From 775435e5f7297ea0f7685ad5b7bc8c98b5c86dc3 Mon Sep 17 00:00:00 2001
From: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Date: Fri, 9 May 2025 18:42:53 -0700
Subject: [PATCH] gh-132493: Remove __annotations__ usage in
 inspect._signature_is_functionlike (GH-133415)

This check is potentially problematic because it could force evaluation of
annotations unnecessarily. This doesn't trigger for builtin objects (functions,
classes, or modules) with annotations, but it could trigger for third-party objects.

The check was not particularly useful anyway, because it succeeds if ``__annotations__``
is a dict or None, so the only thing this did was guard against objects that have an
``__annotations__`` attribute that is of some other type. That doesn't seem particularly
useful, so I just removed the check.
(cherry picked from commit cb6596c6aa30c8c3213c8746d5590e6e2757a6c1)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
---
 Lib/inspect.py                                |  4 +--
 Lib/test/test_inspect/test_inspect.py         | 31 +++++++++++++++++++
 ...-05-04-17-04-55.gh-issue-132493.huirKi.rst |  2 ++
 3 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-05-04-17-04-55.gh-issue-132493.huirKi.rst

diff --git a/Lib/inspect.py b/Lib/inspect.py
index 52c9bb05b31f37..183e67fabf966e 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -2074,13 +2074,11 @@ def _signature_is_functionlike(obj):
     code = getattr(obj, '__code__', None)
     defaults = getattr(obj, '__defaults__', _void) # Important to use _void ...
     kwdefaults = getattr(obj, '__kwdefaults__', _void) # ... and not None here
-    annotations = getattr(obj, '__annotations__', None)
 
     return (isinstance(code, types.CodeType) and
             isinstance(name, str) and
             (defaults is None or isinstance(defaults, tuple)) and
-            (kwdefaults is None or isinstance(kwdefaults, dict)) and
-            (isinstance(annotations, (dict)) or annotations is None) )
+            (kwdefaults is None or isinstance(kwdefaults, dict)))
 
 
 def _signature_strip_non_python_syntax(signature):
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
index c9b37fcd8f6327..f32395127d3ad0 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -4997,6 +4997,37 @@ def test_signature_annotation_format(self):
                 with self.assertRaisesRegex(NameError, "undefined"):
                     signature_func(ida.f)
 
+    def test_signature_deferred_annotations(self):
+        def f(x: undef):
+            pass
+
+        class C:
+            x: undef
+
+            def __init__(self, x: undef):
+                self.x = x
+
+        sig = inspect.signature(f, annotation_format=Format.FORWARDREF)
+        self.assertEqual(list(sig.parameters), ['x'])
+        sig = inspect.signature(C, annotation_format=Format.FORWARDREF)
+        self.assertEqual(list(sig.parameters), ['x'])
+
+        class CallableWrapper:
+            def __init__(self, func):
+                self.func = func
+                self.__annotate__ = func.__annotate__
+
+            def __call__(self, *args, **kwargs):
+                return self.func(*args, **kwargs)
+
+            @property
+            def __annotations__(self):
+                return self.__annotate__(Format.VALUE)
+
+        cw = CallableWrapper(f)
+        sig = inspect.signature(cw, annotation_format=Format.FORWARDREF)
+        self.assertEqual(list(sig.parameters), ['args', 'kwargs'])
+
     def test_signature_none_annotation(self):
         class funclike:
             # Has to be callable, and have correct
diff --git a/Misc/NEWS.d/next/Library/2025-05-04-17-04-55.gh-issue-132493.huirKi.rst b/Misc/NEWS.d/next/Library/2025-05-04-17-04-55.gh-issue-132493.huirKi.rst
new file mode 100644
index 00000000000000..ad06ee6b7a2757
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-05-04-17-04-55.gh-issue-132493.huirKi.rst
@@ -0,0 +1,2 @@
+Avoid accessing ``__annotations__`` unnecessarily in
+:func:`inspect.signature`.