pythongh-108901: Add inspect.Signature.from_frame

Doc/library/inspect.rst

@@ -817,6 +817,13 @@ function.
        .. versionchanged:: 3.10
          The *globals*, *locals*, and *eval_str* parameters were added.
 
+   .. classmethod:: Signature.from_frame(frame)
+
+       Return a :class:`Signature` (or its subclass) object for a given
+       :ref:`frame object <frame-objects>`.
+
+       .. versionadded:: 3.13
+
 
 .. class:: Parameter(name, kind, *, default=Parameter.empty, annotation=Parameter.empty)
 

Lib/inspect.py

@@ -2419,16 +2419,29 @@ def _signature_from_function(cls, func, skip_bound_arg=True,
     Parameter = cls._parameter_cls
 
     # Parameter information.
-    func_code = func.__code__
+    annotations = get_annotations(func, globals=globals, locals=locals, eval_str=eval_str)
+    return _signature_from_code(
+        func.__code__,
+        annotations=annotations,
+        defaults=func.__defaults__,
+        kwdefaults=func.__kwdefaults__,
+        cls=cls,
+        is_duck_function=is_duck_function,
+    )
+
+
+def _signature_from_code(
+    func_code,
+    *,
+    annotations, defaults, kwdefaults,
+    cls, is_duck_function,
+):
     pos_count = func_code.co_argcount
     arg_names = func_code.co_varnames
     posonly_count = func_code.co_posonlyargcount
     positional = arg_names[:pos_count]
     keyword_only_count = func_code.co_kwonlyargcount
     keyword_only = arg_names[pos_count:pos_count + keyword_only_count]
-    annotations = get_annotations(func, globals=globals, locals=locals, eval_str=eval_str)
-    defaults = func.__defaults__
-    kwdefaults = func.__kwdefaults__
 
     if defaults:
         pos_default_count = len(defaults)
@@ -3093,6 +3106,37 @@ def from_callable(cls, obj, *,
                                         follow_wrapper_chains=follow_wrapped,
                                         globals=globals, locals=locals, eval_str=eval_str)
 
+    @classmethod
+    def from_frame(cls, frame):
+        """Constructs Signature from a given frame object."""
+        if not isframe(frame):
+            raise TypeError(f'Frame object expected, got: {type(frame)}')
+
+        func_code = frame.f_code
+        pos_count = func_code.co_argcount
+        arg_names = func_code.co_varnames
+        keyword_only_count = func_code.co_kwonlyargcount
+
+        defaults = []
+        kwdefaults = {}
+        if frame.f_locals:
+            for name in arg_names[:pos_count]:
+                if name in frame.f_locals:
+                    defaults.append(frame.f_locals[name])
+
+            for name in arg_names[pos_count : pos_count + keyword_only_count]:
+                if name in frame.f_locals:
+                    kwdefaults.update({name: frame.f_locals[name]})
+
+        return _signature_from_code(
+            func_code,
+            annotations={},
+            defaults=defaults,
+            kwdefaults=kwdefaults,
+            cls=cls,
+            is_duck_function=False,
+        )
+
     @property
     def parameters(self):
         return self._parameters

Lib/test/test_inspect/test_inspect.py

@@ -4623,6 +4623,96 @@ class D2(D1):
         self.assertEqual(inspect.signature(D2), inspect.signature(D1))
 
 
+class TestSignatureFromFrame(unittest.TestCase):
+    def test_signature_from_frame(self):
+        ns = {}
+        def inner(a, /, b, *e, c: int = 3, d, **f) -> None:
+            ns['fr'] = inspect.currentframe()
+
+        inner(1, 2, d=4)
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '(a=1, /, b=2, *e, c=3, d=4, **f)')
+
+    def test_signature_with_pos_only_defaults(self):
+        ns = {}
+        def inner(a=1, /, b=2, *e, c: int = 3, d, **f) -> None:
+            ns['fr'] = inspect.currentframe()
+
+        inner(d=4)
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '(a=1, /, b=2, *e, c=3, d=4, **f)')
+
+    def test_signature_from_frame_no_locals(self):
+        ns = {}
+        def inner():
+            ns['fr'] = inspect.currentframe()
+
+        inner()
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '()')
+
+    def test_signature_from_frame_no_pos(self):
+        ns = {}
+        def inner(*, a, b=2, **c):
+            ns['fr'] = inspect.currentframe()
+
+        inner(a=1)
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '(*, a=1, b=2, **c)')
+
+    def test_signature_from_frame_no_kw(self):
+        ns = {}
+        def inner(a, /, b, *c):
+            ns['fr'] = inspect.currentframe()
+
+        inner(1, 2)
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '(a=1, /, b=2, *c)')
+
+    def test_signature_from_frame_with_nonlocal(self):
+        fr = None
+        def inner(a, /, b, *c):
+            nonlocal fr
+            fr = inspect.currentframe()
+
+        inner(1, 2)
+        self.assertEqual(str(inspect.Signature.from_frame(fr)),
+                         '(a=1, /, b=2, *c)')
+
+    def test_signature_from_method_frame(self):
+        ns = {}
+        class _A:
+            def inner(self, a, *, b):
+                ns['fr'] = inspect.currentframe()
+            def __repr__(self):
+                return '_A'
+
+        _A().inner(1, b=2)
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '(self=_A, a=1, *, b=2)')
+
+    def test_signature_from_frame_defaults_change(self):
+        ns = {}
+        def inner(a=1, /, c=5, *, b=2):
+            a = 3
+            ns['fr'] = inspect.currentframe()
+            b = 4
+
+        inner()
+        self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+                         '(a=3, /, c=5, *, b=4)')
+
+    def test_signature_from_frame_mod(self):
+        self.assertEqual(str(inspect.Signature.from_frame(mod.fr)),
+                         '(x=11, y=14)')
+        self.assertEqual(str(inspect.Signature.from_frame(mod.fr.f_back)),
+                         '(a=7, /, b=8, c=9, d=3, e=4, f=5, *g, **h)')
+
+    def test_signature_from_not_frame(self):
+        with self.assertRaisesRegex(TypeError, 'Frame object expected'):
+            inspect.Signature.from_frame(lambda: ...)
+
+
 class TestParameterObject(unittest.TestCase):
     def test_signature_parameter_kinds(self):
         P = inspect.Parameter

Misc/NEWS.d/next/Library/2024-03-09-12-55-44.gh-issue-108901.s9VClL.rst

@@ -0,0 +1,3 @@
+Add :meth:`inspect.Signature.from_frame` to get a singature from a frame
+object, it will be used as a new alternative for older
+:func:`inspect.getargvalues` and :func:`inspect.formatargvalues`.