Fix import on Python 3.14 and later

newsfragments/160.bugfix.rst

@@ -0,0 +1,2 @@
+Fix importing ``trio_asyncio`` on Python 3.14 and later, where asyncio renamed
+``BaseDefaultEventLoopPolicy``.

tests/test_misc.py

@@ -1,3 +1,4 @@
+import subprocess
 import pytest
 import trio_asyncio
 import asyncio
@@ -8,6 +9,22 @@
     from exceptiongroup import ExceptionGroup, BaseExceptionGroup
 
 
+def test_import_with_private_base_event_loop_policy() -> None:
+    script = """
+import asyncio.events
+
+base_policy = getattr(asyncio.events, "BaseDefaultEventLoopPolicy", None)
+if base_policy is None:
+    base_policy = asyncio.events._BaseDefaultEventLoopPolicy
+else:
+    del asyncio.events.BaseDefaultEventLoopPolicy
+asyncio.events._BaseDefaultEventLoopPolicy = base_policy
+
+import trio_asyncio
+"""
+    subprocess.run([sys.executable, "-c", script], check=True)
+
+
 class Seen:
     flag = 0
 

trio_asyncio/_loop.py

@@ -119,7 +119,15 @@ def _in_trio_context_other_than_sync_loop():
         return False
 
 
-class _TrioPolicy(asyncio.events.BaseDefaultEventLoopPolicy):
+# Python 3.14 renamed this private implementation class with no compatibility
+# alias. Keep supporting older Python versions while accepting the new name.
+try:
+    _BaseDefaultEventLoopPolicy = asyncio.events.BaseDefaultEventLoopPolicy
+except AttributeError:
+    _BaseDefaultEventLoopPolicy = asyncio.events._BaseDefaultEventLoopPolicy
+
+
+class _TrioPolicy(_BaseDefaultEventLoopPolicy):
     @staticmethod
     def _loop_factory():
         raise RuntimeError("Event loop creations shouldn't get here")