Pickle nested names with protocols < 4

[serhiy-storchaka]

BPO	23611
Nosy	@pitrou, @vstinner, @avassalotti, @serhiy-storchaka
Files	pickle_nested_names_2.patch

^{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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-03-31.16:49:01.881>
created_at = <Date 2015-03-08.17:50:40.420>
labels = ['type-feature', 'library']
title = 'Pickle nested names with protocols < 4'
updated_at = <Date 2015-03-31.16:49:01.881>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-03-31.16:49:01.881>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-03-31.16:49:01.881>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-03-08.17:50:40.420>
creator = 'serhiy.storchaka'
dependencies = []
files = ['38393']
hgrepos = []
issue_num = 23611
keywords = ['patch']
message_count = 9.0
messages = ['237548', '237567', '237568', '239362', '239364', '239368', '239389', '239683', '239711']
nosy_count = 5.0
nosy_names = ['pitrou', 'vstinner', 'alexandre.vassalotti', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue23611'
versions = ['Python 3.5']

[serhiy-storchaka]

Proposed patch allows Python implementation of the pickle module to pickle nested names (e.g. methods) with protocols < 4. Pickled data is compatible with old releases.

If this is good I'll write C implementation.

[serhiy-storchaka]

Fixed few bugs and added C implementation.

[pitrou]

Interesting. I have only skimmed through the patch, but +1 on the principle.

[vstinner]

Hum, I don't know well the pickle module. Is it backward compatible? Should Python 2 be able to unserialize data serialized by Python 3? If yes, can you patch break this compatibility?

It is unclear to me if it makes sense to even modify protocols different than the latest version.

[serhiy-storchaka]

Pickle is backward compatible and Python 2 usually is able to unpickle data pickled by Python 3 with protocol < 3. The patch doesn't break compatibility. Current default protocol is 3 for compatibility with older Python 3 versions. It is used in multiprocessing and this is not configurable.

[vstinner]

It is used in multiprocessing and this is not configurable.

Oh, it would be nice to switch to version 4 by default, or make it
configurable. I read that the version 4 is faster.

[serhiy-storchaka]

bpo-23403. But looks it is early yet for this.

Note that this patch doesn't modify protocols. It just makes the pickler more smart and able to serialize more objects with existing protocols. It is the same as add pickle support for some type that didn't support the pickling before.

[python-dev]

New changeset ca12465418bd by Serhiy Storchaka in branch 'default':
Issue bpo-23611: Serializing more "lookupable" objects (such as unbound methods
https://hg.python.org/cpython/rev/ca12465418bd

[python-dev]

New changeset f78b9f700d45 by Serhiy Storchaka in branch 'default':
Issue bpo-23611: Fixed enums pickling tests. Now all picklings work with all
https://hg.python.org/cpython/rev/f78b9f700d45