PYTHON-5596 Fix return type for distinct methods (#2576)

justfile

@@ -58,7 +58,7 @@ lint-manual *args="": && resync
 
 [group('test')]
 test *args="-v --durations=5 --maxfail=10": && resync
-    uvx --extra test pytest {{args}}
+    uv run --extra test pytest {{args}}
 
 [group('test')]
 run-tests *args: && resync

pymongo/asynchronous/collection.py

@@ -3143,7 +3143,7 @@ class AsyncCollection(common.BaseObject, Generic[_DocumentType]):
         comment: Optional[Any] = None,
         hint: Optional[_IndexKeyHint] = None,
         **kwargs: Any,
-    ) -> list[str]:
+    ) -> list[Any]:
         """Get a list of distinct values for `key` among all documents
         in this collection.
 

pymongo/asynchronous/cursor.py

@@ -1063,7 +1063,7 @@ class AsyncCursor(Generic[_DocumentType]):
         """Explicitly close / kill this cursor."""
         await self._die_lock()
 
-    async def distinct(self, key: str) -> list[str]:
+    async def distinct(self, key: str) -> list[Any]:
         """Get a list of distinct values for `key` among all documents
         in the result set of this query.
 

pymongo/synchronous/collection.py

@@ -3136,7 +3136,7 @@ class Collection(common.BaseObject, Generic[_DocumentType]):
         comment: Optional[Any] = None,
         hint: Optional[_IndexKeyHint] = None,
         **kwargs: Any,
-    ) -> list[str]:
+    ) -> list[Any]:
         """Get a list of distinct values for `key` among all documents
         in this collection.
 

pymongo/synchronous/cursor.py

@@ -1061,7 +1061,7 @@ class Cursor(Generic[_DocumentType]):
         """Explicitly close / kill this cursor."""
         self._die_lock()
 
-    def distinct(self, key: str) -> list[str]:
+    def distinct(self, key: str) -> list[Any]:
         """Get a list of distinct values for `key` among all documents
         in the result set of this query.
 

test/test_typing.py

@@ -69,7 +69,7 @@ sys.path[0:0] = [""]
 
 from test import IntegrationTest, PyMongoTestCase, client_context
 
-from bson import CodecOptions, decode, decode_all, decode_file_iter, decode_iter, encode
+from bson import CodecOptions, ObjectId, decode, decode_all, decode_file_iter, decode_iter, encode
 from bson.raw_bson import RawBSONDocument
 from bson.son import SON
 from pymongo import ASCENDING, MongoClient
@@ -141,6 +141,32 @@ class TestPymongo(IntegrationTest):
         docs = to_list(cursor)
         self.assertTrue(docs)
 
+    def test_distinct(self) -> None:
+        self.coll.delete_many({})
+        self.coll.insert_many(
+            [
+                {"_id": None},
+                {"_id": 0},
+                {"_id": ""},
+                {"_id": ObjectId()},
+                {"_id": True},
+            ]
+        )
+
+        def collection_distinct(
+            collection: Collection,
+        ) -> list[None | int | str | ObjectId | bool]:
+            return collection.distinct("_id")
+
+        def cursor_distinct(
+            collection: Collection,
+        ) -> list[None | int | str | ObjectId | bool]:
+            cursor = collection.find()
+            return cursor.distinct("_id")
+
+        collection_distinct(self.coll)
+        cursor_distinct(self.coll)
+
     @only_type_check
     def test_bulk_write(self) -> None:
         self.coll.insert_one({})