gh-103406: Modernize pos-only arguments usage in test_signature (#103407)

Author: sobolevn

Lib/test/test_inspect.py

@@ -3044,14 +3044,9 @@ def foo(a=1, b=2, c=3):
         self.assertEqual(_foo(*ba.args, **ba.kwargs), (12, 10, 20))
 
 
-        def foo(a, b, c, d, **kwargs):
+        def foo(a, b, /, c, d, **kwargs):
             pass
         sig = inspect.signature(foo)
-        params = sig.parameters.copy()
-        params['a'] = params['a'].replace(kind=Parameter.POSITIONAL_ONLY)
-        params['b'] = params['b'].replace(kind=Parameter.POSITIONAL_ONLY)
-        foo.__signature__ = inspect.Signature(params.values())
-        sig = inspect.signature(foo)
         self.assertEqual(str(sig), '(a, b, /, c, d, **kwargs)')
 
         self.assertEqual(self.signature(partial(foo, 1)),
@@ -3556,14 +3551,9 @@ def test_signature_str_positional_only(self):
         P = inspect.Parameter
         S = inspect.Signature
 
-        def test(a_po, *, b, **kwargs):
+        def test(a_po, /, *, b, **kwargs):
             return a_po, kwargs
 
-        sig = inspect.signature(test)
-        new_params = list(sig.parameters.values())
-        new_params[0] = new_params[0].replace(kind=P.POSITIONAL_ONLY)
-        test.__signature__ = sig.replace(parameters=new_params)
-
         self.assertEqual(str(inspect.signature(test)),
                          '(a_po, /, *, b, **kwargs)')
 
@@ -3593,6 +3583,14 @@ def test() -> 42:
         self.assertEqual(sig.return_annotation, 42)
         self.assertEqual(sig, inspect.signature(test))
 
+    def test_signature_replaced(self):
+        def test():
+            pass
+
+        spam_param = inspect.Parameter('spam', inspect.Parameter.POSITIONAL_ONLY)
+        sig = test.__signature__ = inspect.Signature(parameters=(spam_param,))
+        self.assertEqual(sig, inspect.signature(test))
+
     def test_signature_on_mangled_parameters(self):
         class Spam:
             def foo(self, __p1:1=2, *, __p2:2=3):
@@ -4157,16 +4155,9 @@ def test(a, *args, b, z=100, **kwargs):
     def test_signature_bind_positional_only(self):
         P = inspect.Parameter
 
-        def test(a_po, b_po, c_po=3, foo=42, *, bar=50, **kwargs):
+        def test(a_po, b_po, c_po=3, /, foo=42, *, bar=50, **kwargs):
             return a_po, b_po, c_po, foo, bar, kwargs
 
-        sig = inspect.signature(test)
-        new_params = collections.OrderedDict(tuple(sig.parameters.items()))
-        for name in ('a_po', 'b_po', 'c_po'):
-            new_params[name] = new_params[name].replace(kind=P.POSITIONAL_ONLY)
-        new_sig = sig.replace(parameters=new_params.values())
-        test.__signature__ = new_sig
-
         self.assertEqual(self.call(test, 1, 2, 4, 5, bar=6),
                          (1, 2, 4, 5, 6, {}))