Convert iterator __len__() methods to a private API.

16 files changed, 169 insertions, 94 deletions

diff --git a/Include/abstract.h b/Include/abstract.h
index 17ce105..7e0bc4d 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -422,6 +422,21 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
      PyAPI_FUNC(int) PyObject_Length(PyObject *o);
 #define PyObject_Length PyObject_Size
 
+     PyAPI_FUNC(int) _PyObject_LengthCue(PyObject *o);
+
+       /*
+         Return the size of object o.  If the object, o, provides
+	 both sequence and mapping protocols, the sequence size is
+	 returned. On error, -1 is returned.  If the object provides
+	 a _length_cue() method, its value is returned.  This is the 
+	 equivalent to the Python expression: 
+		try:
+			return len(o)
+		except (AttributeError, TypeError):
+			if hasattr(o, '_length_cue'):
+				return o._length_cue()
+			raise
+       */
 
      PyAPI_FUNC(PyObject *) PyObject_GetItem(PyObject *o, PyObject *key);
 
diff --git a/Lib/test/test_enumerate.py b/Lib/test/test_enumerate.py
index b6a18ee..e0a272e 100644
--- a/Lib/test/test_enumerate.py
+++ b/Lib/test/test_enumerate.py
@@ -144,6 +144,7 @@ class TestReversed(unittest.TestCase):
 
     def test_len(self):
         # This is an implementation detail, not an interface requirement
+        from test.test_iterlen import len
         for s in ('hello', tuple('hello'), list('hello'), xrange(5)):
             self.assertEqual(len(reversed(s)), len(s))
             r = reversed(s)
diff --git a/Lib/test/test_iterlen.py b/Lib/test/test_iterlen.py
index b51263d..1770de2 100644
--- a/Lib/test/test_iterlen.py
+++ b/Lib/test/test_iterlen.py
@@ -43,12 +43,22 @@ enumerate(iter('abc')).
 
 import unittest
 from test import test_support
-from itertools import repeat, count
+from itertools import repeat
 from collections import deque
 from UserList import UserList
+from __builtin__ import len as _len
 
 n = 10
 
+def len(obj):
+    try:
+        return _len(obj)
+    except TypeError:
+        try:
+            return obj._length_cue()
+        except AttributeError:
+            raise TypeError
+
 class TestInvariantWithoutMutations(unittest.TestCase):
 
     def test_invariant(self):
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 5db128c..635d156 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -670,6 +670,7 @@ class TestVariousIteratorArgs(unittest.TestCase):
 class LengthTransparency(unittest.TestCase):
 
     def test_repeat(self):
+        from test.test_iterlen import len
         self.assertEqual(len(repeat(None, 50)), 50)
         self.assertRaises(TypeError, len, repeat(None))
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 00bd247..409126a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,10 @@ What's New in Python 2.5 alpha 1?
 Core and builtins
 -----------------
 
+- All iterators now have a Boolean value of true.  Formerly, some iterators
+  supported a __len__() method which evaluated to False when the iterator
+  was empty.
+
 - On 64-bit platforms, when __len__() returns a value that cannot be
   represented as a C int, raise OverflowError.
 
diff --git a/Modules/collectionsmodule.c b/Modules/collectionsmodule.c
index ffe1a96..1a8258e 100644
--- a/Modules/collectionsmodule.c
+++ b/Modules/collectionsmodule.c
@@ -935,15 +935,17 @@ dequeiter_next(dequeiterobject *it)
 	return item;
 }
 
-static int
+static PyObject *
 dequeiter_len(dequeiterobject *it)
 {
-	return it->counter;
+	return PyInt_FromLong(it->counter);
 }
 
-static PySequenceMethods dequeiter_as_sequence = {
-	(inquiry)dequeiter_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef dequeiter_methods[] = {
+	{"_length_cue", (PyCFunction)dequeiter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 PyTypeObject dequeiter_type = {
@@ -960,7 +962,7 @@ PyTypeObject dequeiter_type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&dequeiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -976,6 +978,7 @@ PyTypeObject dequeiter_type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)dequeiter_next,		/* tp_iternext */
+	dequeiter_methods,			/* tp_methods */
 	0,
 };
 
