chore: import upstream snapshot with attribution

docs/md/how_to/python/virtual_server/polars.md

@@ -0,0 +1,49 @@
+# Polars Virtual Server
+
+Perspective provides a built-in virtual server for
+[Polars](https://pola.rs/), allowing `<perspective-viewer>` clients to query
+in-memory Polars DataFrames over WebSocket.
+
+## Installation
+
+```bash
+pip install perspective-python polars
+```
+
+## Usage
+
+Create a server that exposes Polars DataFrames to browser clients:
+
+```python
+import polars as pl
+import tornado.web
+import tornado.ioloop
+from perspective.virtual_servers.polars import PolarsVirtualServer
+from perspective.handlers.tornado import PerspectiveTornadoHandler
+
+# Load data into Polars DataFrames
+df = pl.read_parquet("data.parquet")
+
+# Create virtual server backed by Polars (dict of name -> DataFrame)
+server = PolarsVirtualServer({"my_table": df})
+
+# Serve over WebSocket
+app = tornado.web.Application([
+    (r"/websocket", PerspectiveTornadoHandler, {"perspective_server": server}),
+])
+
+app.listen(8080)
+tornado.ioloop.IOLoop.current().start()
+```
+
+Connect from the browser:
+
+```javascript
+const websocket = await perspective.websocket("ws://localhost:8080/websocket");
+const table = await websocket.open_table("my_table");
+document.getElementById("viewer").load(table);
+```
+
+## Examples
+
+- [Python Polars example](https://github.com/perspective-dev/perspective/tree/master/examples/python-polars-virtual)