Make __sizeof__ for builtin types more subclass friendly

[serhiy-storchaka]

BPO	25421
Nosy	@pitrou, @bitdancer, @serhiy-storchaka
Files	sizeof_dynamic.patch

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

Show more details

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-12-20.07:27:55.452>
created_at = <Date 2015-10-16.16:42:00.760>
labels = ['extension-modules', 'interpreter-core', 'type-bug']
title = 'Make __sizeof__ for builtin types more subclass friendly'
updated_at = <Date 2015-12-20.07:27:55.451>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-12-20.07:27:55.451>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-12-20.07:27:55.452>
closer = 'serhiy.storchaka'
components = ['Extension Modules', 'Interpreter Core']
creation = <Date 2015-10-16.16:42:00.760>
creator = 'serhiy.storchaka'
dependencies = []
files = ['40795']
hgrepos = []
issue_num = 25421
keywords = ['patch']
message_count = 6.0
messages = ['253074', '256734', '256735', '256737', '256738', '256739']
nosy_count = 4.0
nosy_names = ['pitrou', 'r.david.murray', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25421'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

[serhiy-storchaka]

Default __sizeof__() implementation uses tp_basicsize. This makes it to work correctly with most builtin types and types with __slots__ (using __slots__ increases tp_basicsize). But special implementations of __sizeof__() use static object size ('sizeof(XXXObject)'), and return incorrect result for subclasses that increase tp_basicsize. Proposed patch makes __sizeof__() for all subclassable builtin type that support changing object size (i.e. tp_itemsize == 0) to use dynamic size _PyObject_SIZE(Py_TYPE(self)).

Example (with patched code):
>>> class D(dict):
...     __slots__ = 'a', 'b', 'c'
... 
>>> sys.getsizeof({})
144
>>> sys.getsizeof(D())
156

In unpatched Python sys.getsizeof(D()) returns 144.

[python-dev]

New changeset 71d6755145ae by Serhiy Storchaka in branch '3.5':
Issue bpo-25421: __sizeof__ methods of builtin types now use dynamic basic size.
https://hg.python.org/cpython/rev/71d6755145ae

New changeset 4a47e998c40a by Serhiy Storchaka in branch 'default':
Issue bpo-25421: __sizeof__ methods of builtin types now use dynamic basic size.
https://hg.python.org/cpython/rev/4a47e998c40a

New changeset be3998aed1e7 by Serhiy Storchaka in branch '2.7':
Issue bpo-25421: __sizeof__ methods of builtin types now use dynamic basic size.
https://hg.python.org/cpython/rev/be3998aed1e7

[serhiy-storchaka]

Committed with improved tests.

[bitdancer]

At least some of the buildbots aren't happy.

http://buildbot.python.org/all/builders/ARMv7%20Ubuntu%203.5/builds/479/steps/test/logs/stdio

http://buildbot.python.org/all/builders/ARMv7%20Ubuntu%202.7/builds/1077/steps/test/logs/stdio

http://buildbot.python.org/all/builders/AMD64%20FreeBSD%209.x%202.7/builds/1098/steps/test/logs/stdio

[python-dev]

New changeset a1388dbdd293 by Serhiy Storchaka in branch '3.5':
Use correct PyGC_Head size in tests for issue bpo-25421.
https://hg.python.org/cpython/rev/a1388dbdd293

New changeset ab97ff838e11 by Serhiy Storchaka in branch '2.7':
Use correct PyGC_Head size in tests for issue bpo-25421.
https://hg.python.org/cpython/rev/ab97ff838e11

New changeset 5115f39cc59f by Serhiy Storchaka in branch 'default':
Use correct PyGC_Head size in tests for issue bpo-25421.
https://hg.python.org/cpython/rev/5115f39cc59f

[serhiy-storchaka]

Thank you David. Looks related to alignment. Hope this will help.