implement TYPE_CHECKING using __type_checking__

methane · methane · commit 406718c81d71 · 2025-03-25T09:45:12.000+09:00
diff --git a/Lib/typing.py b/Lib/typing.py
@@ -3409,7 +3409,7 @@ def __ror__(self, other):
 
 
 # Constant that's True when type checking, but False here.
-TYPE_CHECKING = False
+TYPE_CHECKING = __type_checking__
 
 
 class IO(Generic[AnyStr]):
