#30651: Model.__eq__ never returns NotImplemented
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Reporter: Elizabeth | Owner: Elizabeth Uselton
Uselton |
Type: Bug | Status: assigned
Component: Database | Version: 2.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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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>
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