gh-82062: Fix support of parameter defaults on methods in extension modules (GH-115270)

Now inspect.signature() supports references to the module globals in
parameter defaults on methods in extension modules.  Previously it was
only supported in functions.  The workaround was to specify the fully
qualified name, including the module name.

4 files changed, 25 insertions, 0 deletions

diff --git a/Lib/inspect.py b/Lib/inspect.py
index d46514f..a0c80bd 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -2285,7 +2285,12 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
 
     module = None
     module_dict = {}
+
     module_name = getattr(obj, '__module__', None)
+    if not module_name:
+        objclass = getattr(obj, '__objclass__', None)
+        module_name = getattr(objclass, '__module__', None)
+
     if module_name:
         module = sys.modules.get(module_name, None)
         if module:
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
index fbef34e..d122403 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -3069,6 +3069,13 @@ class TestSignatureObject(unittest.TestCase):
                 self.assertEqual(inspect.signature(builtin),
                                  inspect.signature(template))
 
+    @unittest.skipIf(MISSING_C_DOCSTRINGS,
+                     "Signature information for builtins requires docstrings")
+    def test_signature_parsing_with_defaults(self):
+        _testcapi = import_helper.import_module("_testcapi")
+        meth = _testcapi.DocStringUnrepresentableSignatureTest.with_default
+        self.assertEqual(str(inspect.signature(meth)), '(self, /, x=1)')
+
     def test_signature_on_non_function(self):
         with self.assertRaisesRegex(TypeError, 'is not a callable object'):
             inspect.signature(42)
diff --git a/Misc/NEWS.d/next/Library/2024-02-11-07-31-43.gh-issue-82062.eeS6w7.rst b/Misc/NEWS.d/next/Library/2024-02-11-07-31-43.gh-issue-82062.eeS6w7.rst
new file mode 100644
index 0000000..a57a591
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-02-11-07-31-43.gh-issue-82062.eeS6w7.rst
@@ -0,0 +1,3 @@
+Fix :func:`inspect.signature()` to correctly handle parameter defaults
+on methods in extension modules that use names defined in the module
+namespace.
diff --git a/Modules/_testcapi/docstring.c b/Modules/_testcapi/docstring.c
index d99fbdd..3f7acba 100644
--- a/Modules/_testcapi/docstring.c
+++ b/Modules/_testcapi/docstring.c
@@ -169,6 +169,13 @@ static PyMethodDef DocStringUnrepresentableSignatureTest_methods[] = {
             "--\n\n"
             "This docstring has a signature with unrepresentable default."
         )},
+    {"with_default",
+        (PyCFunction)test_with_docstring, METH_VARARGS,
+        PyDoc_STR(
+            "with_default($self, /, x=ONE)\n"
+            "--\n\n"
+            "This instance method has a default parameter value from the module scope."
+        )},
     {NULL},
 };
 
@@ -193,5 +200,8 @@ _PyTestCapi_Init_Docstring(PyObject *mod)
     if (PyModule_AddType(mod, &DocStringUnrepresentableSignatureTest) < 0) {
         return -1;
     }
+    if (PyModule_AddObject(mod, "ONE", PyLong_FromLong(1)) < 0) {
+        return -1;
+    }
     return 0;
 }