bpo-46479: add typing.reveal_locals

Doc/library/typing.rst

@@ -1963,6 +1963,25 @@ Functions and decorators
 
    .. versionadded:: 3.11
 
+.. function:: reveal_locals()
+
+   Reveal the inferred static types of all local variables.
+
+   When a static type checker encounters a call to this function,
+   it emits a diagnostic with the types of all variables in the current
+   scope. For example::
+
+      def greet(user_id: int) -> None:
+         message = f"Hello user #{user_id}"
+         reveal_locals()  # Revealed local types are: user_id: int, message: str
+
+   Like :func:`reveal_type`, this function is useful for debugging how
+   the type checker understands a piece of code.
+
+   At runtime, this function does nothing.
+
+   .. versionadded:: 3.11
+
 .. decorator:: overload
 
    The ``@overload`` decorator allows describing functions and methods

Lib/test/test_typing.py

@@ -20,7 +20,7 @@
 from typing import get_type_hints
 from typing import get_origin, get_args
 from typing import is_typeddict
-from typing import reveal_type
+from typing import reveal_type, reveal_locals
 from typing import no_type_check, no_type_check_decorator
 from typing import Type
 from typing import NamedTuple, TypedDict
@@ -5290,13 +5290,16 @@ def bar(self):
         self.assertIn('baz', dir(Foo[int]))
 
 
-class RevealTypeTests(BaseTestCase):
+class RevealTests(BaseTestCase):
     def test_reveal_type(self):
         obj = object()
         with captured_stderr() as stderr:
             self.assertIs(obj, reveal_type(obj))
         self.assertEqual(stderr.getvalue(), "Runtime type is 'object'\n")
 
+    def test_reveal_locals(self):
+        self.assertIsNone(reveal_locals())
+
 
 class AllTests(BaseTestCase):
     """Tests for __all__."""

Lib/typing.py

@@ -130,6 +130,7 @@ def _idfunc(_, x):
     'overload',
     'ParamSpecArgs',
     'ParamSpecKwargs',
+    'reveal_locals',
     'reveal_type',
     'runtime_checkable',
     'Text',
@@ -2696,3 +2697,23 @@ def reveal_type(obj: T, /) -> T:
     """
     print(f"Runtime type is {type(obj).__name__!r}", file=sys.stderr)
     return obj
+
+
+def reveal_locals() -> None:
+    """Reveal the inferred static types of all local variables.
+
+    When a static type checker encounters a call to this function,
+    it emits a diagnostic with the types of all variables in the current
+    scope. For example::
+
+        def greet(user_id: int) -> None:
+            message = f"Hello user #{user_id}"
+            reveal_locals()  # Revealed local types are: user_id: int, message: str
+
+    Like :func:`reveal_type`, this function is useful for debugging how
+    the type checker understands a piece of code.
+
+    At runtime, this function does nothing.
+
+    """
+    pass

Misc/NEWS.d/next/Library/2022-01-23-13-21-14.bpo-46479.a-qhRL.rst

@@ -0,0 +1 @@
+Add :func:`typing.reveal_locals`. Patch by Jelle Zijlstra.