more general app

sandbox/basic.py

@@ -91,7 +91,7 @@ class Success(Widget):
         return Text("This is a success message", justify="center")
 
 
-class BasicApp(App):
+class BasicApp(App, css_path="basic.css"):
     """A basic app demonstrating CSS"""
 
     def on_load(self):
@@ -158,7 +158,7 @@ class BasicApp(App):
         tweet_body.refresh(layout=True)
 
 
-app = BasicApp(css_path="basic.css")
+app = BasicApp()
 
 if __name__ == "__main__":
     app.run()

sandbox/nest.py

@@ -16,7 +16,7 @@ class TextWidget(Widget):
         return TEXT
 
 
-class AutoApp(App):
+class AutoApp(App, css_path="nest.css"):
     def on_mount(self) -> None:
         self.bind("t", "tree")
 
@@ -30,9 +30,3 @@ class AutoApp(App):
 
     def action_tree(self):
         self.log(self.screen.tree)
-
-
-app = AutoApp(css_path="nest.css")
-
-if __name__ == "__main__":
-    app.run()

src/textual/app.py

@@ -109,6 +109,8 @@ class App(Generic[ReturnType], DOMNode):
 
     """
 
+    CSS_PATH: str | None = None
+
     def __init__(
         self,
         driver_class: Type[Driver] | None = None,
@@ -188,8 +190,7 @@ class App(Generic[ReturnType], DOMNode):
 
         self.stylesheet = Stylesheet(variables=self.get_css_variables())
         self._require_styles_update = False
-
+        self.css_path = css_path or self.CSS_PATH
-        self.css_path = css_path
 
         self.registry: set[MessagePump] = set()
         self.devtools = DevtoolsClient()
@@ -203,6 +204,10 @@ class App(Generic[ReturnType], DOMNode):
 
         super().__init__()
 
+    def __init_subclass__(cls, css_path: str | None = None) -> None:
+        super().__init_subclass__()
+        cls.CSS_PATH = css_path
+
     title: Reactive[str] = Reactive("Textual")
     sub_title: Reactive[str] = Reactive("")
     background: Reactive[str] = Reactive("black")

src/textual/cli/cli.py

@@ -47,7 +47,6 @@ def import_app(import_name: str) -> App:
     from textual.app import App
 
     lib, _colon, name = import_name.partition(":")
-    name = name or "app"
 
     if lib.endswith(".py"):
         # We're assuming the user wants to load a .py file
@@ -60,10 +59,41 @@ def import_app(import_name: str) -> App:
         global_vars: dict[str, object] = {}
         exec(py_code, global_vars)
 
-        try:
+        if name:
-            app = global_vars[name]
+            # User has give a name, use that
-        except KeyError:
+            try:
-            raise AppFail(f"App {name!r} not found in {lib!r}")
+                app = global_vars[name]
+            except KeyError:
+                raise AppFail(f"App {name!r} not found in {lib!r}")
+        else:
+            # User has not given a name
+            if "app" in global_vars:
+                # App exists, lets use that
+                try:
+                    app = global_vars[name]
+                except KeyError:
+                    raise AppFail(f"App {name!r} not found in {lib!r}")
+            else:
+                # Find a App class or instance that is *not* the base class
+                apps = [
+                    value
+                    for key, value in global_vars.items()
+                    if (
+                        isinstance(value, App)
+                        or (inspect.isclass(value) and issubclass(value, App))
+                        and value is not App
+                    )
+                ]
+                if not apps:
+                    raise AppFail(
+                        f'Unable to find app in {lib!r}, try specifying app with "foo.py:app"'
+                    )
+                if len(apps) > 1:
+                    raise AppFail(
+                        f'Multiple apps found {lib!r}, try specifying app with "foo.py:app"'
+                    )
+                app = apps[0]
+
     else:
         # Assuming the user wants to import the file
         sys.path.append("")
@@ -78,7 +108,7 @@ def import_app(import_name: str) -> App:
             raise AppFail(f"Unable to find {name!r} in {module!r}")
 
     if inspect.isclass(app) and issubclass(app, App):
-        app = App()
+        app = app()
 
     return cast(App, app)