#30651: Model.__eq__ never returns NotImplemented
-------------------------------------+-------------------------------------
Reporter: Elizabeth Uselton | Owner: Elizabeth
| Uselton
Type: Bug | Status: assigned
Component: Database layer | Version: 2.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by Elizabeth Uselton:
Old description:
> Model.__eq__ never returns NotImplemented if it encounters an object it
> doesn't know how to compare against. Instead, if the object it is
> comparing to is not a Django Model, it automatically returns False.
>
> https://github.com/django/django/blob/master/django/db/models/base.py#L526
>
> According to the Python 3 data model reference, a __eq__ should return
> NotImplemented
> https://docs.python.org/3/reference/datamodel.html#object.__eq__
> If a.__eq__(b) returns NotImplemented, then b.__eq__(a) will be tried. If
> both return NotImplemented, then an is check is performed, and if that
> fails it returns False.
>
> This may seem like a relatively innocuous difference, but it can cause
> some nasty bugs. The most obvious is that for testing,
> <A Django Model> == mock.ANY returns False, since by not returning
> NotImplemented it never even looks at the overridden __eq__ on ANY.
New description:
`Model.__eq__` never returns NotImplemented if it encounters an object it
doesn't know how to compare against. Instead, if the object it is
comparing to is not a Django Model, it automatically returns False.
`https://github.com/django/django/blob/master/django/db/models/base.py#L526`
According to the Python 3 data model reference, a `__eq__` should return
NotImplemented
`https://docs.python.org/3/reference/datamodel.html#object.__eq__`
If `a.__eq__(b)` returns NotImplemented, then `b.__eq__(a)` will be tried.
If both return NotImplemented, then an is check is performed, and if that
fails it returns False.
This may seem like a relatively innocuous difference, but it can cause
some nasty bugs. The most obvious is that for testing,
<A Django Model> == mock.ANY returns False, since by not returning
NotImplemented it never even looks at the overridden `__eq__` on ANY.
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Ticket URL: <https://code.djangoproject.com/ticket/30651#comment:1>
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