[3.13] gh-122511: Improve documentation for object identity of mutable/immutable types (GH-122512) (#122778)

gh-122511: Improve documentation for object identity of mutable/immutable types (GH-122512)
(cherry picked from commit 76bdeeb)

Co-authored-by: Bénédikt Tran <[email protected]>
Co-authored-by: Adam Turner <[email protected]>

Author: 3 people

Doc/reference/datamodel.rst

@@ -106,12 +106,16 @@ that mutable object is changed.
 Types affect almost all aspects of object behavior.  Even the importance of
 object identity is affected in some sense: for immutable types, operations that
 compute new values may actually return a reference to any existing object with
-the same type and value, while for mutable objects this is not allowed.  E.g.,
-after ``a = 1; b = 1``, ``a`` and ``b`` may or may not refer to the same object
-with the value one, depending on the implementation, but after ``c = []; d =
-[]``, ``c`` and ``d`` are guaranteed to refer to two different, unique, newly
-created empty lists. (Note that ``c = d = []`` assigns the same object to both
-``c`` and ``d``.)
+the same type and value, while for mutable objects this is not allowed.
+For example, after ``a = 1; b = 1``, *a* and *b* may or may not refer to
+the same object with the value one, depending on the implementation.
+This is because :class:`int` is an immutable type, so the reference to ``1``
+can be reused. This behaviour depends on the implementation used, so should
+not be relied upon, but is something to be aware of when making use of object
+identity tests.
+However, after ``c = []; d = []``, *c* and *d* are guaranteed to refer to two
+different, unique, newly created empty lists. (Note that ``e = f = []`` assigns
+the *same* object to both *e* and *f*.)
 
 
 .. _types: