Issue #19369: Optimized the usage of __length_hint__().

Misc/NEWS

@@ -10,6 +10,8 @@ Projected release date: 2013-11-24
 Core and Builtins
 -----------------
 
+- Issue #19369: Optimized the usage of __length_hint__().
+
 - Issue #18603: Ensure that PyOS_mystricmp and PyOS_mystrnicmp are in the
   Python executable and not removed by the linker's optimizer.
 

Objects/abstract.c

@@ -82,6 +82,7 @@ PyObject_LengthHint(PyObject *o, Py_ssize_t defaultvalue)
     PyObject *hint, *result;
     Py_ssize_t res;
     _Py_IDENTIFIER(__length_hint__);
+    if (_PyObject_HasLen(o)) {
         res = PyObject_Length(o);
         if (res < 0 && PyErr_Occurred()) {
             if (!PyErr_ExceptionMatches(PyExc_TypeError)) {
@@ -92,6 +93,7 @@ PyObject_LengthHint(PyObject *o, Py_ssize_t defaultvalue)
         else {
             return res;
         }
+    }
     hint = _PyObject_LookupSpecial(o, &PyId___length_hint__);
     if (hint == NULL) {
         if (PyErr_Occurred()) {