PYTHON-3193 - Add ResourceWarning for unclosed MongoClients in __del__

doc/changelog.rst

@@ -42,6 +42,16 @@ PyMongo 4.9 brings a number of improvements including:
 - Fixed a bug where PyMongo would raise ``InvalidBSON: date value out of range``
   when using :attr:`~bson.codec_options.DatetimeConversion.DATETIME_CLAMP` or
   :attr:`~bson.codec_options.DatetimeConversion.DATETIME_AUTO` with a non-UTC timezone.
+- Added a warning to unclosed MongoClient instances
+  telling users to explicitly close clients when finished with them to avoid leaking resources.
+  Here's an example of what the warning looks like:
+
+  .. code-block::
+
+    sys:1: ResourceWarning: Unclosed MongoClient opened at:
+        File "/Users/<user>/my_file.py", line 8, in <module>``
+            client = MongoClient()
+    Call MongoClient.close() to safely shut down your client and free up resources.
 
 Issues Resolved
 ...............

pymongo/asynchronous/mongo_client.py

@@ -34,6 +34,7 @@
 
 import contextlib
 import os
+import warnings
 import weakref
 from collections import defaultdict
 from typing import (
@@ -864,6 +865,7 @@ def __init__(
         )
 
         self._opened = False
+        self._closed = False
         self._init_background()
 
         if _IS_SYNC and connect:
@@ -1173,6 +1175,22 @@ def __getitem__(self, name: str) -> database.AsyncDatabase[_DocumentType]:
         """
         return database.AsyncDatabase(self, name)
 
+    def __del__(self) -> None:
+        """Check that this AsyncMongoClient has been closed and issue a warning if not."""
+        try:
+            if not self._closed:
+                warnings.warn(
+                    (
+                        f"Unclosed {type(self).__name__} opened at:\n{self._topology_settings._stack}"
+                        f"Call {type(self).__name__}.close() to safely shut down your client and free up resources."
+                    ),
+                    ResourceWarning,
+                    stacklevel=2,
+                    source=self,
+                )
+        except AttributeError:
+            pass
+
     def _close_cursor_soon(
         self,
         cursor_id: int,
@@ -1540,6 +1558,7 @@ async def close(self) -> None:
         if self._encrypter:
             # TODO: PYTHON-1921 Encrypted MongoClients cannot be re-opened.
             await self._encrypter.close()
+        self._closed = True
 
     if not _IS_SYNC:
         # Add support for contextlib.aclosing.

pymongo/asynchronous/settings.py

@@ -82,7 +82,7 @@ def __init__(
         self._topology_id = ObjectId()
         # Store the allocation traceback to catch unclosed clients in the
         # test suite.
-        self._stack = "".join(traceback.format_stack())
+        self._stack = "".join(traceback.format_stack()[:-2])
 
     @property
     def seeds(self) -> Collection[tuple[str, int]]:

pymongo/synchronous/mongo_client.py

@@ -34,6 +34,7 @@
 
 import contextlib
 import os
+import warnings
 import weakref
 from collections import defaultdict
 from typing import (
@@ -863,6 +864,7 @@ def __init__(
         )
 
         self._opened = False
+        self._closed = False
         self._init_background()
 
         if _IS_SYNC and connect:
@@ -1172,6 +1174,22 @@ def __getitem__(self, name: str) -> database.Database[_DocumentType]:
         """
         return database.Database(self, name)
 
+    def __del__(self) -> None:
+        """Check that this MongoClient has been closed and issue a warning if not."""
+        try:
+            if not self._closed:
+                warnings.warn(
+                    (
+                        f"Unclosed {type(self).__name__} opened at:\n{self._topology_settings._stack}"
+                        f"Call {type(self).__name__}.close() to safely shut down your client and free up resources."
+                    ),
+                    ResourceWarning,
+                    stacklevel=2,
+                    source=self,
+                )
+        except AttributeError:
+            pass
+
     def _close_cursor_soon(
         self,
         cursor_id: int,
@@ -1535,6 +1553,7 @@ def close(self) -> None:
         if self._encrypter:
             # TODO: PYTHON-1921 Encrypted MongoClients cannot be re-opened.
             self._encrypter.close()
+        self._closed = True
 
     if not _IS_SYNC:
         # Add support for contextlib.closing.

pymongo/synchronous/settings.py

@@ -82,7 +82,7 @@ def __init__(
         self._topology_id = ObjectId()
         # Store the allocation traceback to catch unclosed clients in the
         # test suite.
-        self._stack = "".join(traceback.format_stack())
+        self._stack = "".join(traceback.format_stack()[:-2])
 
     @property
     def seeds(self) -> Collection[tuple[str, int]]:

pyproject.toml

@@ -95,6 +95,9 @@ filterwarnings = [
     "module:please use dns.resolver.Resolver.resolve:DeprecationWarning",
     # https://github.com/dateutil/dateutil/issues/1314
     "module:datetime.datetime.utc:DeprecationWarning:dateutil",
+    # TODO: Remove both of these in https://jira.mongodb.org/browse/PYTHON-4731
+    "ignore:Unclosed AsyncMongoClient*",
+    "ignore:Unclosed MongoClient*",
 ]
 markers = [
     "auth_aws: tests that rely on pymongo-auth-aws",