gh-132493: Remove __annotations__ usage in inspect._signature_is_func…

…tionlike 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.
python · JelleZijlstra · May 10, 2025 · May 5, 2025 · May 5, 2025 · May 9, 2025
commit 22dbf9fab874e8b5d5cae540d182c575af5d4835
diff --git 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
@@ -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.keys()), ['x'])
+        sig = inspect.signature(C, annotation_format=Format.FORWARDREF)
+        self.assertEqual(list(sig.parameters.keys()), ['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.keys()), ['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
@@ -0,0 +1,2 @@
+Avoid accessing ``__annotations__`` unnecessarily in
+:func:`inspect.signature`.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Avoid accessing ``__annotations__`` unnecessarily in
		:func:`inspect.signature`.