ch15: typing.cast example

15-more-types/cast/tcp_echo.py

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+import asyncio
+
+from asyncio import StreamReader, StreamWriter
+from asyncio.trsock import TransportSocket
+from typing import cast
+
+async def handle_echo(reader: StreamReader, writer: StreamWriter) -> None:
+    data = await reader.read(100)
+    message = data.decode()
+    addr = writer.get_extra_info('peername')
+
+    print(f"Received {message!r} from {addr!r}")
+
+    print(f"Send: {message!r}")
+    writer.write(data)
+    await writer.drain()
+
+    print("Close the connection")
+    writer.close()
+
+async def main() -> None:
+    server = await asyncio.start_server(
+        handle_echo, '127.0.0.1', 8888)
+
+    # tag::CAST[]
+    socket_list = cast(tuple[TransportSocket, ...], server.sockets)
+    addr = socket_list[0].getsockname()
+    # end::CAST[]
+    print(f'Serving on {addr}')
+
+    async with server:
+        await server.serve_forever()
+
+asyncio.run(main())

15-more-types/cast/tcp_echo_no_cast.py

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+import asyncio
+
+from asyncio import StreamReader, StreamWriter
+
+async def handle_echo(reader: StreamReader, writer: StreamWriter) -> None:
+    data = await reader.read(100)
+    message = data.decode()
+    addr = writer.get_extra_info('peername')
+
+    print(f"Received {message!r} from {addr!r}")
+
+    print(f"Send: {message!r}")
+    writer.write(data)
+    await writer.drain()
+
+    print("Close the connection")
+    writer.close()
+
+async def main() -> None:
+    server = await asyncio.start_server(
+        handle_echo, '127.0.0.1', 8888)
+
+    addr = server.sockets[0].getsockname()
+    print(f'Serving on {addr}')
+
+    async with server:
+        await server.serve_forever()
+
+asyncio.run(main())