@@ -1042,7 +1045,7 @@ PyTypeObject dequereviter_type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&dequeiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -1058,6 +1061,7 @@ PyTypeObject dequereviter_type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)dequereviter_next,	/* tp_iternext */
+	dequeiter_methods,			/* tp_methods */
 	0,
 };
 
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 34b37be..5ec5b8d 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -2336,17 +2336,21 @@ repeat_repr(repeatobject *ro)
 	return result;
 }	
 
-static int
+static PyObject *
 repeat_len(repeatobject *ro)
 {
-        if (ro->cnt == -1)
+        if (ro->cnt == -1) {
                 PyErr_SetString(PyExc_TypeError, "len() of unsized object");
-        return (int)(ro->cnt);
+		return NULL;
+	}
+        return PyInt_FromLong(ro->cnt);
 }
 
-static PySequenceMethods repeat_as_sequence = {
-	(inquiry)repeat_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef repeat_methods[] = {
+	{"_length_cue", (PyCFunction)repeat_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 PyDoc_STRVAR(repeat_doc,
@@ -2368,7 +2372,7 @@ static PyTypeObject repeat_type = {
 	0,				/* tp_compare */
 	(reprfunc)repeat_repr,		/* tp_repr */
 	0,				/* tp_as_number */
-	&repeat_as_sequence,		/* tp_as_sequence */
+	0,				/* tp_as_sequence */
 	0,				/* tp_as_mapping */
 	0,				/* tp_hash */
 	0,				/* tp_call */
@@ -2385,7 +2389,7 @@ static PyTypeObject repeat_type = {
 	0,				/* tp_weaklistoffset */
 	PyObject_SelfIter,		/* tp_iter */
 	(iternextfunc)repeat_next,	/* tp_iternext */
-	0,				/* tp_methods */
+	repeat_methods,			/* tp_methods */
 	0,				/* tp_members */
 	0,				/* tp_getset */
 	0,				/* tp_base */
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 94af3da..1f8feb5 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -81,6 +81,31 @@ PyObject_Length(PyObject *o)
 }
 #define PyObject_Length PyObject_Size
 
+int
+_PyObject_LengthCue(PyObject *o)
+{
+	int rv = PyObject_Size(o);
+	if (rv != -1)
+		return rv;
+	if (PyErr_ExceptionMatches(PyExc_TypeError) ||
+	    PyErr_ExceptionMatches(PyExc_AttributeError)) {
+		PyObject *err_type, *err_value, *err_tb, *ro;
+
+		PyErr_Fetch(&err_type, &err_value, &err_tb);
+		ro = PyObject_CallMethod(o, "_length_cue", NULL);
+		if (ro != NULL) {
+			rv = (int)PyInt_AsLong(ro);
+			Py_DECREF(ro);
+			Py_XDECREF(err_type);
+			Py_XDECREF(err_value);
+			Py_XDECREF(err_tb);
+			return rv;
+		}
+		PyErr_Restore(err_type, err_value, err_tb);
+	}
+	return -1;
+}
+
 PyObject *
 PyObject_GetItem(PyObject *o, PyObject *key)
 {
@@ -1399,7 +1424,7 @@ PySequence_Tuple(PyObject *v)
 		return NULL;
 
 	/* Guess result size and allocate space. */
-	n = PyObject_Size(v);
+	n = _PyObject_LengthCue(v);
 	if (n < 0) {
 		if (!PyErr_ExceptionMatches(PyExc_TypeError)  &&
 		    !PyErr_ExceptionMatches(PyExc_AttributeError)) {
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index e90aca4..42e55e8 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -2054,17 +2054,20 @@ dictiter_dealloc(dictiterobject *di)
 	PyObject_Del(di);
 }
 
-static int
+static PyObject *
 dictiter_len(dictiterobject *di)
 {
+	int len = 0;
 	if (di->di_dict != NULL && di->di_used == di->di_dict->ma_used)
-		return di->len;
-	return 0;
+		len = di->len;
+	return PyInt_FromLong(len);
 }
 
