[issue35165] Possible wrong method name in attribute references doc

[Cheryl Sabella]

Cheryl Sabella  added the comment:

> Or maybe just link to 
> https://docs.python.org/3/reference/datamodel.html#object.__getattr__ (which 
> mention about it) will be enough.

In section 6.3.1, __getattr__() is already linked to the datamodel page 
referenced.  

As your suggested change is already in the docs, I'm going to close this.

--
nosy: +cheryl.sabella
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue35165] Possible wrong method name in attribute references doc

[Denis Osipov]

Denis Osipov  added the comment:

Got it.

But now docs says that overriding the __getattr__() method is enough to 
customize attribute access. It's not completely true.

If I understand it correct, to make __getattr__() work every time you need to 
call it by __getattribute__ or raise AttributeError, e.g. store attributes 
somewhere not in instance __dict__. In this case you need to override 
__setattr__ too.

class MyGetattrClass:
def __init__(self):
super().__setattr__("attrs", {})

def __setattr__(self, name, value):
self.attrs[name] = value

def __getattr__(self, name):
try:
print(f"{name} equals {self.attrs[name]}")
except KeyError:
raise AttributeError(
f"{type(self).__name__!r} object has no attribute {name!r}"
) from None

If it's correct, we probably should add some clarification in expressions doc. 
Or maybe just link to 
https://docs.python.org/3/reference/datamodel.html#object.__getattr__ (which 
mention about it) will be enough.

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[issue35165] Possible wrong method name in attribute references doc

[Steven D'Aprano]

Steven D'Aprano  added the comment:

https://docs.python.org/3/reference/expressions.html#attribute-references

__getattr__ is the correct method to override in most (but not all) cases. I 
don't think we should encourage people to override __getattribute__ as the 
first resort.

__getattribute__ is a more specialised method that is used by the interpreter 
at a deeper level. It is called on every attribute access, so it ought to be as 
fast as possible, while __getattr__ is only called if the named attribute 
doesn't exist.

I don't think anything needs to change here.

--
nosy: +steven.daprano

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[issue35165] Possible wrong method name in attribute references doc

[Denis Osipov]

New submission from Denis Osipov :

6.3.1. Attribute references says:

"The primary must evaluate to an object of a type that supports attribute 
references, which most objects do. This object is then asked to produce the 
attribute whose name is the identifier. This production can be customized by 
overriding the __getattr__() method. If this attribute is not available, the 
exception AttributeError is raised."

It seems that __getattribute__ method is meaning.

--
assignee: docs@python
components: Documentation
messages: 329245
nosy: denis-osipov, docs@python
priority: normal
severity: normal
status: open
title: Possible wrong method name in attribute references doc
type: behavior
versions: Python 3.4, Python 3.5, Python 3.6, Python 3.7, Python 3.8

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