Give itertools.repeat() a length method.

Lib/test/test_itertools.py

@@ -607,6 +607,12 @@ class TestVariousIteratorArgs(unittest.TestCase):
             self.assertRaises(TypeError, list, tee(N(s))[0])
             self.assertRaises(ZeroDivisionError, list, tee(E(s))[0])
 
+class LengthTransparency(unittest.TestCase):
+
+    def test_repeat(self):
+        self.assertEqual(len(repeat(None, 50)), 50)
+        self.assertRaises(TypeError, len, repeat(None))
+
 class RegressionTests(unittest.TestCase):
 
     def test_sf_793826(self):
@@ -826,7 +832,7 @@ __test__ = {'libreftest' : libreftest}
 
 def test_main(verbose=None):
     test_classes = (TestBasicOps, TestVariousIteratorArgs, TestGC,
-                    RegressionTests)
+                    RegressionTests, LengthTransparency)
     test_support.run_unittest(*test_classes)
 
     # verify reference counting

Modules/itertoolsmodule.c

@@ -2347,6 +2347,19 @@ repeat_next(repeatobject *ro)
 	return ro->element;
 }
 
+static int
+repeat_len(repeatobject *ro)
+{
+        if (ro->cnt == -1)
+                PyErr_SetString(PyExc_TypeError, "len() of unsized object");
+        return (int)(ro->cnt);
+}
+
+static PySequenceMethods repeat_as_sequence = {
+	(inquiry)repeat_len,		/* sq_length */
+	0,				/* sq_concat */
+};
+
 PyDoc_STRVAR(repeat_doc,
 "repeat(element [,times]) -> create an iterator which returns the element\n\
 for the specified number of times.  If not specified, returns the element\n\
@@ -2366,7 +2379,7 @@ static PyTypeObject repeat_type = {
 	0,				/* tp_compare */
 	0,				/* tp_repr */
 	0,				/* tp_as_number */
-	0,				/* tp_as_sequence */
+	&repeat_as_sequence,		/* tp_as_sequence */
 	0,				/* tp_as_mapping */
 	0,				/* tp_hash */
 	0,				/* tp_call */