-static PySequenceMethods dictiter_as_sequence = {
-	(inquiry)dictiter_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef dictiter_methods[] = {
+	{"_length_cue", (PyCFunction)dictiter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 static PyObject *dictiter_iternextkey(dictiterobject *di)
@@ -2120,7 +2123,7 @@ PyTypeObject PyDictIterKey_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&dictiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -2136,6 +2139,8 @@ PyTypeObject PyDictIterKey_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)dictiter_iternextkey,	/* tp_iternext */
+	dictiter_methods,			/* tp_methods */
+	0,
 };
 
 static PyObject *dictiter_iternextvalue(dictiterobject *di)
@@ -2191,7 +2196,7 @@ PyTypeObject PyDictIterValue_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&dictiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -2207,6 +2212,8 @@ PyTypeObject PyDictIterValue_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)dictiter_iternextvalue,	/* tp_iternext */
+	dictiter_methods,			/* tp_methods */
+	0,
 };
 
 static PyObject *dictiter_iternextitem(dictiterobject *di)
@@ -2276,7 +2283,7 @@ PyTypeObject PyDictIterItem_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&dictiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -2292,4 +2299,6 @@ PyTypeObject PyDictIterItem_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)dictiter_iternextitem,	/* tp_iternext */
+	dictiter_methods,			/* tp_methods */
+	0,
 };
diff --git a/Objects/enumobject.c b/Objects/enumobject.c
index aac88db..f74acdc 100644
--- a/Objects/enumobject.c
+++ b/Objects/enumobject.c
@@ -239,23 +239,25 @@ PyDoc_STRVAR(reversed_doc,
 "\n"
 "Return a reverse iterator");
 
-static int
+static PyObject *
 reversed_len(reversedobject *ro)
 {
 	int position, seqsize;
 
 	if (ro->seq == NULL)
-		return 0;
+		return PyInt_FromLong(0);
 	seqsize = PySequence_Size(ro->seq);
 	if (seqsize == -1)
-		return -1;
+		return NULL;
 	position = ro->index + 1;
-	return (seqsize < position)  ?  0  :  position;
+	return PyInt_FromLong((seqsize < position)  ?  0  :  position);
 }
 
-static PySequenceMethods reversed_as_sequence = {
-	(inquiry)reversed_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef reversediter_methods[] = {
+	{"_length_cue", (PyCFunction)reversed_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 PyTypeObject PyReversed_Type = {
@@ -272,7 +274,7 @@ PyTypeObject PyReversed_Type = {
 	0,                              /* tp_compare */
 	0,                              /* tp_repr */
 	0,                              /* tp_as_number */
-	&reversed_as_sequence,          /* tp_as_sequence */
+	0,				/* tp_as_sequence */
 	0,                              /* tp_as_mapping */
 	0,                              /* tp_hash */
 	0,                              /* tp_call */
@@ -289,7 +291,7 @@ PyTypeObject PyReversed_Type = {
 	0,                              /* tp_weaklistoffset */
 	PyObject_SelfIter,		/* tp_iter */
 	(iternextfunc)reversed_next,    /* tp_iternext */
-	0,				/* tp_methods */
+	reversediter_methods,		/* tp_methods */
 	0,                              /* tp_members */
 	0,                              /* tp_getset */
 	0,                              /* tp_base */
diff --git a/Objects/iterobject.c b/Objects/iterobject.c
index b414cc2..fdee3ca 100644
--- a/Objects/iterobject.c
+++ b/Objects/iterobject.c
@@ -71,7 +71,7 @@ iter_iternext(PyObject *iterator)
 	return NULL;
 }
 
-static int
+static PyObject *
 iter_len(seqiterobject *it)
 {
 	int seqsize, len;
@@ -79,17 +79,19 @@ iter_len(seqiterobject *it)
 	if (it->it_seq) {
 		seqsize = PySequence_Size(it->it_seq);
 		if (seqsize == -1)
-			return -1;
+			return NULL;
 		len = seqsize - it->it_index;
 		if (len >= 0)
-			return len;
+			return PyInt_FromLong(len);
 	}
-	return 0;
+	return PyInt_FromLong(0);
 }
 
