pythongh-107155: Fix help(lambda_func) when lambda_func has __annotations__ with return key.

Author: Eclips4

Lib/pydoc.py

@@ -1500,10 +1500,9 @@ def docroutine(self, object, name=None, mod=None, cl=None):
                 argspec = str(signature)
                 if realname == '<lambda>':
                     title = self.bold(name) + ' lambda '
-                    # 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
+                    # Since lambda's cannot have a parenthesis in their signature,
+                    # it's safe to replace them.
+                    argspec = argspec.replace("(", "").replace(")", "")
         if not argspec:
             argspec = '(...)'
         decl = asyncqualifier + title + argspec + note

Lib/test/test_pydoc.py

@@ -684,6 +684,14 @@ def test_help_output_redirect(self):
         finally:
             pydoc.getpager = getpager_old
 
+    def test_lambda_with_annotations(self):
+        func = lambda a, b, c: 1
+        func.__annotations__ = {"return": int}
+        with captured_stdout() as help_io:
+            pydoc.help(func)
+        helptext = help_io.getvalue()
+        self.assertIn("lambda a, b, c -> int", helptext)
+
     def test_namedtuple_fields(self):
         Person = namedtuple('Person', ['nickname', 'firstname'])
         with captured_stdout() as help_io: