Add NoArcadeWindowError and have_window function

* Add NoArcadeWindowError subclassing RuntimeError

* Make arcade.window_commands.get_window() raise NoArcadeWindowError when no window exists

* Add arcade.window_commands.have_window() function

* Improve documentation of get_window() function

Author: pushfoo

arcade/exceptions.py

@@ -7,6 +7,7 @@
 from typing import TypeVar
 
 __all__ = [
+    "NoArcadeWindowError",
     "OutsideRangeError",
     "IntOutsideRangeError",
     "FloatOutsideRangeError",
@@ -23,6 +24,15 @@
 _CT = TypeVar("_CT")  # Comparable type, ie supports the <= operator
 
 
+
+class NoArcadeWindowError(RuntimeError):
+    """No valid Arcade window exists.
+    
+    It may be handled as a :py:class:`RuntimeError`.
+    """
+    ...
+ 
+
 class OutsideRangeError(ValueError):
     """
     Raised when a value is outside and expected range

arcade/window_commands.py

@@ -15,6 +15,7 @@
 import pyglet
 
 from arcade.types import RGBA255, Color
+from arcade.exceptions import NoArcadeWindowError
 
 if TYPE_CHECKING:
     from arcade import Window
@@ -25,6 +26,7 @@
 __all__ = [
     "get_display_size",
     "get_window",
+    "have_window",
     "set_window",
     "close_window",
     "run",
@@ -54,14 +56,31 @@ def get_display_size(screen_id: int = 0) -> tuple[int, int]:
     return screen.width, screen.height
 
 
-def get_window() -> Window:
+def have_window() -> bool:
+    """Returns ``True`` if an Arcade window exists.
+    
+    .. tip:: Use this to avoid an :py:class:`~arcade.exceptions.NoArcadeWindowError`.
+    
+
+    Returns:
+        Whether a :py:class:`~arcade.Window` exists.
     """
-    Return a handle to the current window.
+    return _window is None
 
-    :return: Handle to the current window.
+
+def get_window() -> Window:
+    """Return a handle to the current window.
+    
+    If no window exists, it will raise an exception you can
+    handle as a :py:class:`RuntimeError`. Use :py:func:`have_window`
+    to prevent raising an exception.
+
+    Raises:
+        :py:class:`~arcade.exceptions.NoArcadeWindowError` when no window exists.
     """
+    # This avoids calling the function above because it may be a hot code path.
     if _window is None:
-        raise RuntimeError("No window is active. It has not been created yet, or it was closed.")
+        raise NoArcadeWindowError("No window is active. It has not been created yet, or it was closed.")
 
     return _window