[New-bugs-announce] [issue45198] __set_name__ documentation not clear about its usage with non-descriptor classes

[xitop]

New submission from xitop <reg.bugs at poti.sk>:

The object.__set_name__() function (introduced in Python 3.6 by PEP-487) is mentioned in the "what's new " summary as an extension to the descriptor protocol [1] and documented in the "implementing descriptors" section [2].

However, the PEP itself states that it "adds an __set_name__ initializer for class attributes, especially if they are descriptors.". And it indeed works for plain classes where the descriptor protocol is not used at all (no __get__ or __set__ or __delete__):

----
class NotDescriptor:
    def __set_name__(self, owner, name):
        print('__set_name__ called')
            
class SomeClass:
    attr = NotDescriptor()
----

It is clear that this method is helpful when used in descriptors and that is its intended use, but other valid use-cases probably exist.

I suggest to amend the documentation to clarify that (correct me if I'm wrong) the __set_name__ is called for every class used as an attribute in an other class, not only for descriptors.

---

URLs:

[1]: https://docs.python.org/3/whatsnew/3.6.html#pep-487-descriptor-protocol-enhancements

[2]: https://docs.python.org/3/reference/datamodel.html#implementing-descriptors

----------
assignee: docs at python
components: Documentation
messages: 401785
nosy: docs at python, xitop
priority: normal
severity: normal
status: open
title: __set_name__ documentation not clear about its usage with non-descriptor classes
versions: Python 3.6, Python 3.7, Python 3.8, Python 3.9

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<https://bugs.python.org/issue45198>
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