python / python/cpython

unpickling a subclass of list fails when it implements its own extend method

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3.10 3.11 3.7 (EOL) 3.8 (EOL) 3.9 (EOL) extension-modules stdlib type-bug
Dominant language
Python
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Description

BPO 43946
Nosy @gpshead, @serhiy-storchaka, @rickeylev

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 = None
created_at = <Date 2021-04-27.00:33:02.281>
labels = ['3.8', '3.9', 'extension-modules', '3.7', 'type-bug', '3.10', '3.11', 'library']
title = 'unpickling a subclass of list fails when it implements its own extend method'
updated_at = <Date 2021-04-27.16:05:29.529>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2021-04-27.16:05:29.529>
actor = 'gregory.p.smith'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules', 'Library (Lib)']
creation = <Date 2021-04-27.00:33:02.281>
creator = 'gregory.p.smith'
dependencies = []
files = []
hgrepos = []
issue_num = 43946
keywords = ['3.7regression']
message_count = 4.0
messages = ['392008', '392022', '392027', '392100']
nosy_count = 3.0
nosy_names = ['gregory.p.smith', 'serhiy.storchaka', 'richardlev']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43946'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

No files or tests are named in the issue. Start by reproducing the failure with a list subclass that defines its own extend method, then trace the unpickling path and find the relevant library tests. Done means that this subclass can be unpickled successfully without breaking existing list behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
backend
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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