Fixed #30651 -- Made __eq__() methods return NotImplemented for not implemented comparisons.

Changed __eq__ to return NotImplemented instead of False if compared to
an object of the same type, as is recommended by the Python data model
reference. Now these models can be compared to ANY (or other objects
with __eq__ overwritten) without returning False automatically.

6 files changed, 22 insertions, 16 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 0b8425aa85..0a5e5ff673 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -522,7 +522,7 @@ class Model(metaclass=ModelBase):
 
     def __eq__(self, other):
         if not isinstance(other, Model):
-            return False
+            return NotImplemented
         if self._meta.concrete_model != other._meta.concrete_model:
             return False
         my_pk = self.pk
diff --git a/django/db/models/constraints.py b/django/db/models/constraints.py
index e7f81d3ee9..fe0d42a168 100644
--- a/django/db/models/constraints.py
+++ b/django/db/models/constraints.py
@@ -54,11 +54,9 @@ class CheckConstraint(BaseConstraint):
         return "<%s: check='%s' name=%r>" % (self.__class__.__name__, self.check, self.name)
 
     def __eq__(self, other):
-        return (
-            isinstance(other, CheckConstraint) and
-            self.name == other.name and
-            self.check == other.check
-        )
+        if isinstance(other, CheckConstraint):
+            return self.name == other.name and self.check == other.check
+        return super().__eq__(other)
 
     def deconstruct(self):
         path, args, kwargs = super().deconstruct()
@@ -106,12 +104,13 @@ class UniqueConstraint(BaseConstraint):
         )
 
     def __eq__(self, other):
-        return (
-            isinstance(other, UniqueConstraint) and
-            self.name == other.name and
-            self.fields == other.fields and
-            self.condition == other.condition
-        )
+        if isinstance(other, UniqueConstraint):
+            return (
+                self.name == other.name and
+                self.fields == other.fields and
+                self.condition == other.condition
+            )
+        return super().__eq__(other)
 
     def deconstruct(self):
         path, args, kwargs = super().deconstruct()
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index 2b59dd301a..5df765b626 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -401,7 +401,9 @@ class BaseExpression:
         return tuple(identity)
 
     def __eq__(self, other):
-        return isinstance(other, BaseExpression) and other.identity == self.identity
+        if not isinstance(other, BaseExpression):
+            return NotImplemented
+        return other.identity == self.identity
 
     def __hash__(self):
         return hash(self.identity)
diff --git a/django/db/models/indexes.py b/django/db/models/indexes.py
index b156366764..49f4989462 100644
--- a/django/db/models/indexes.py
+++ b/django/db/models/indexes.py
@@ -112,4 +112,6 @@ class Index:
         )
 
     def __eq__(self, other):
-        return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
+        if self.__class__ == other.__class__:
+            return self.deconstruct() == other.deconstruct()
+        return NotImplemented
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 4417c17592..794e0faae7 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -1543,7 +1543,9 @@ class Prefetch:
         return None
 
     def __eq__(self, other):
-        return isinstance(other, Prefetch) and self.prefetch_to == other.prefetch_to
+        if not isinstance(other, Prefetch):
+            return NotImplemented
+        return self.prefetch_to == other.prefetch_to
 
     def __hash__(self):
         return hash((self.__class__, self.prefetch_to))
diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py
index 7a667814f4..189fb4fa44 100644
--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -309,8 +309,9 @@ class FilteredRelation:
         self.path = []
 
     def __eq__(self, other):
+        if not isinstance(other, self.__class__):
+            return NotImplemented
         return (
-            isinstance(other, self.__class__) and
             self.relation_name == other.relation_name and
             self.alias == other.alias and
             self.condition == other.condition