bisect insort C implementation ignores methods on list subclasses

[jek]

BPO	3935
Nosy	@birkenfeld, @rhettinger, @amauryfa
Files	test.py: test case bisect.diff: Patch bisect2.patch: Patch with PyList_CheckExact

^{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/birkenfeld'
closed_at = <Date 2008-10-08.18:47:48.025>
created_at = <Date 2008-09-22.18:53:44.168>
labels = ['type-bug', 'library']
title = 'bisect insort C implementation ignores methods on list subclasses'
updated_at = <Date 2008-10-08.18:47:48.023>
user = 'https://bugs.python.org/jek'

bugs.python.org fields:

activity = <Date 2008-10-08.18:47:48.023>
actor = 'georg.brandl'
assignee = 'georg.brandl'
closed = True
closed_date = <Date 2008-10-08.18:47:48.025>
closer = 'georg.brandl'
components = ['Library (Lib)']
creation = <Date 2008-09-22.18:53:44.168>
creator = 'jek'
dependencies = []
files = ['11561', '11614', '11623']
hgrepos = []
issue_num = 3935
keywords = ['patch']
message_count = 6.0
messages = ['73589', '73867', '73873', '73881', '74348', '74543']
nosy_count = 5.0
nosy_names = ['georg.brandl', 'rhettinger', 'hdima', 'amaury.forgeotdarc', 'jek']
pr_nums = []
priority = 'low'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue3935'
versions = ['Python 3.0', 'Python 2.7']

[jek]

The C implementation (only) of bisect does not invoke list subclass
methods when insorting. Code like this will not trigger the assert:

  class Boom(list):
     def insert(self, index, item):
         assert False

bisect.insort(Boom(), 123)

object-derived classes are OK.

[hdima]

Actually it was an optimization. PyList_Insert() was used for list and
list-derived objects.

I've attached the patch which fix the issue and for me the new code
looks even cleaner than the original code.

[amauryfa]

We could keep the optimization for the standard case:
What about simply replacing PyList_Check with PyList_CheckExact?

• most usages use plain lists, and will even run slightly faster
• list-derived objects get the desired behaviour.

[hdima]

Good idea! Don't know why I didn't use it in the very first version. :-)

New patch attached.

[rhettinger]

Don't think this is too late for Py3.0.

[birkenfeld]

OK, committed as r66856, should get merged to 3.0 soon.