Difference in equality check between C and Python implementation for datetime module's timedelta and time

[tirkarthi]

BPO	37579
Nosy	@abalkin, @serhiy-storchaka, @pganssle, @miss-islington, @tirkarthi
PRs	bpo-37579: Return NotImplemented in Python implementation of __eq__ to match C implementation of datetime for timedelta and time #14726 [3.8] bpo-37579: Improve equality behavior for pure Python datetime and time (GH-14726) #14743 [3.7] bpo-37579: Improve equality behavior for pure Python datetime and time (GH-14726) #14745

^{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 2019-07-14.10:04:38.808>
created_at = <Date 2019-07-13.05:25:41.676>
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = "Difference in equality check between C and Python implementation for datetime module's timedelta and time"
updated_at = <Date 2019-07-25.21:16:37.867>
user = 'https://github.com/tirkarthi'

bugs.python.org fields:

activity = <Date 2019-07-25.21:16:37.867>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2019-07-14.10:04:38.808>
closer = 'p-ganssle'
components = ['Library (Lib)']
creation = <Date 2019-07-13.05:25:41.676>
creator = 'xtreak'
dependencies = []
files = []
hgrepos = []
issue_num = 37579
keywords = ['patch']
message_count = 6.0
messages = ['347773', '347813', '347815', '347821', '347903', '348454']
nosy_count = 5.0
nosy_names = ['belopolsky', 'serhiy.storchaka', 'p-ganssle', 'miss-islington', 'xtreak']
pr_nums = ['14726', '14743', '14745']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37579'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[tirkarthi]

As reported by Serhiy on https://bugs.python.org/issue37555#msg347733 there is a difference in __eq__ definition in datetime module's C and Python implementation for timedelta and time. When the other in __eq__ is not of the same type NotImplemented is not returned in Python implementation like C causing equality to behave differently.

Difference in C implementation and Python implementation for datetime.timedelta.__eq__

cpython/Modules/_datetimemodule.c

Line 2152 in c8e7146

static PyObject *

static PyObject *
delta_richcompare(PyObject *self, PyObject *other, int op)
{
    if (PyDelta_Check(other)) {
        int diff = delta_cmp(self, other);
        return diff_to_bool(diff, op);
    }
    else {
        Py_RETURN_NOTIMPLEMENTED;
    }
}

cpython/Lib/datetime.py

Line 732 in c8e7146

def __eq__(self, other):

def __eq__(self, other):
    if isinstance(other, timedelta):
        return self._cmp(other) == 0
    else:
        return False

I will add a PR for this with test.

[serhiy-storchaka]

Do you mind to fix also other similar cases if they are? __lt__ and others should have the same property.

[pganssle]

New changeset e6b46aa by Paul Ganssle (Xtreak) in branch 'master':
bpo-37579: Improve equality behavior for pure Python datetime and time (GH-14726)
e6b46aa

[miss-islington]

New changeset 143672c by Miss Islington (bot) in branch '3.8':
bpo-37579: Improve equality behavior for pure Python datetime and time (GH-14726)
143672c

[miss-islington]

New changeset c6b3106 by Miss Islington (bot) (Xtreak) in branch '3.7':
[3.7] bpo-37579: Improve equality behavior for pure Python datetime and time (GH-14726) (GH-14745)
c6b3106

[serhiy-storchaka]

See bpo-37685.