Making weakref.ref subclassable

[freddrake]

BPO	983019
Nosy	@freddrake
Files	subclassable-weakrefs.patch: Patch to make weakref.ref a subclassable new-style type subclassable-weakref-docs.patch: Documentation 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 = None
closed_at = <Date 2004-07-02.19:02:06.000>
created_at = <Date 2004-06-30.21:04:51.000>
labels = ['interpreter-core']
title = 'Making weakref.ref subclassable'
updated_at = <Date 2004-07-02.19:02:06.000>
user = 'https://github.com/freddrake'

bugs.python.org fields:

activity = <Date 2004-07-02.19:02:06.000>
actor = 'fdrake'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2004-06-30.21:04:51.000>
creator = 'fdrake'
dependencies = []
files = ['6066', '6067']
hgrepos = []
issue_num = 983019
keywords = ['patch']
message_count = 3.0
messages = ['46285', '46286', '46287']
nosy_count = 1.0
nosy_names = ['fdrake']
pr_nums = []
priority = 'high'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue983019'
versions = ['Python 2.4']

[freddrake]

This patch makes weak references subclassable. This
includes the following changes:

• weakref.ref and weakref.ReferenceType will become
  aliases for each other

• weakref.ref will be a modern, new-style class with
  proper __new__ and __init__ methods

• weakref.WeakValueDictionary will have a lighter
  memory footprint, using a new weakref.ref subclass to
  associate the key with the value, allowing us to have
  only a single object of overhead for each dictionary
  entry (currently, there are 3 objects of overhead per
  entry: a weakref to the value, a weakref to the
  dictionary, and a function object used as a weakref
  callback; the weakref to the dictionary could be
  avoided without this change)

• a new macro, PyWeakref_CheckRefExact(), will be added

• PyWeakref_CheckRef() will check for subclasses of
  weakref.ref

• the cyclic garbage detector will be affected by the
  change to PyWeakref_CheckRef(); it will potentially
  call issubtype() for objects in the unreachable list
  that do not have finalizers (in the
  move_troublemakers() function). This should only
  happen for weakref objects which are not of one of the
  "standard" three types (ref, proxy, and callable
  proxy). For debug builds, it will also affect
  assertions in the clear_weakerfs() and
  release_weakrefs() functions.

The change to the cyclic garbage detector probably
carries the most risk, and that only because the
potential for a performance penalty. Running the Zope
3 test suite did not show any clear change in
performance, and a key subsystem in Zope
(zope.interface) uses weakrefs extensively.

[freddrake]

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user_id=3066

Added LaTeX documentation as a separate patch.

[freddrake]

Logged In: YES
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Committed for Python 2.4:

Doc/lib/libweakref.tex 1.27
Include/weakrefobject.h 1.5
Lib/test/test_weakref.py 1.41
Lib/weakref.py 1.23
Misc/NEWS 1.1020
Modules/_weakref.c 1.19
Objects/object.c 2.219
Objects/weakrefobject.c 1.17