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gh-122511: Improve documentation for object identity of mutable/immutable types (#122512) 

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
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Bénédikt Tran 2024-08-07 15:40:19 +02:00 committed by GitHub
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Doc/reference/datamodel.rst
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@ -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: