gh-107805: Fix signatures of module-level generated functions in `turtle` (#107807)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

3 files changed, 45 insertions, 19 deletions

diff --git a/Lib/test/test_turtle.py b/Lib/test/test_turtle.py
index 3f9f129a3dd..14121a590a5 100644
--- a/Lib/test/test_turtle.py
+++ b/Lib/test/test_turtle.py
@@ -461,5 +461,25 @@ class TestTPen(unittest.TestCase):
             self.assertTrue(tpen.isdown())
 
 
+class TestModuleLevel(unittest.TestCase):
+    def test_all_signatures(self):
+        import inspect
+
+        known_signatures = {
+            'teleport':
+                '(x=None, y=None, *, fill_gap: bool = False) -> None',
+            'undo': '()',
+            'goto': '(x, y=None)',
+            'bgcolor': '(*args)',
+            'pen': '(pen=None, **pendict)',
+        }
+
+        for name in known_signatures:
+            with self.subTest(name=name):
+                obj = getattr(turtle, name)
+                sig = inspect.signature(obj)
+                self.assertEqual(str(sig), known_signatures[name])
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/turtle.py b/Lib/turtle.py
index e542bc95689..6119b7a447e 100644
--- a/Lib/turtle.py
+++ b/Lib/turtle.py
@@ -3920,28 +3920,33 @@ def getmethparlist(ob):
     function definition and the second is suitable for use in function
     call.  The "self" parameter is not included.
     """
-    defText = callText = ""
+    orig_sig = inspect.signature(ob)
     # bit of a hack for methods - turn it into a function
     # but we drop the "self" param.
     # Try and build one for Python defined functions
-    args, varargs, varkw = inspect.getargs(ob.__code__)
-    items2 = args[1:]
-    realArgs = args[1:]
-    defaults = ob.__defaults__ or []
-    defaults = ["=%r" % (value,) for value in defaults]
-    defaults = [""] * (len(realArgs)-len(defaults)) + defaults
-    items1 = [arg + dflt for arg, dflt in zip(realArgs, defaults)]
-    if varargs is not None:
-        items1.append("*" + varargs)
-        items2.append("*" + varargs)
-    if varkw is not None:
-        items1.append("**" + varkw)
-        items2.append("**" + varkw)
-    defText = ", ".join(items1)
-    defText = "(%s)" % defText
-    callText = ", ".join(items2)
-    callText = "(%s)" % callText
-    return defText, callText
+    func_sig = orig_sig.replace(
+        parameters=list(orig_sig.parameters.values())[1:],
+    )
+
+    call_args = []
+    for param in func_sig.parameters.values():
+        match param.kind:
+            case (
+                inspect.Parameter.POSITIONAL_ONLY
+                | inspect.Parameter.POSITIONAL_OR_KEYWORD
+            ):
+                call_args.append(param.name)
+            case inspect.Parameter.VAR_POSITIONAL:
+                call_args.append(f'*{param.name}')
+            case inspect.Parameter.KEYWORD_ONLY:
+                call_args.append(f'{param.name}={param.name}')
+            case inspect.Parameter.VAR_KEYWORD:
+                call_args.append(f'**{param.name}')
+            case _:
+                raise RuntimeError('Unsupported parameter kind', param.kind)
+    call_text = f'({', '.join(call_args)})'
+
+    return str(func_sig), call_text
 
 def _turtle_docrevise(docstr):
     """To reduce docstrings from RawTurtle class for functions
diff --git a/Misc/NEWS.d/next/Library/2023-08-09-13-49-37.gh-issue-107805.ezem0k.rst b/Misc/NEWS.d/next/Library/2023-08-09-13-49-37.gh-issue-107805.ezem0k.rst
new file mode 100644
index 00000000000..263df68f8e5
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-08-09-13-49-37.gh-issue-107805.ezem0k.rst
@@ -0,0 +1 @@
+Fix signatures of module-level generated functions in :mod:`turtle`.