[3.14] gh-132493: Remove __annotations__ usage in inspect._signature_is_functionlike (GH-133415) (#133796)

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>

3 files changed, 34 insertions, 3 deletions

diff --git a/Lib/inspect.py b/Lib/inspect.py
index 52c9bb0..183e67f 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 57dc7a2..44f7a54 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -4997,6 +4997,37 @@ class TestSignatureObject(unittest.TestCase):
                 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 0000000..ad06ee6
--- /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`.