 0:
-        f = -f
-        signbit = -1
-    assert 0.5 <= f < 1.0
-    # x = signbit * f * 2**e exactly
-
-    # Suck up CHUNK bits at a time; 28 is enough so that we suck
-    # up all bits in 2 iterations for all known binary double-
-    # precision formats, and small enough to fit in an int.
-    CHUNK = 28
-    top = 0
-    # invariant: x = signbit * (top + f) * 2**e exactly
-    while f:
-        f = math.ldexp(f, CHUNK)
-        digit = trunc(f)
-        assert digit >> CHUNK == 0
-        top = (top << CHUNK) | digit
-        f = f - digit
-        assert 0.0 <= f < 1.0
-        e = e - CHUNK
-    assert top
-
-    # Add in the sign bit.
-    top = signbit * top
-
-    # now x = top * 2**e exactly; fold in 2**e
-    if e>0:
-        return (top * 2**e, 1)
-    else:
-        return (top, 2 ** -e)
-
-
 _RATIONAL_FORMAT = re.compile(
     r'^\s*(?P<sign>[-+]?)(?P<num>\d+)'
     r'(?:/(?P<denom>\d+)|\.(?P<decimal>\d+))?\s*$')
@@ -162,7 +108,7 @@ class Rational(RationalAbc):
                             (cls.__name__, f, type(f).__name__))
         if math.isnan(f) or math.isinf(f):
             raise TypeError("Cannot convert %r to %s." % (f, cls.__name__))
-        return cls(*_binary_float_to_ratio(f))
+        return cls(*f.as_integer_ratio())
 
     @classmethod
     def from_decimal(cls, dec):
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 790d769c97a..5934e6bb976 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -752,6 +752,9 @@ def dash_R_cleanup(fs, ps, pic, abcs):
     sys.path_importer_cache.clear()
     sys.path_importer_cache.update(pic)
 
+    # clear type cache
+    sys._cleartypecache()
+
     # Clear ABC registries, restoring previously saved ABC registries.
     for abc in [getattr(_abcoll, a) for a in _abcoll.__all__]:
         if not issubclass(abc, _Abstract):
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index e6ded8103b0..92c1d00dfcf 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -5,7 +5,7 @@ from test.test_support import fcmp, TESTFN, unlink,  run_unittest, \
                               run_with_locale
 from operator import neg
 
-import sys, warnings, random, UserDict, io
+import sys, warnings, random, UserDict, io, rational
 warnings.filterwarnings("ignore", "hex../oct.. of negative int",
                         FutureWarning, __name__)
 warnings.filterwarnings("ignore", "integer argument expected",
@@ -592,6 +592,25 @@ class BuiltinTest(unittest.TestCase):
         # make sure we can take a subclass of str as a format spec
         self.assertEqual(format(0, C('10')), '         0')
 
+    def test_floatasratio(self):
+        R = rational.Rational
+        self.assertEqual(R(0, 1),
+                         R(*float(0.0).as_integer_ratio()))
+        self.assertEqual(R(5, 2),
+                         R(*float(2.5).as_integer_ratio()))
+        self.assertEqual(R(1, 2),
+                         R(*float(0.5).as_integer_ratio()))
+        self.assertEqual(R(4728779608739021, 2251799813685248),
+                         R(*float(2.1).as_integer_ratio()))
+        self.assertEqual(R(-4728779608739021, 2251799813685248),
+                         R(*float(-2.1).as_integer_ratio()))
+        self.assertEqual(R(-2100, 1),
+                         R(*float(-2100.0).as_integer_ratio()))
+
+        self.assertRaises(OverflowError, float('inf').as_integer_ratio)
+        self.assertRaises(OverflowError, float('-inf').as_integer_ratio)
+        self.assertRaises(ValueError, float('nan').as_integer_ratio)
+
     def test_getattr(self):
         import sys
         self.assert_(getattr(sys, 'stdout') is sys.stdout)
diff --git a/Lib/test/test_resource.py b/Lib/test/test_resource.py
index 43ff3728c90..86440b50b2c 100644
--- a/Lib/test/test_resource.py
+++ b/Lib/test/test_resource.py
@@ -56,13 +56,12 @@ class ResourceTest(unittest.TestCase):
                         f.flush()
                         # On some systems (e.g., Ubuntu on hppa) the flush()
                         # doesn't always cause the exception, but the close()
-                        # does eventually.  Try closing several times in
+                        # does eventually.  Try flushing several times in
                         # an attempt to ensure the file is really synced and
                         # the exception raised.
                         for i in range(5):
                             time.sleep(.1)
                             f.flush()
-                            f.close()
                     except IOError:
                         if not limit_set:
                             raise
diff --git a/Lib/test/test_xmlrpc.py b/Lib/test/test_xmlrpc.py
index 28cbf0c8738..092be51a71c 100644
--- a/Lib/test/test_xmlrpc.py
+++ b/Lib/test/test_xmlrpc.py
@@ -312,9 +312,16 @@ def is_unavailable_exception(e):
        given by operations on non-blocking sockets.'''
 
