#2538: bytes objects can only provide read-only buffers

Lib/test/test_bytes.py

@@ -453,6 +453,11 @@ class BaseBytesTest(unittest.TestCase):
 class BytesTest(BaseBytesTest):
     type2test = bytes
 
+    def test_buffer_is_readonly(self):
+        with open(sys.stdin.fileno(), "rb", buffering=0) as f:
+            self.assertRaises(TypeError, f.readinto, b"")
+
+
 class ByteArrayTest(BaseBytesTest):
     type2test = bytearray