Issue #27443: __length_hint__() of bytearray itearator no longer return

negative integer for resized bytearray.

3 files changed, 18 insertions, 1 deletions

diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index 9d878caa44..05dc26afaf 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -1328,6 +1328,16 @@ class ByteArrayTest(BaseBytesTest, unittest.TestCase):
 
     test_exhausted_iterator = test.list_tests.CommonTest.test_exhausted_iterator
 
+    def test_iterator_length_hint(self):
+        # Issue 27443: __length_hint__ can return negative integer
+        ba = bytearray(b'ab')
+        it = iter(ba)
+        next(it)
+        ba.clear()
+        # Shouldn't raise an error
+        self.assertEqual(list(it), [])
+
+
 class AssortedBytesTest(unittest.TestCase):
     #
     # Test various combinations of bytes and bytearray
diff --git a/Misc/NEWS b/Misc/NEWS
index 7dc5887dde..014ac547c1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@ What's New in Python 3.6.0 alpha 3
 Core and Builtins
 -----------------
 
+- Issue #27443: __length_hint__() of bytearray itearator no longer return
+  negative integer for resized bytearray.
+
 - Issue #27007: The fromhex() class methods of bytes and bytearray subclasses
   now return an instance of corresponding subclass.
 
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index 85990e0be4..50da637491 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -2303,8 +2303,12 @@ static PyObject *
 bytearrayiter_length_hint(bytesiterobject *it)
 {
     Py_ssize_t len = 0;
-    if (it->it_seq)
+    if (it->it_seq) {
         len = PyByteArray_GET_SIZE(it->it_seq) - it->it_index;
+        if (len < 0) {
+            len = 0;
+        }
+    }
     return PyLong_FromSsize_t(len);
 }