-static PySequenceMethods iter_as_sequence = {
-	(inquiry)iter_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef seqiter_methods[] = {
+	{"_length_cue", (PyCFunction)iter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 PyTypeObject PySeqIter_Type = {
@@ -106,7 +108,7 @@ PyTypeObject PySeqIter_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&iter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -122,13 +124,8 @@ PyTypeObject PySeqIter_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)iter_iternext,		/* tp_iternext */
-	0,					/* tp_methods */
+	seqiter_methods,			/* tp_methods */
 	0,					/* tp_members */
-	0,					/* tp_getset */
-	0,					/* tp_base */
-	0,					/* tp_dict */
-	0,					/* tp_descr_get */
-	0,					/* tp_descr_set */
 };
 
 /* -------------------------------------- */
@@ -236,10 +233,4 @@ PyTypeObject PyCallIter_Type = {
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)calliter_iternext,	/* tp_iternext */
 	0,					/* tp_methods */
-	0,					/* tp_members */
-	0,					/* tp_getset */
-	0,					/* tp_base */
-	0,					/* tp_dict */
-	0,					/* tp_descr_get */
-	0,					/* tp_descr_set */
 };
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 3b7358a..1a96361 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -775,7 +775,7 @@ listextend(PyListObject *self, PyObject *b)
 	iternext = *it->ob_type->tp_iternext;
 
 	/* Guess a result list size. */
-	n = PyObject_Size(b);
+	n = _PyObject_LengthCue(b);
 	if (n < 0) {
 		if (!PyErr_ExceptionMatches(PyExc_TypeError)  &&
 		    !PyErr_ExceptionMatches(PyExc_AttributeError)) {
@@ -2764,21 +2764,23 @@ listiter_next(listiterobject *it)
 	return NULL;
 }
 
-static int
+static PyObject *
 listiter_len(listiterobject *it)
 {
 	int len;
 	if (it->it_seq) {
 		len = PyList_GET_SIZE(it->it_seq) - it->it_index;
 		if (len >= 0)
-			return len;
+			return PyInt_FromLong((long)len);
 	}
-	return 0;
+	return PyInt_FromLong(0);
 }
 
-static PySequenceMethods listiter_as_sequence = {
-	(inquiry)listiter_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef listiter_methods[] = {
+	{"_length_cue", (PyCFunction)listiter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 PyTypeObject PyListIter_Type = {
@@ -2795,7 +2797,7 @@ PyTypeObject PyListIter_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&listiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -2811,13 +2813,8 @@ PyTypeObject PyListIter_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)listiter_next,		/* tp_iternext */
-	0,					/* tp_methods */
+	listiter_methods,			/* tp_methods */
 	0,					/* tp_members */
-	0,					/* tp_getset */
-	0,					/* tp_base */
-	0,					/* tp_dict */
-	0,					/* tp_descr_get */
-	0,					/* tp_descr_set */
 };
 
 /*********************** List Reverse Iterator **************************/
diff --git a/Objects/rangeobject.c b/Objects/rangeobject.c
index 8b5650a..3cc5504 100644
--- a/Objects/rangeobject.c
+++ b/Objects/rangeobject.c
@@ -262,17 +262,18 @@ rangeiter_next(rangeiterobject *r)
 	return NULL;
 }
 
-static int
+static PyObject *
 rangeiter_len(rangeiterobject *r)
 {
-	return r->len - r->index;
+	return PyInt_FromLong(r->len - r->index);
 }
 
-static PySequenceMethods rangeiter_as_sequence = {
-	(inquiry)rangeiter_len,		/* sq_length */
-	0,				/* sq_concat */
-};
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
 
+static PyMethodDef rangeiter_methods[] = {
+	{"_length_cue", (PyCFunction)rangeiter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
+};
 
 static PyTypeObject Pyrangeiter_Type = {
 	PyObject_HEAD_INIT(&PyType_Type)
@@ -288,7 +289,7 @@ static PyTypeObject Pyrangeiter_Type = {
 	0,                                      /* tp_compare */
 	0,                                      /* tp_repr */
 	0,                                      /* tp_as_number */
-	&rangeiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,                                      /* tp_as_mapping */
 	0,                                      /* tp_hash */
 	0,                                      /* tp_call */
@@ -304,5 +305,6 @@ static PyTypeObject Pyrangeiter_Type = {
 	0,                                      /* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)rangeiter_next,		/* tp_iternext */
-	0,					/* tp_methods */
+	rangeiter_methods,			/* tp_methods */
+	0,
 };
diff --git a/Objects/setobject.c b/Objects/setobject.c
index c4cd562..29a9184 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -749,17 +749,20 @@ setiter_dealloc(setiterobject *si)
 	PyObject_Del(si);
 }
 
