Add a versionadded to Counter.subtract() doc.

diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index f4ba51ab9ad7942f4f623b1fbf9288e0b3de1ef6..f57910124aae38a4609955734edf35c27715a8e7 100644 (file)
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -241,6 +241,8 @@ For example::
             >>> c.subtract(d)
             Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})
 
+      .. versionadded:: 2.7
+
    The usual dictionary methods are available for :class:`Counter` objects
    except for two which work differently for counters.