     # sometimes we get a -1 error code and/or empty headers
-    if e.errcode == -1 or e.headers is None:
-        return True
+    try:
+        if e.errcode == -1 or e.headers is None:
+            return True
+        exc_mess = e.headers.get('X-exception')
+    except AttributeError:
+        # Ignore socket.errors here.
+        exc_mess = str(e)
 
+    if exc_mess and 'temporarily unavailable' in exc_mess.lower():
+        return True
 
 class SimpleServerTestCase(unittest.TestCase):
     def setUp(self):
@@ -349,7 +356,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
     # [ch] The test 404 is causing lots of false alarms.
     def XXXtest_404(self):
@@ -375,7 +382,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
 
     def test_introspection2(self):
@@ -388,7 +395,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
     def test_introspection3(self):
         try:
@@ -400,7 +407,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
     def test_introspection4(self):
         # the SimpleXMLRPCServer doesn't support signatures, but
@@ -413,7 +420,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
     def test_multicall(self):
         try:
@@ -430,7 +437,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
     def test_non_existing_multicall(self):
         try:
@@ -451,7 +458,7 @@ class SimpleServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
 # This is a contrived way to make a failure occur on the server side
 # in order to test the _send_traceback_header flag on the server
@@ -498,7 +505,7 @@ class FailingServerTestCase(unittest.TestCase):
             # ignore failures due to non-blocking socket 'unavailable' errors
             if not is_unavailable_exception(e):
                 # protocol error; provide additional information in test output
-                self.fail("%s\n%s" % (e, e.headers))
+                self.fail("%s\n%s" % (e, getattr(e, "headers", "")))
 
     def test_fail_no_info(self):
         # use the broken message class
@@ -509,7 +516,7 @@ class FailingServerTestCase(unittest.TestCase):
             p.pow(6,8)
         except (xmlrpclib.ProtocolError, socket.error) as e:
             # ignore failures due to non-blocking socket 'unavailable' errors
-            if not is_unavailable_exception(e):
+            if not is_unavailable_exception(e) and hasattr(e, "headers"):
                 # The two server-side error headers shouldn't be sent back in this case
                 self.assertTrue(e.headers.get("X-exception") is None)
                 self.assertTrue(e.headers.get("X-traceback") is None)
@@ -529,7 +536,7 @@ class FailingServerTestCase(unittest.TestCase):
             p.pow(6,8)
         except (xmlrpclib.ProtocolError, socket.error) as e:
             # ignore failures due to non-blocking socket 'unavailable' errors
-            if not is_unavailable_exception(e):
+            if not is_unavailable_exception(e) and hasattr(e, "headers"):
                 # We should get error info in the response
                 expected_err = "invalid literal for int() with base 10: 'I am broken'"
                 self.assertEqual(e.headers.get("x-exception"), expected_err)
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 859abf00a05..8ef3261c6ad 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -1073,6 +1073,163 @@ float_float(PyObject *v)
 	return v;
 }
 
