gh-108901: Add inspect.Signature.from_frame

Doc/library/inspect.rst

@@ -817,6 +817,19 @@ 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>`.
+
+ Notice that it is impossible to get signatures
+ with defaults or annotations from frames,
+ because annotations are stored
+ in a function inside ``__defaults__``, ``__kwdefaults__``,
+ and ``__annotations__`` attributes.
+
+ .. versionadded:: 3.13
+
 
 .. class:: Parameter(name, kind, *, default=Parameter.empty, annotation=Parameter.empty)
 

Doc/whatsnew/3.13.rst

@@ -361,6 +361,11 @@ and only logged in :ref:`Python Development Mode <devmode>` or on :ref:`Python
 built on debug mode <debug-build>`.
 (Contributed by Victor Stinner in :gh:`62948`.)
 
+inspect
+-------
+
+* Add :meth:`inspect.Signature.from_frame` to get signatures from frame objects.
+
 ipaddress
 ---------
 

Lib/inspect.py

@@ -2419,16 +2419,34 @@ 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 +3111,29 @@ 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.
+
+ Notice that it is impossible to get signatures
+ with defaults or annotations from frames,
+ because annotations are stored
+ in a function inside ``__defaults__``, ``__kwdefaults__``,
+ and ``__annotations__`` attributes.
+ """
+ if not isframe(frame):
+ raise TypeError(f'Frame object expected, got:{type(frame)}')
+
+ return _signature_from_code(
+ frame.f_code,
+ annotations={},
+ defaults=(),
+ kwdefaults={},
+ cls=cls,
+ is_duck_function=False,
+ )
+
  @property
  def parameters(self):
  return self._parameters

Lib/test/test_inspect/test_inspect.py

@@ -4623,6 +4623,104 @@ class D2(D1):
  self.assertEqual(inspect.signature(D2), inspect.signature(D1))
 
 
+class TestSignatureFromFrame(unittest.TestCase):
+ def test_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, /, b, *e, c, d, **f)')
+
+ def test_from_frame_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, /, b, *e, c, d, **f)')
+
+ def test_from_frame_no_locals(self):
+ ns ={}
+ def inner():
+ ns['fr'] = inspect.currentframe()
+
+ inner()
+ self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+ '()')
+
+ def test_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, b, **c)')
+
+ def test_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, /, b, *c)')
+
+ def test_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, /, b, *c)')
+
+ def test_clear_frame(self):
+ ns ={}
+ def inner(a=1, /, c=5, *, b=2):
+ ns['fr'] = inspect.currentframe()
+
+ inner()
+ ns['fr'].clear()
+ self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+ '(a, /, c, *, b)')
+
+ def test_from_method_frame(self):
+ ns ={}
+ class _A:
+ def inner(self, a, *, b):
+ ns['fr'] = inspect.currentframe()
+
+ _A().inner(1, b=2)
+ self.assertEqual(str(inspect.Signature.from_frame(ns['fr'])),
+ '(self, a, *, b)')
+
+ def test_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, /, c, *, b)')
+
+ def test_from_frame_mod(self):
+ self.assertEqual(str(inspect.Signature.from_frame(mod.fr)),
+ '(x, y)')
+ self.assertEqual(str(inspect.Signature.from_frame(mod.fr.f_back)),
+ '(a, /, b, c, d, e, f, *g, **h)')
+
+ def test_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 +1,2 @@
+Add :meth:`inspect.Signature.from_frame` to get a signature
+from a frame object.