bpo-14112: Allow beginners to explore shallowness in greater depth ;-) (GH-15465) (GH-15469)

(cherry picked from commit 69ee87e99c)

Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>

Doc/library/copy.rst

@@ -31,6 +31,7 @@ Interface summary:
 
    Raised for module specific errors.
 
+.. _shallow_vs_deep_copy:
 
 The difference between shallow and deep copying is only relevant for compound
 objects (objects that contain other objects, like lists or class instances):

Doc/tutorial/introduction.rst

@@ -394,7 +394,8 @@ indexed and sliced::
    [9, 16, 25]
 
 All slice operations return a new list containing the requested elements.  This
-means that the following slice returns a new (shallow) copy of the list::
+means that the following slice returns a
+:ref:`shallow copy <shallow_vs_deep_copy>` of the list::
 
    >>> squares[:]
    [1, 4, 9, 16, 25]