pickle documentation says that unpickling may not call __new__

[tifv]

BPO	27635
Nosy	@avassalotti, @tifv, @serhiy-storchaka, @miss-islington, @furkanonder, @iritkatriel
PRs	bpo-27635: Fix pickle documentation about __new__ not being called. #19269 [3.8] bpo-27635: Fix pickle documentation about __new__ not being called. (GH-19269) #19585 [3.7] bpo-27635: Fix pickle documentation about __new__ not being called. (GH-19269) #19586

^{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 2020-10-11.20:22:32.477>
created_at = <Date 2016-07-27.17:07:25.666>
labels = ['type-bug', '3.7', 'docs']
title = 'pickle documentation says that unpickling may not call __new__'
updated_at = <Date 2020-10-11.20:22:32.477>
user = 'https://github.com/tifv'

bugs.python.org fields:

activity = <Date 2020-10-11.20:22:32.477>
actor = 'alexandre.vassalotti'
assignee = 'docs@python'
closed = True
closed_date = <Date 2020-10-11.20:22:32.477>
closer = 'alexandre.vassalotti'
components = ['Documentation']
creation = <Date 2016-07-27.17:07:25.666>
creator = 'july'
dependencies = []
files = []
hgrepos = []
issue_num = 27635
keywords = ['patch']
message_count = 7.0
messages = ['271465', '365442', '366730', '366731', '366732', '366950', '378451']
nosy_count = 7.0
nosy_names = ['alexandre.vassalotti', 'july', 'docs@python', 'serhiy.storchaka', 'miss-islington', 'furkanonder', 'iritkatriel']
pr_nums = ['19269', '19585', '19586']
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27635'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[tifv]

A note just below object.__setstate__() documentation
https://docs.python.org/3.6/library/pickle.html#object.\_\_setstate__
says that
"""
… the type should implement __getnewargs__() or __getnewargs_ex__() to establish such an invariant; otherwise, neither __new__() nor __init__() will be called.
"""

I believe that note about not calling __new__() was relevant in python2. I could not find case in python3 in which __new__() would not be called. And __init__() is not called anyway, as far as I understand (unless explicitly by __setstate__() or something).

Python 3.6.0a3+ (default:da9898e7e90d, Jul 27 2016, 19:51:12) 
[GCC 4.9.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class C:
...   def __getstate__(self): return {'foo' : self.foo}
...   def __setstate__(self, state): self.foo = state['foo']
...   def __new__(cls):
...     print('__new__ is called'); return super().__new__(cls)
...   def __init__(self):
...     print('__init__ is called'); self.foo = None; super().__init__()
... 
>>> c = C(); c.foo = 'bar'
__new__ is called
__init__ is called
>>> import pickle
>>> c2 = pickle.loads(pickle.dumps(c))
__new__ is called
>>> c2.foo
'bar'

[furkanonder]

There is still an mistake in the document. I sent a pr to fix it.

[miss-islington]

New changeset 482259d by Furkan Önder in branch 'master':
bpo-27635: Fix pickle documentation about __new__ not being called. (GH-19269)
482259d

[miss-islington]

New changeset 0abb548 by Miss Islington (bot) in branch '3.7':
bpo-27635: Fix pickle documentation about __new__ not being called. (GH-19269)
0abb548

[miss-islington]

New changeset 020f2aa by Miss Islington (bot) in branch '3.8':
bpo-27635: Fix pickle documentation about __new__ not being called. (GH-19269)
020f2aa

[furkanonder]

The problem is fixed, issue can be closed.

[iritkatriel]

Ping (to close the issue).