gh-119016: Remove outdated sentences from the "classes" tutorial

[nineteendo]

• Issue: Classes tutorial: confusing explanation of non-instance methods #119016

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📚 Documentation preview 📚: https://cpython-previews--119130.org.readthedocs.build/

[eendebakpt]

I am still wondering why the text "not referring to..." is needed here. There are some differences between class instance methods and builtin class instance methods (e.g. alist.append does not have a __func__ attribute, the type is different), but those differences are not mentioned in the text below.

[nineteendo]

https://docs.python.org/3/tutorial/classes.html#odds-and-ends:

Instance method objects have attributes, too: m.__self__ is the instance object with the method m(), and m.__func__ is the function object corresponding to the method.

[AlexWaygood]

This paragraph is very old. It appears to have remained in this tutorial largely unchanged since it was originally added in 1992, in 5e0759d.

I don't think that the original purpose of this paragraph was to point out that alist.append has, strictly speaking, a slightly different type to a user-defined method on a user-defined class. That feels like a subtle point that leads to few visible differences in behaviour for users.

In very early versions of Python, many builtin types such as list were not classes at all -- they were more primitive types that operated according to a different object model. (See https://stackoverflow.com/a/54873/13990016 for more details. This changed in Python 2.2, originally released in 2001.) I think this paragraph was originally intended to clarify that even objects that were not instances of classes, such as lists, could also have methods.

Nowadays, all objects are instances of classes, and it is not possible to create types that do not inherit from object. It's been this way for a long time now. As such, I think this paragraph is now largely redundant. Rather than making the edit you propose here, I would simply delete most of this paragraph altogether.

Suggested change

	The other kind of instance attribute reference is a *method*. In the following
	discussion, we’ll use the term method exclusively to mean methods of class
	instance objects, unless explicitly stated otherwise. (In other words, we are
	not referring to built-in methods such as ``alist.append`` where ``alist`` is
	a :class:`list` object.)
	The other kind of instance attribute reference is a *method*. A method is a
	function that "belongs to" an object.

[deuberger]

I thought about suggesting this originally, but https://docs.python.org/3/reference/datamodel.html#built-in-methods makes it sound like there's still some difference between built-in methods and methods on user defined classes (besides built-ins being defined in C that is). As mentioned in #119016 (comment), the types are different at least.

Does the last paragraphs in particular of both 9.3.4 (https://docs.python.org/3/tutorial/classes.html#method-objects) and 9.7 (https://docs.python.org/3/tutorial/classes.html#odds-and-ends) apply equally to built-in methods? If not, there might still be some confusion.

[AlexWaygood]

Yes, builtin methods are a different type to pure-Python methods, but they're meant to be entirely duck-type compatible. Any glaring differences between them are arguably bugs. Off the top of my head, I don't think any of the paragraphs you link to there are different when it comes to builtin methods.

[AlexWaygood]

Thanks!

[bedevere-app]

GH-119925 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-119926 is a backport of this pull request to the 3.12 branch.