+static PyObject *
+float_as_integer_ratio(PyObject *v)
+{
+	double self;
+	double float_part;
+	int exponent;
+	int is_negative;
+	const int chunk_size = 28;
+	PyObject *prev;
+	PyObject *py_chunk = NULL;
+	PyObject *py_exponent = NULL;
+	PyObject *numerator = NULL;
+	PyObject *denominator = NULL;
+	PyObject *result_pair = NULL;
+	PyNumberMethods *long_methods;
+
+#define INPLACE_UPDATE(obj, call) \
+	prev = obj; \
+	obj = call; \
+	Py_DECREF(prev); \
+
+	CONVERT_TO_DOUBLE(v, self);
+
+	if (Py_IS_INFINITY(self)) {
+	  PyErr_SetString(PyExc_OverflowError,
+			  "Cannot pass infinity to float.as_integer_ratio.");
+	  return NULL;
+	}
+#ifdef Py_NAN
+	if (Py_IS_NAN(self)) {
+	  PyErr_SetString(PyExc_ValueError,
+			  "Cannot pass nan to float.as_integer_ratio.");
+	  return NULL;
+	}
+#endif
+
+	if (self == 0) {
+		numerator = PyLong_FromLong(0);
+		if (numerator == NULL) goto error;
+		denominator = PyLong_FromLong(1);
+		if (denominator == NULL) goto error;
+		result_pair = PyTuple_Pack(2, numerator, denominator);
+		/* Hand ownership over to the tuple. If the tuple
+		   wasn't created successfully, we want to delete the
+		   ints anyway. */
+		Py_DECREF(numerator);
+		Py_DECREF(denominator);
+		return result_pair;
+	}
+
+	/* XXX: Could perhaps handle FLT_RADIX!=2 by using ilogb and
+	   scalbn, but those may not be in C89. */
+	PyFPE_START_PROTECT("as_integer_ratio", goto error);
+	float_part = frexp(self, &exponent);
+	is_negative = 0;
+	if (float_part < 0) {
+		float_part = -float_part;
+		is_negative = 1;
+		/* 0.5 <= float_part < 1.0 */
+	}
+	PyFPE_END_PROTECT(float_part);
+	/* abs(self) == float_part * 2**exponent exactly */
+
+	/* Suck up chunk_size bits at a time; 28 is enough so that we
+	   suck up all bits in 2 iterations for all known binary
+	   double-precision formats, and small enough to fit in a
+	   long. */
+	numerator = PyLong_FromLong(0);
+	if (numerator == NULL) goto error;
+
+	long_methods = PyLong_Type.tp_as_number;
+
+	py_chunk = PyLong_FromLong(chunk_size);
+	if (py_chunk == NULL) goto error;
+
+	while (float_part != 0) {
+		/* invariant: abs(self) ==
+		   (numerator + float_part) * 2**exponent exactly */
+		long digit;
+		PyObject *py_digit;
+
+		PyFPE_START_PROTECT("as_integer_ratio", goto error);
+		/* Pull chunk_size bits out of float_part, into digits. */
+		float_part = ldexp(float_part, chunk_size);
+		digit = (long)float_part;
+		float_part -= digit;
+                /* 0 <= float_part < 1 */
+		exponent -= chunk_size;
+		PyFPE_END_PROTECT(float_part);
+
+		/* Shift digits into numerator. */
+		// numerator <<= chunk_size
+		INPLACE_UPDATE(numerator,
+			       long_methods->nb_lshift(numerator, py_chunk));
+		if (numerator == NULL) goto error;
+
+		// numerator |= digit
+		py_digit = PyLong_FromLong(digit);
+		if (py_digit == NULL) goto error;
+		INPLACE_UPDATE(numerator,
+			       long_methods->nb_or(numerator, py_digit));
+		Py_DECREF(py_digit);
+		if (numerator == NULL) goto error;
+	}
+
+	/* Add in the sign bit. */
+	if (is_negative) {
+		INPLACE_UPDATE(numerator,
+			       long_methods->nb_negative(numerator));
+		if (numerator == NULL) goto error;
+	}
+
+	/* now self = numerator * 2**exponent exactly; fold in 2**exponent */
+	denominator = PyLong_FromLong(1);
+	py_exponent = PyLong_FromLong(labs(exponent));
+	if (py_exponent == NULL) goto error;
+	INPLACE_UPDATE(py_exponent,
+		       long_methods->nb_lshift(denominator, py_exponent));
+	if (py_exponent == NULL) goto error;
+	if (exponent > 0) {
+		INPLACE_UPDATE(numerator,
+			       long_methods->nb_multiply(numerator,
+							 py_exponent));
+		if (numerator == NULL) goto error;
+	}
+	else {
+		Py_DECREF(denominator);
+		denominator = py_exponent;
+		py_exponent = NULL;
+	}
+
+	result_pair = PyTuple_Pack(2, numerator, denominator);
+
+#undef INPLACE_UPDATE
+error:
+	Py_XDECREF(py_exponent);
+	Py_XDECREF(py_chunk);
+	Py_XDECREF(denominator);
+	Py_XDECREF(numerator);
+	return result_pair;
+}
+
+PyDoc_STRVAR(float_as_integer_ratio_doc,
+"float.as_integer_ratio() -> (int, int)\n"
+"\n"
+"Returns a pair of integers, not necessarily in lowest terms, whose\n"
+"ratio is exactly equal to the original float. This method raises an\n"
+"OverflowError on infinities and a ValueError on nans. The resulting\n"
+"denominator will be positive.\n"
+"\n"
+">>> (10.0).as_integer_ratio()\n"
+"(167772160L, 16777216L)\n"
+">>> (0.0).as_integer_ratio()\n"
+"(0, 1)\n"
+">>> (-.25).as_integer_ratio()\n"
+"(-134217728L, 536870912L)");
+
 
