PYTHON-4781 Handle errors on Async PyMongo import (#1873)

(cherry picked from commit e03f8f2)

Author: blink1073

pymongo/__init__.py

@@ -88,7 +88,6 @@
 
 from pymongo import _csot
 from pymongo._version import __version__, get_version_string, version_tuple
-from pymongo.asynchronous.mongo_client import AsyncMongoClient
 from pymongo.common import MAX_SUPPORTED_WIRE_VERSION, MIN_SUPPORTED_WIRE_VERSION
 from pymongo.cursor import CursorType
 from pymongo.operations import (
@@ -105,6 +104,14 @@
 from pymongo.synchronous.mongo_client import MongoClient
 from pymongo.write_concern import WriteConcern
 
+try:
+    from pymongo.asynchronous.mongo_client import AsyncMongoClient
+except Exception as e:
+    # PYTHON-4781: Importing asyncio can fail on Windows.
+    import warnings as _warnings
+
+    _warnings.warn(f"Failed to import Async PyMongo: {e!r}", ImportWarning, stacklevel=2)
+
 version = __version__
 """Current version of PyMongo."""