So here's the basic code (sorry it's long)
import argparse import asyncio from contextvars import ContextVar import sys # This thing is the offender message_var = ContextVar("message") class ServerProtocol(asyncio.Protocol): def connection_made(self, transport): peername = transport.get_extra_info("peername") print("Server: Connection from {}".format(peername)) self.transport = transport def data_received(self, data): message = data.decode() print("Server: Data received: {!r}".format(message)) print("Server: Send: {!r}".format(message)) self.transport.write(data) print("Server: Close the client socket") self.transport.close() class ClientProtocol(asyncio.Protocol): def __init__(self, on_conn_lost): self.on_conn_lost = on_conn_lost self.transport = None self.is_connected: bool = False def connection_made(self, transport): self.transport = transport self.is_connected = True def data_received(self, data): # reading back supposed contextvar message = message_var.get() print(f"{message} : {data.decode()}") def connection_lost(self, exc): print("The server closed the connection") self.is_connected = False self.on_conn_lost.set_result(True) def send(self, message: str): # Setting context var message_var.set(message) if self.transport: self.transport.write(message.encode()) def close(self): self.transport.close() self.is_connected = False if not self.on_conn_lost.done(): self.on_conn_lost.set_result(True) async def get_input(client: ClientProtocol): loop = asyncio.get_running_loop() while client.is_connected: message = await loop.run_in_executor(None, input, ">>>") if message == "q": client.close() return client.send(message) async def main(args): host = "127.0.0.1" port = 5001 loop = asyncio.get_running_loop() if args.server: server = await loop.create_server(lambda: ServerProtocol(), host, port) async with server: await server.serve_forever() return on_conn_lost = loop.create_future() client = ClientProtocol(on_conn_lost) await loop.create_connection(lambda: client, host, port) await get_input(client) if __name__ == "__main__": parser = argparse.ArgumentParser() parser.add_argument( "--server", "-s", default=False, action="store_true", help="Start server" ) arguments = parser.parse_args(sys.argv[1:]) asyncio.run(main(args=arguments)) This crashes with the following exception:
Exception in callback _ProactorReadPipeTransport._loop_reading(<_OverlappedF...shed result=4>) handle: <Handle _ProactorReadPipeTransport._loop_reading(<_OverlappedF...shed result=4>)> Traceback (most recent call last): File "C:\Users\brent\AppData\Local\Programs\Python\Python310\lib\asyncio\events.py", line 80, in _run self._context.run(self._callback, *self._args) File "C:\Users\brent\AppData\Local\Programs\Python\Python310\lib\asyncio\proactor_events.py", line 320, in _loop_reading self._data_received(data, length) File "C:\Users\brent\AppData\Local\Programs\Python\Python310\lib\asyncio\proactor_events.py", line 270, in _data_received self._protocol.data_received(data) File "E:\Development\Python\ibcs2023\_prep\experimental\asyncio_context.py", line 40, in data_received message = message_var.get() LookupError: <ContextVar name='message' at 0x0000023F30A54FE0> The server closed the connection Why does calling message = message_var.get() cause a crash? Why can't Python find the context var? Why is data_received not in the same context as send? How can I keep them in the same context?
I'm working on a larger project with the main branch of Textual and it uses a contextvar that loses context every time a message is received using a modified version of the code above.
