[New-bugs-announce] [issue21408] delegation of `!=` to the right-hand side argument is not always done

[Jean-Paul Calderone]

New submission from Jean-Paul Calderone:

$ ~/Projects/cpython/3.4/python -c '
class Foo(object):
    def __ne__(self, other):
        return "yup"
    def __eq__(self, other):
        return "nope"

class Bar(object):
    pass
        
print(object() != Foo(), object() == Foo())
print(Bar() != Foo(), Bar() == Foo())
'
yup nope
False nope
$

The output I would expect from this is

    yup nope
    yup nope

That is, even when the type of the left-hand argument is not a base class of the type of the right-hand argument, delegation to the right-hand argument is sensible if the left-hand argument does not implement the comparison.

Note that the output also demonstrates that this is already the behavior for `==`.  Only `!=` seems to suffer from this issue.

----------
components: Interpreter Core
messages: 217699
nosy: exarkun
priority: normal
severity: normal
status: open
title: delegation of `!=` to the right-hand side argument is not always done
type: behavior
versions: Python 3.3, Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21408>
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