[issue44649] dataclasses slots with init=False field raises AttributeException

[miss-islington]

miss-islington  added the comment:


New changeset 10343bd98390ef15909e3a19f26a6178162996fd by Miss Islington (bot) 
in branch '3.10':
bpo-44649: Fix dataclasses(slots=True) with a field with a default, but 
init=False (GH-29692)
https://github.com/python/cpython/commit/10343bd98390ef15909e3a19f26a6178162996fd


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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Eric V. Smith  added the comment:

Thanks for the bug report!

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Eric V. Smith  added the comment:


New changeset d3062f672c92855b7e9e962ad4bf1a67abd4589b by Eric V. Smith in 
branch 'main':
bpo-44649: Fix dataclasses(slots=True) with a field with a default, but 
init=False (GH-29692)
https://github.com/python/cpython/commit/d3062f672c92855b7e9e962ad4bf1a67abd4589b


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[issue44649] dataclasses slots with init=False field raises AttributeException

[miss-islington]

Change by miss-islington :


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nosy: +miss-islington
nosy_count: 2.0 -> 3.0
pull_requests: +27940
pull_request: https://github.com/python/cpython/pull/29704

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Change by Eric V. Smith :


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versions: +Python 3.11

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Change by Eric V. Smith :


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keywords: +patch
pull_requests: +27930
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/29692

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Christodoulos Tsoulloftas]

Christodoulos Tsoulloftas  added the comment:

Thanks for the update eric, yeah the new error messages are much more 
comprehensive and I am glad to hear the original issue will be addressed as 
well.

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Eric V. Smith  added the comment:

With Pablo's changes, the error now reads (in 3.11):

obj.b
^
AttributeError: 'Example' object has no attribute 'b'

Which is a vast improvement!

I'm working on a PR to initialize obj.b in __init__.

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Eric V. Smith  added the comment:

I created issue 44655 for the confusing error message.

The problem with dataclasses is that the instance variable 'b' needs to be 
initialized, instead of the current dataclasses behavior where it relies on the 
class variable when reading 'b'.

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Eric V. Smith]

Change by Eric V. Smith :


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nosy: +eric.smith

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[issue44649] dataclasses slots with init=False field raises AttributeException

[Christodoulos Tsoulloftas]

New submission from Christodoulos Tsoulloftas :

I am trying the new slots directive but I get an AttributeError when I try to 
access a field with init=False


>>> from dataclasses import dataclass, field
>>> 
>>> @dataclass(slots=True)
... class Example:
... a: str
... b: str = field(default="b", init=False)
... 
>>> obj = Example("a")
>>> obj.__slots__
('a', 'b')
>>> obj.
obj.a  obj.b  
>>> obj.a
'a'
>>> obj.b
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: b. Did you mean: 'b'?
>>> 



❯ python --version
Python 3.10.0b4+

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components: Library (Lib)
messages: 397575
nosy: tefra
priority: normal
severity: normal
status: open
title: dataclasses slots with init=False field raises AttributeException
type: behavior
versions: Python 3.10

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