5 files changed, 58 insertions, 35 deletions

diff --git a/Objects/abstract.c b/Objects/abstract.c
index a2737dd..b6fc478 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -64,49 +64,67 @@ PyObject_Length(PyObject *o)
 }
 #define PyObject_Length PyObject_Size
 
+int
+_PyObject_HasLen(PyObject *o) {
+    return (Py_TYPE(o)->tp_as_sequence && Py_TYPE(o)->tp_as_sequence->sq_length) ||
+        (Py_TYPE(o)->tp_as_mapping && Py_TYPE(o)->tp_as_mapping->mp_length);
+}
 
 /* The length hint function returns a non-negative value from o.__len__()
-   or o.__length_hint__().  If those methods aren't found or return a negative
-   value, then the defaultvalue is returned.  If one of the calls fails,
-   this function returns -1.
+   or o.__length_hint__().  If those methods aren't found.  If one of the calls
+   fails this function returns -1.
 */
 
 Py_ssize_t
-_PyObject_LengthHint(PyObject *o, Py_ssize_t defaultvalue)
+PyObject_LengthHint(PyObject *o, Py_ssize_t defaultvalue)
 {
     _Py_IDENTIFIER(__length_hint__);
-    PyObject *ro, *hintmeth;
-    Py_ssize_t rv;
-
-    /* try o.__len__() */
-    rv = PyObject_Size(o);
-    if (rv >= 0)
-        return rv;
-    if (PyErr_Occurred()) {
-        if (!PyErr_ExceptionMatches(PyExc_TypeError))
+    Py_ssize_t res = PyObject_Length(o);
+    if (res < 0 && PyErr_Occurred()) {
+        if (!PyErr_ExceptionMatches(PyExc_TypeError)) {
             return -1;
+        }
         PyErr_Clear();
     }
-
-    /* try o.__length_hint__() */
-    hintmeth = _PyObject_LookupSpecial(o, &PyId___length_hint__);
-    if (hintmeth == NULL) {
-        if (PyErr_Occurred())
+    else {
+        return res;
+    }
+    PyObject *hint = _PyObject_LookupSpecial(o, &PyId___length_hint__);
+    if (hint == NULL) {
+        if (PyErr_Occurred()) {
             return -1;
-        else
+        }
+        return defaultvalue;
+    }
+    PyObject *result = PyObject_CallFunctionObjArgs(hint, NULL);
+    Py_DECREF(hint);
+    if (result == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+            PyErr_Clear();
             return defaultvalue;
+        }
+        return -1;
     }
-    ro = PyObject_CallFunctionObjArgs(hintmeth, NULL);
-    Py_DECREF(hintmeth);
-    if (ro == NULL) {
-        if (!PyErr_ExceptionMatches(PyExc_TypeError))
-            return -1;
-        PyErr_Clear();
+    else if (result == Py_NotImplemented) {
+        Py_DECREF(result);
         return defaultvalue;
     }
-    rv = PyLong_Check(ro) ? PyLong_AsSsize_t(ro) : defaultvalue;
-    Py_DECREF(ro);
-    return rv;
+    if (!PyLong_Check(result)) {
+        PyErr_Format(PyExc_TypeError, "Length hint must be an integer, not %s",
+            Py_TYPE(result)->tp_name);
+        Py_DECREF(result);
+        return -1;
+    }
+    defaultvalue = PyLong_AsSsize_t(result);
+    Py_DECREF(result);
+    if (defaultvalue < 0 && PyErr_Occurred()) {
+        return -1;
+    }
+    if (defaultvalue < 0) {
+        PyErr_Format(PyExc_ValueError, "__length_hint__() should return >= 0");
+        return -1;
+    }
+    return defaultvalue;
 }
 
 PyObject *
@@ -1687,7 +1705,7 @@ PySequence_Tuple(PyObject *v)
         return NULL;
 
     /* Guess result size and allocate space. */
-    n = _PyObject_LengthHint(v, 10);
+    n = PyObject_LengthHint(v, 10);
     if (n == -1)
         goto Fail;
     result = PyTuple_New(n);
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index 2bb3a29..26c76d2 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -2282,7 +2282,7 @@ bytearray_extend(PyByteArrayObject *self, PyObject *arg)
         return NULL;
 
     /* Try to determine the length of the argument. 32 is arbitrary. */
-    buf_size = _PyObject_LengthHint(arg, 32);
+    buf_size = PyObject_LengthHint(arg, 32);
     if (buf_size == -1) {
         Py_DECREF(it);
         return NULL;
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index bf9259f..25c2326 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -2651,7 +2651,7 @@ PyBytes_FromObject(PyObject *x)
     }
 
     /* For iterator version, create a string object and resize as needed */
-    size = _PyObject_LengthHint(x, 64);
+    size = PyObject_LengthHint(x, 64);
     if (size == -1 && PyErr_Occurred())
         return NULL;
     /* Allocate an extra byte to prevent PyBytes_FromStringAndSize() from
diff --git a/Objects/iterobject.c b/Objects/iterobject.c
index 3cfbeaf..cf4af5b 100644
--- a/Objects/iterobject.c
+++ b/Objects/iterobject.c
@@ -76,9 +76,14 @@ iter_len(seqiterobject *it)
     Py_ssize_t seqsize, len;
 
     if (it->it_seq) {
-        seqsize = PySequence_Size(it->it_seq);
-        if (seqsize == -1)
-            return NULL;
+        if (_PyObject_HasLen(it->it_seq)) {
+            seqsize = PySequence_Size(it->it_seq);
+            if (seqsize == -1)
+                return NULL;
+        }
+        else {
+            return Py_NotImplemented;
+        }
         len = seqsize - it->it_index;
         if (len >= 0)
             return PyLong_FromSsize_t(len);
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 6e0d094..4cc34b5 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -826,7 +826,7 @@ listextend(PyListObject *self, PyObject *b)
     iternext = *it->ob_type->tp_iternext;
 
     /* Guess a result list size. */
-    n = _PyObject_LengthHint(b, 8);
+    n = PyObject_LengthHint(b, 8);
     if (n == -1) {
         Py_DECREF(it);
         return NULL;