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bpo-12634: Clarify an awkward section of the tutorial #15406

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20 changes: 14 additions & 6 deletions Doc/tutorial/classes.rst
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Expand Up @@ -475,12 +475,20 @@ Random Remarks

.. These should perhaps be placed more carefully...

Data attributes override method attributes with the same name; to avoid
accidental name conflicts, which may cause hard-to-find bugs in large programs,
it is wise to use some kind of convention that minimizes the chance of
conflicts. Possible conventions include capitalizing method names, prefixing
data attribute names with a small unique string (perhaps just an underscore), or
using verbs for methods and nouns for data attributes.
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Wow. At first I was confused. If one defines module, class, or instance attributes with the same name, the second wins. Then the first two advice items are wrong, the third correct, but misses the realistic case of noun data attribute duplication on class and instance. Your example covers that nicely. Please apply and backport.

If the same attribute name occurs in both an instance and in a class,
then attribute lookup prioritizes the instance::

>>> class Warehouse:
purpose = 'storage'
region = 'west'

>>> w1 = Warehouse()
>>> print(w1.purpose, w1.region)
storage west
>>> w2 = Warehouse()
>>> w2.region = 'east'
>>> print(w2.purpose, w2.region)
storage east

Data attributes may be referenced by methods as well as by ordinary users
("clients") of an object. In other words, classes are not usable to implement
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