 static PyObject *
 float_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
@@ -1281,6 +1438,8 @@ static PyMethodDef float_methods[] = {
 	{"__round__",	(PyCFunction)float_round, METH_VARARGS,
          "Returns the Integral closest to x, rounding half toward even.\n"
          "When an argument is passed, works like built-in round(x, ndigits)."},
+	{"as_integer_ratio", (PyCFunction)float_as_integer_ratio, METH_NOARGS,
+	 float_as_integer_ratio_doc},
 	{"__getnewargs__",	(PyCFunction)float_getnewargs,	METH_NOARGS},
 	{"__getformat__",	(PyCFunction)float_getformat,	
 	 METH_O|METH_CLASS,		float_getformat_doc},
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 33b2023f0ca..1d6336ce158 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -33,6 +33,24 @@ struct method_cache_entry {
 
 static struct method_cache_entry method_cache[1 << MCACHE_SIZE_EXP];
 static unsigned int next_version_tag = 0;
+static void type_modified(PyTypeObject *);
+
+unsigned int
+PyType_ClearCache(void)
+{
+	Py_ssize_t i;
+	unsigned int cur_version_tag = next_version_tag - 1;
+	
+	for (i = 0; i < (1 << MCACHE_SIZE_EXP); i++) {
+		method_cache[i].version = 0;
+		Py_CLEAR(method_cache[i].name);
+		method_cache[i].value = NULL;
+	}
+	next_version_tag = 0;
+	/* mark all version tags as invalid */
+	type_modified(&PyBaseObject_Type);
+	return cur_version_tag;
+}
 
 static void
 type_modified(PyTypeObject *type)
diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 9b72908df6a..7cee8e4eda6 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -404,6 +404,9 @@ Py_Finalize(void)
 	Py_XDECREF(warnings_module);
 	warnings_module = NULL;
 
+	/* Clear type lookup cache */
+	PyType_ClearCache();
+
 	/* Collect garbage.  This may call finalizers; it's nice to call these
 	 * before all modules are destroyed.
 	 * XXX If a __del__ or weakref callback is triggered here, and tries to
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 499f3288be2..e536f0aad35 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -730,6 +730,17 @@ a 11-tuple where the entries in the tuple are counts of:\n\
 10. Number of stack pops performed by call_function()"
 );
 
+static PyObject *
+sys_cleartypecache(PyObject* self, PyObject* args)
+{
+	PyType_ClearCache();
+	Py_RETURN_NONE;
+}
+
+PyDoc_STRVAR(cleartypecache_doc,
+"_cleartypecache() -> None\n\
+Clear the internal type lookup cache.");
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -752,6 +763,8 @@ static PyMethodDef sys_methods[] = {
 	/* Might as well keep this in alphabetic order */
 	{"callstats", (PyCFunction)PyEval_GetCallStats, METH_NOARGS,
 	 callstats_doc},
+	{"_cleartypecache", sys_cleartypecache, METH_NOARGS,
+	 cleartypecache_doc},
 	{"_current_frames", sys_current_frames, METH_NOARGS,
 	 current_frames_doc},
 	{"displayhook",	sys_displayhook, METH_O, displayhook_doc},