Document pointer comparison in PyObject_RichCompareBool()

[tamuhey]

BPO	41049
Nosy	@rhettinger, @tamuhey
PRs	bpo-41049: Document pointer comparison in Py_RichCompareBool() #20999

^{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/rhettinger'
closed_at = <Date 2020-06-20.10:13:40.276>
created_at = <Date 2020-06-20.09:20:57.016>
labels = ['type-feature', '3.8', '3.9', '3.10', 'docs']
title = 'Document pointer comparison in PyObject_RichCompareBool()'
updated_at = <Date 2020-06-20.10:28:45.964>
user = 'https://github.com/tamuhey'

bugs.python.org fields:

activity = <Date 2020-06-20.10:28:45.964>
actor = 'tamuhey'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2020-06-20.10:13:40.276>
closer = 'rhettinger'
components = ['Documentation']
creation = <Date 2020-06-20.09:20:57.016>
creator = 'tamuhey'
dependencies = []
files = []
hgrepos = []
issue_num = 41049
keywords = ['patch']
message_count = 4.0
messages = ['371927', '371928', '371930', '371931']
nosy_count = 2.0
nosy_names = ['rhettinger', 'tamuhey']
pr_nums = ['20999']
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41049'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[tamuhey]

Applying PyObject_RichCompareBool to two nans can be true if the two nans are same object, i.e.

a = float("nan")
PyObject_RichCompareBool(a, a, Py_EQ) // True

I read the document (https://docs.python.org/3/c-api/object.html?highlight=pyobject_richcomparebool#c.PyObject_RichCompareBool) and understood it is intended, but there should be gentle comment to tell users this behaviour.

[rhettinger]

Thanks for the report. I'll add a note to the C API docs.

[rhettinger]

Hmm, I missed it. There is already a note in the link you provided"

"""Note If o1 and o2 are the same object, PyObject_RichCompareBool() will always return 1 for Py_EQ and 0 for Py_NE."""