PYTHON-3084 MongoClient/Database/Collection should not implement Iterable (#909)

Author: ShaneHarvey

pymongo/collection.py

@@ -3146,8 +3146,8 @@ def find_one_and_update(
             **kwargs,
         )
 
-    def __iter__(self) -> "Collection[_DocumentType]":
-        return self
+    # See PYTHON-3084.
+    __iter__ = None
 
     def __next__(self) -> NoReturn:
         raise TypeError("'Collection' object is not iterable")

pymongo/database.py

@@ -1009,8 +1009,8 @@ def validate_collection(
 
         return result
 
-    def __iter__(self) -> "Database[_DocumentType]":
-        return self
+    # See PYTHON-3084.
+    __iter__ = None
 
     def __next__(self) -> NoReturn:
         raise TypeError("'Database' object is not iterable")

pymongo/mongo_client.py

@@ -1973,8 +1973,8 @@ def __enter__(self) -> "MongoClient[_DocumentType]":
     def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
         self.close()
 
-    def __iter__(self) -> "MongoClient[_DocumentType]":
-        return self
+    # See PYTHON-3084.
+    __iter__ = None
 
     def __next__(self) -> NoReturn:
         raise TypeError("'MongoClient' object is not iterable")

test/test_client.py

@@ -26,7 +26,7 @@
 import sys
 import threading
 import time
-from typing import Type, no_type_check
+from typing import Iterable, Type, no_type_check
 
 sys.path[0:0] = [""]
 
@@ -210,10 +210,26 @@ def test_getattr(self):
         self.assertIn("has no attribute '_does_not_exist'", str(context.exception))
 
     def test_iteration(self):
-        def iterate():
-            [a for a in self.client]
-
-        self.assertRaises(TypeError, iterate)
+        client = self.client
+        if "PyPy" in sys.version:
+            msg = "'NoneType' object is not callable"
+        else:
+            msg = "'MongoClient' object is not iterable"
+        # Iteration fails
+        with self.assertRaisesRegex(TypeError, msg):
+            for _ in client:  # type: ignore[misc] # error: "None" not callable  [misc]
+                break
+        # Index fails
+        with self.assertRaises(TypeError):
+            _ = client[0]
+        # next fails
+        with self.assertRaisesRegex(TypeError, "'MongoClient' object is not iterable"):
+            _ = next(client)
+        # .next() fails
+        with self.assertRaisesRegex(TypeError, "'MongoClient' object is not iterable"):
+            _ = client.next()
+        # Do not implement typing.Iterable.
+        self.assertNotIsInstance(client, Iterable)
 
     def test_get_default_database(self):
         c = rs_or_single_client(

test/test_collection.py

@@ -21,7 +21,7 @@
 import sys
 from codecs import utf_8_decode  # type: ignore
 from collections import defaultdict
-from typing import no_type_check
+from typing import Iterable, no_type_check
 
 from pymongo.database import Database
 
@@ -124,7 +124,26 @@ def test_getattr(self):
         self.assertEqual(coll2.write_concern, coll4.write_concern)
 
     def test_iteration(self):
-        self.assertRaises(TypeError, next, self.db)
+        coll = self.db.coll
+        if "PyPy" in sys.version:
+            msg = "'NoneType' object is not callable"
+        else:
+            msg = "'Collection' object is not iterable"
+        # Iteration fails
+        with self.assertRaisesRegex(TypeError, msg):
+            for _ in coll:  # type: ignore[misc] # error: "None" not callable  [misc]
+                break
+        # Non-string indices will start failing in PyMongo 5.
+        self.assertEqual(coll[0].name, "coll.0")
+        self.assertEqual(coll[{}].name, "coll.{}")
+        # next fails
+        with self.assertRaisesRegex(TypeError, "'Collection' object is not iterable"):
+            _ = next(coll)
+        # .next() fails
+        with self.assertRaisesRegex(TypeError, "'Collection' object is not iterable"):
+            _ = coll.next()
+        # Do not implement typing.Iterable.
+        self.assertNotIsInstance(coll, Iterable)
 
 
 class TestCollection(IntegrationTest):

test/test_database.py

@@ -16,7 +16,7 @@
 
 import re
 import sys
-from typing import Any, List, Mapping
+from typing import Any, Iterable, List, Mapping
 
 sys.path[0:0] = [""]
 
@@ -94,7 +94,26 @@ def test_getattr(self):
         self.assertIn("has no attribute '_does_not_exist'", str(context.exception))
 
     def test_iteration(self):
-        self.assertRaises(TypeError, next, self.client.pymongo_test)
+        db = self.client.pymongo_test
+        if "PyPy" in sys.version:
+            msg = "'NoneType' object is not callable"
+        else:
+            msg = "'Database' object is not iterable"
+        # Iteration fails
+        with self.assertRaisesRegex(TypeError, msg):
+            for _ in db:  # type: ignore[misc] # error: "None" not callable  [misc]
+                break
+        # Index fails
+        with self.assertRaises(TypeError):
+            _ = db[0]
+        # next fails
+        with self.assertRaisesRegex(TypeError, "'Database' object is not iterable"):
+            _ = next(db)
+        # .next() fails
+        with self.assertRaisesRegex(TypeError, "'Database' object is not iterable"):
+            _ = db.next()
+        # Do not implement typing.Iterable.
+        self.assertNotIsInstance(db, Iterable)
 
 
 class TestDatabase(IntegrationTest):