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'value' attribute for ValueError #62366

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brettcannon opened this issue Jun 7, 2013 · 5 comments
Closed

'value' attribute for ValueError #62366

brettcannon opened this issue Jun 7, 2013 · 5 comments
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interpreter-core (Objects, Python, Grammar, and Parser dirs) type-feature A feature request or enhancement

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@brettcannon
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BPO 18166
Nosy @warsaw, @brettcannon, @pitrou, @ezio-melotti

Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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GitHub fields:

assignee = None
closed_at = <Date 2015-04-14.22:09:41.854>
created_at = <Date 2013-06-07.20:56:56.703>
labels = ['interpreter-core', 'type-feature']
title = "'value' attribute for ValueError"
updated_at = <Date 2015-04-14.22:09:41.852>
user = 'https://github.com/brettcannon'

bugs.python.org fields:

activity = <Date 2015-04-14.22:09:41.852>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2015-04-14.22:09:41.854>
closer = 'pitrou'
components = ['Interpreter Core']
creation = <Date 2013-06-07.20:56:56.703>
creator = 'brett.cannon'
dependencies = []
files = []
hgrepos = []
issue_num = 18166
keywords = []
message_count = 5.0
messages = ['190781', '228594', '240945', '241033', '241042']
nosy_count = 7.0
nosy_names = ['barry', 'brett.cannon', 'pitrou', 'ezio.melotti', 'cvrebert', 'BreamoreBoy', 'blackfawn']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue18166'
versions = ['Python 3.5']
@brettcannon
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A 'value attribute for ValueError could store a weakref to the value which triggered the exception. It should be a weakref so at to prevent accidental prevention of GC of the value.

@brettcannon brettcannon added interpreter-core (Objects, Python, Grammar, and Parser dirs) type-feature A feature request or enhancement labels Jun 7, 2013
@BreamoreBoy
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BreamoreBoy mannequin commented Oct 5, 2014

Just a gentle reminder guys.

@blackfawn
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blackfawn mannequin commented Apr 14, 2015

There's actually no advantage for a weakref here, since the exception object already holds an indirect reference to all the raising frame's locals through __traceback__.

@blackfawn
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blackfawn mannequin commented Apr 14, 2015

So, this is actually impossible to do.
Since exceptions are c-level classes, adding members to ValueError means anything that multiple-inherits from ValueError and any other complex exception gets a multiple bases layout conflict. There's already one such class - _pyio.UnsupportedOperation inherits both ValueError and OSError - but the bigger issue is that this would break compatibility.

After discussing it (face-to-face) with a bunch of core devs, I think the only reasonable course of action is to close the issue and never speak of this again.

@pitrou
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pitrou commented Apr 14, 2015

Thanks for the analysis. Closing then!

@pitrou pitrou closed this as completed Apr 14, 2015
@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
This was referenced Oct 5, 2022
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