Expose default __getstate__ and __setstate__

[youkaichao]

BPO	41547
Nosy	@serhiy-storchaka, @youkaichao
Superseder	bpo-26579: Support pickling slots in subclasses of common classes

^{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 2020-08-14.06:25:45.652>
created_at = <Date 2020-08-14.04:57:50.619>
labels = ['type-bug']
title = 'Expose default __getstate__ and __setstate__'
updated_at = <Date 2020-08-14.06:25:45.649>
user = 'https://github.com/youkaichao'

bugs.python.org fields:

activity = <Date 2020-08-14.06:25:45.649>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-08-14.06:25:45.652>
closer = 'serhiy.storchaka'
components = []
creation = <Date 2020-08-14.04:57:50.619>
creator = 'youkaichao'
dependencies = []
files = []
hgrepos = []
issue_num = 41547
keywords = []
message_count = 2.0
messages = ['375369', '375372']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'youkaichao']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '26579'
type = 'behavior'
url = 'https://bugs.python.org/issue41547'
versions = []

[youkaichao]

According to the doc ( https://docs.python.org/3/library/pickle.html#object.\_\_getstate__ ), an object may not have a __getstate__ method.

During pickling and unpickling, python first finds getstate and setstate, which may invoke a customed getattr. I think this is unnecessary if python just provides a default implementation for getstate / setstate . An additional benefit of this is that setstate and getstate becomes available for every object and it is possible to do something like getstate(obj).

For people who customize getattr, I think no one intends to deal with obj.__getattr__（“__getstate__”）, so it makes sense not to invoke __getattr__ during pickling and unpickling.

[serhiy-storchaka]

This is virtually a duplicate of isssue26579.