For collections.deque() objects, expose the maxlen parameter as a read-only attribute.
diff --git a/Misc/NEWS b/Misc/NEWS
index ad28735..b870bcf 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -195,6 +195,8 @@
 Library
 -------
 
+- collections.deque() objects now have a read-only attribute called maxlen.
+
 - Issue #2638: Show a window constructed with tkSimpleDialog.Dialog only after
   it is has been populated and properly configured in order to prevent
   window flashing.