-static int
+static PyObject *
 setiter_len(setiterobject *si)
 {
+	int len = 0;
 	if (si->si_set != NULL && si->si_used == si->si_set->used)
-		return si->len;
-	return 0;
+		len = si->len;
+	return PyInt_FromLong(len);
 }
 
-static PySequenceMethods setiter_as_sequence = {
-	(inquiry)setiter_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef setiter_methods[] = {
+	{"_length_cue", (PyCFunction)setiter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 static PyObject *setiter_iternext(setiterobject *si)
@@ -814,7 +817,7 @@ static PyTypeObject PySetIter_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&setiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -830,6 +833,8 @@ static PyTypeObject PySetIter_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)setiter_iternext,		/* tp_iternext */
+	setiter_methods,			/* tp_methods */
+	0,
 };
 
 static int
diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index ea7d753..76e5de3 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -851,17 +851,20 @@ tupleiter_next(tupleiterobject *it)
 	return NULL;
 }
 
-static int
+static PyObject *
 tupleiter_len(tupleiterobject *it)
 {
+	int len = 0;
 	if (it->it_seq)
-		return PyTuple_GET_SIZE(it->it_seq) - it->it_index;
-	return 0;
+		len = PyTuple_GET_SIZE(it->it_seq) - it->it_index;
+	return PyInt_FromLong(len);
 }
 
-static PySequenceMethods tupleiter_as_sequence = {
-	(inquiry)tupleiter_len,		/* sq_length */
-	0,				/* sq_concat */
+PyDoc_STRVAR(length_cue_doc, "Private method returning an estimate of len(list(it)).");
+
+static PyMethodDef tupleiter_methods[] = {
+	{"_length_cue", (PyCFunction)tupleiter_len, METH_NOARGS, length_cue_doc},
+ 	{NULL,		NULL}		/* sentinel */
 };
 
 PyTypeObject PyTupleIter_Type = {
@@ -878,7 +881,7 @@ PyTypeObject PyTupleIter_Type = {
 	0,					/* tp_compare */
 	0,					/* tp_repr */
 	0,					/* tp_as_number */
-	&tupleiter_as_sequence,			/* tp_as_sequence */
+	0,					/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
 	0,					/* tp_call */
@@ -894,4 +897,6 @@ PyTypeObject PyTupleIter_Type = {
 	0,					/* tp_weaklistoffset */
 	PyObject_SelfIter,			/* tp_iter */
 	(iternextfunc)tupleiter_next,		/* tp_iternext */
+	tupleiter_methods,			/* tp_methods */
+	0,
 };
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index dca8555..3e5f4eb 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -221,7 +221,7 @@ builtin_filter(PyObject *self, PyObject *args)
 		goto Fail_arg;
 
 	/* Guess a result list size. */
-	len = PyObject_Size(seq);
+	len = _PyObject_LengthCue(seq);
 	if (len < 0) {
 		if (!PyErr_ExceptionMatches(PyExc_TypeError)  &&
 		    !PyErr_ExceptionMatches(PyExc_AttributeError)) {
@@ -873,7 +873,7 @@ builtin_map(PyObject *self, PyObject *args)
 		}
 
 		/* Update len. */
-		curlen = PyObject_Size(curseq);
+		curlen = _PyObject_LengthCue(curseq);
 		if (curlen < 0) {
 			if (!PyErr_ExceptionMatches(PyExc_TypeError)  &&
 			    !PyErr_ExceptionMatches(PyExc_AttributeError)) {
@@ -2108,7 +2108,7 @@ builtin_zip(PyObject *self, PyObject *args)
 	len = -1;	/* unknown */
 	for (i = 0; i < itemsize; ++i) {
 		PyObject *item = PyTuple_GET_ITEM(args, i);
-		int thislen = PyObject_Size(item);
+		int thislen = _PyObject_LengthCue(item);
 		if (thislen < 0) {
 			if (!PyErr_ExceptionMatches(PyExc_TypeError)  &&
 			    !PyErr_ExceptionMatches(PyExc_AttributeError)) {