typing of Final

examples/five_by_five.py

@@ -1,25 +1,22 @@
 """Simple version of 5x5, developed for/with Textual."""
 
 from pathlib import Path
-from typing import cast
+from typing import TYPE_CHECKING, cast
-import sys
-
-if sys.version_info >= (3, 8):
-    from typing import Final
-else:
-    from typing_extensions import Final
-
-from textual.containers import Horizontal
-from textual.app import App, ComposeResult
-from textual.screen import Screen
-from textual.widget import Widget
-from textual.widgets import Footer, Button, Label
-from textual.css.query import DOMQuery
-from textual.reactive import reactive
-from textual.binding import Binding
 
 from rich.markdown import Markdown
 
+from textual.app import App, ComposeResult
+from textual.binding import Binding
+from textual.containers import Horizontal
+from textual.css.query import DOMQuery
+from textual.reactive import reactive
+from textual.screen import Screen
+from textual.widget import Widget
+from textual.widgets import Button, Footer, Label
+
+if TYPE_CHECKING:
+    from typing import Final
+
 
 class Help(Screen):
     """The help screen for the application."""

src/textual/_typing.py

@@ -19,6 +19,5 @@ __all__ = [
     "Literal",
     "Protocol",
     "runtime_checkable",
-    "TypeAlias",
     "TypedDict",
 ]

src/textual/screen.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import Iterable, Iterator
+from typing import Iterable, Iterator, TYPE_CHECKING
 
 import rich.repr
 from rich.console import RenderableType
@@ -15,11 +15,12 @@ from .dom import DOMNode
 from .timer import Timer
 from ._types import CallbackType
 from .geometry import Offset, Region, Size
-from ._typing import Final
 from .reactive import Reactive
 from .renderables.blank import Blank
 from .widget import Widget
 
+if TYPE_CHECKING:
+    from typing import Final
 
 # Screen updates will be batched so that they don't happen more often than 120 times per second:
 UPDATE_PERIOD: Final[float] = 1 / 120