gh-107155: Fix help() for lambda function with return annotation (GH-107401)

2 files changed, 28 insertions, 2 deletions

diff --git a/Lib/pydoc.py b/Lib/pydoc.py
index 6d145ab..9bb64fe 100755
--- a/Lib/pydoc.py
+++ b/Lib/pydoc.py
@@ -1144,7 +1144,8 @@ class HTMLDoc(Doc):
                 # XXX lambda's won't usually have func_annotations['return']
                 # since the syntax doesn't support but it is possible.
                 # So removing parentheses isn't truly safe.
-                argspec = argspec[1:-1] # remove parentheses
+                if not object.__annotations__:
+                    argspec = argspec[1:-1] # remove parentheses
         if not argspec:
             argspec = '(...)'
 
@@ -1586,7 +1587,8 @@ location listed above.
                 # XXX lambda's won't usually have func_annotations['return']
                 # since the syntax doesn't support but it is possible.
                 # So removing parentheses isn't truly safe.
-                argspec = argspec[1:-1] # remove parentheses
+                if not object.__annotations__:
+                    argspec = argspec[1:-1]
         if not argspec:
             argspec = '(...)'
         decl = asyncqualifier + title + argspec + note
diff --git a/Lib/test/test_pydoc/test_pydoc.py b/Lib/test/test_pydoc/test_pydoc.py
index 0dd24e6..d7a333a 100644
--- a/Lib/test/test_pydoc/test_pydoc.py
+++ b/Lib/test/test_pydoc/test_pydoc.py
@@ -693,6 +693,30 @@ class PydocDocTest(unittest.TestCase):
         finally:
             pydoc.getpager = getpager_old
 
+    def test_lambda_with_return_annotation(self):
+        func = lambda a, b, c: 1
+        func.__annotations__ = {"return": int}
+        with captured_output('stdout') as help_io:
+            pydoc.help(func)
+        helptext = help_io.getvalue()
+        self.assertIn("lambda (a, b, c) -> int", helptext)
+
+    def test_lambda_without_return_annotation(self):
+        func = lambda a, b, c: 1
+        func.__annotations__ = {"a": int, "b": int, "c": int}
+        with captured_output('stdout') as help_io:
+            pydoc.help(func)
+        helptext = help_io.getvalue()
+        self.assertIn("lambda (a: int, b: int, c: int)", helptext)
+
+    def test_lambda_with_return_and_params_annotation(self):
+        func = lambda a, b, c: 1
+        func.__annotations__ = {"a": int, "b": int, "c": int, "return": int}
+        with captured_output('stdout') as help_io:
+            pydoc.help(func)
+        helptext = help_io.getvalue()
+        self.assertIn("lambda (a: int, b: int, c: int) -> int", helptext)
+
     def test_namedtuple_fields(self):
         Person = namedtuple('Person', ['nickname', 'firstname'])
         with captured_stdout() as help_io: