From 920076096f697e3542312b7c7896e9a6892480d7 Mon Sep 17 00:00:00 2001
From: Julien Danjou <julien@danjou.info>
Date: Wed, 5 Aug 2026 23:15:29 +0200
Subject: [PATCH] fix: read the tornado global live instead of an import-time
 snapshot

#679 replaced `if tornado:` with a `_HAS_TORNADO` bool computed once at
import, to stop `truthy-bool` flagging the module object as always true.
But only one of the two call sites was converted: the `retry()` decorator
still dereferences the live `tornado` global right after testing the
snapshot. The two desync as soon as anything reassigns the global.

A/B verified against a2af454: `tenacity.tornado = None` followed by any
`@tenacity.retry` decoration returned normally before, and now raises
`AttributeError: 'NoneType' object has no attribute 'gen'`. Nulling the
module global is the standard way a downstream suite exercises the
non-tornado path without uninstalling tornado.

Replace the constant with a `_has_tornado()` function so both call sites
read the live global and cannot drift apart. As a bonus this needs no
`redundant-expr` suppression: the check reads as a plain return rather than
the left operand of an `and`.

Change-Id: I6f0fbb9cad3d4e46599b0cae1b5b60378742fd1f
---
 ...ix-tornado-global-desync-8c2d40fa71b9e35a.yaml |  7 +++++++
 tenacity/__init__.py                              | 15 +++++++++------
 tests/test_tornado.py                             | 13 +++++++++++++
 3 files changed, 29 insertions(+), 6 deletions(-)
 create mode 100644 releasenotes/notes/fix-tornado-global-desync-8c2d40fa71b9e35a.yaml

diff --git a/releasenotes/notes/fix-tornado-global-desync-8c2d40fa71b9e35a.yaml b/releasenotes/notes/fix-tornado-global-desync-8c2d40fa71b9e35a.yaml
new file mode 100644
index 00000000..c5a19e53
--- /dev/null
+++ b/releasenotes/notes/fix-tornado-global-desync-8c2d40fa71b9e35a.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Setting ``tenacity.tornado = None`` -- the usual way a downstream test
+    suite forces the non-tornado code path -- raised ``AttributeError: 'NoneType'
+    object has no attribute 'gen'`` from the ``@retry`` decorator. Tornado
+    availability is read live again rather than from an import-time snapshot.
diff --git a/tenacity/__init__.py b/tenacity/__init__.py
index 51925efa..530b63a5 100644
--- a/tenacity/__init__.py
+++ b/tenacity/__init__.py
@@ -89,10 +89,13 @@
 except ImportError:
     tornado = None  # type: ignore[assignment]
 
-# mypy resolves `tornado` to the module (it only ever sees the `try` branch),
-# so testing the module object for truthiness reads as an always-true check.
-# Keep the availability answer in a plain bool instead.
-_HAS_TORNADO = tornado is not None
+
+def _has_tornado() -> bool:
+    # A function, not a module-level constant: test suites force the
+    # non-tornado path by setting `tenacity.tornado = None`, so the answer has
+    # to be computed from the live global every time it is asked for.
+    return tornado is not None
+
 
 if t.TYPE_CHECKING:
     if sys.version_info >= (3, 11):
@@ -786,7 +789,7 @@ def wrap(f: t.Callable[P, R]) -> _RetryDecorated[P, R]:
         ):
             r = AsyncRetrying(*dargs, **dkw)
         elif (
-            _HAS_TORNADO
+            _has_tornado()
             and hasattr(tornado.gen, "is_coroutine_function")
             and tornado.gen.is_coroutine_function(f)
         ):
@@ -801,7 +804,7 @@ def wrap(f: t.Callable[P, R]) -> _RetryDecorated[P, R]:
 
 from tenacity.asyncio import AsyncRetrying  # noqa: E402
 
-if _HAS_TORNADO:
+if _has_tornado():
     from tenacity.tornadoweb import TornadoRetrying
 
 
diff --git a/tests/test_tornado.py b/tests/test_tornado.py
index 9233cca3..f20a41b4 100644
--- a/tests/test_tornado.py
+++ b/tests/test_tornado.py
@@ -15,9 +15,11 @@
 import unittest
 from collections.abc import Generator
 from typing import Any
+from unittest import mock
 
 from tornado import gen, testing
 
+import tenacity
 from tenacity import RetryError, retry, stop_after_attempt, tornadoweb
 
 from .test_tenacity import NoIOErrorAfterCount
@@ -73,6 +75,17 @@ def retryable(thing: NoIOErrorAfterCount) -> None:
         finally:
             gen.is_coroutine_function = old_attr
 
+    def test_tornado_set_to_none(self) -> None:
+        # Forcing the non-tornado path by nulling the module global is how
+        # downstream suites exercise installs without tornado.
+        with mock.patch.object(tenacity, "tornado", None):
+
+            @retry(stop=stop_after_attempt(1))
+            def retryable() -> int:
+                return 1
+
+            assert retryable() == 1
+
 
 if __name__ == "__main__":
     unittest.main()