Revert "pythongh-116110: remove extra processing for the __signature__ attribute"

This reverts commit 1f3c7f3.

Author: skirpichev

Lib/enum.py

@@ -1092,21 +1092,6 @@ def _add_member_(cls, name, member):
         # now add to _member_map_ (even aliases)
         cls._member_map_[name] = member
 
-    @property
-    def __signature__(cls):
-        from inspect import Parameter, Signature
-        if cls._member_names_:
-            return Signature([Parameter('values', Parameter.VAR_POSITIONAL)])
-        else:
-            return Signature([Parameter('new_class_name', Parameter.POSITIONAL_ONLY),
-                              Parameter('names', Parameter.POSITIONAL_OR_KEYWORD),
-                              Parameter('module', Parameter.KEYWORD_ONLY, default=None),
-                              Parameter('qualname', Parameter.KEYWORD_ONLY, default=None),
-                              Parameter('type', Parameter.KEYWORD_ONLY, default=None),
-                              Parameter('start', Parameter.KEYWORD_ONLY, default=1),
-                              Parameter('boundary', Parameter.KEYWORD_ONLY, default=None)])
-
-
 EnumMeta = EnumType         # keep EnumMeta name for backwards compatibility
 
 
@@ -1150,6 +1135,13 @@ class Enum(metaclass=EnumType):
     attributes -- see the documentation for details.
     """
 
+    @classmethod
+    def __signature__(cls):
+        if cls._member_names_:
+            return '(*values)'
+        else:
+            return '(new_class_name, /, names, *, module=None, qualname=None, type=None, start=1, boundary=None)'
+
     def __new__(cls, value):
         # all enum instances are actually created during class construction
         # without calling this method; this method is called by the metaclass'

Lib/inspect.py

@@ -2528,10 +2528,18 @@ def _signature_from_callable(obj, *,
         pass
     else:
         if sig is not None:
+            # since __text_signature__ is not writable on classes, __signature__
+            # may contain text (or be a callable that returns text);
+            # if so, convert it
+            o_sig = sig
+            if not isinstance(sig, (Signature, str)) and callable(sig):
+                sig = sig()
+            if isinstance(sig, str):
+                sig = _signature_fromstr(sigcls, obj, sig)
             if not isinstance(sig, Signature):
                 raise TypeError(
                     'unexpected object {!r} in __signature__ '
-                    'attribute'.format(sig))
+                    'attribute'.format(o_sig))
             return sig
 
     try:

Lib/test/test_inspect/test_inspect.py

@@ -4894,6 +4894,38 @@ def foo(): pass
                 self.assertEqual(signature_func(foo), inspect.Signature())
         self.assertEqual(inspect.get_annotations(foo), {})
 
+    def test_signature_as_str(self):
+        self.maxDiff = None
+        class S:
+            __signature__ = '(a, b=2)'
+
+        self.assertEqual(self.signature(S),
+                         ((('a', ..., ..., 'positional_or_keyword'),
+                           ('b', 2, ..., 'positional_or_keyword')),
+                          ...))
+
+    def test_signature_as_callable(self):
+        # __signature__ should be either a staticmethod or a bound classmethod
+        class S:
+            @classmethod
+            def __signature__(cls):
+                return '(a, b=2)'
+
+        self.assertEqual(self.signature(S),
+                         ((('a', ..., ..., 'positional_or_keyword'),
+                           ('b', 2, ..., 'positional_or_keyword')),
+                          ...))
+
+        class S:
+            @staticmethod
+            def __signature__():
+                return '(a, b=2)'
+
+        self.assertEqual(self.signature(S),
+                         ((('a', ..., ..., 'positional_or_keyword'),
+                           ('b', 2, ..., 'positional_or_keyword')),
+                          ...))
+
     def test_signature_on_derived_classes(self):
         # gh-105080: Make sure that signatures are consistent on derived classes