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docs/examples/guide/structure.py

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+from datetime import datetime
+
+from textual.app import App
+from textual.widget import Widget
+
+
+class Clock(Widget):
+    """A clock app."""
+
+    CSS = """
+    Clock {
+        content-align: center middle;
+    }
+    """
+
+    def on_mount(self):
+        self.set_interval(1, self.refresh)
+
+    def render(self):
+        return datetime.now().strftime("%c")
+
+
+class ClockApp(App):
+    def compose(self):
+        yield Clock()
+
+
+app = ClockApp()
+if __name__ == "__main__":
+    app.run()