[Python] How to reconnect zeromq client to server?

I have just started using the Python ZeroMQ library, pyzmq==27.1.0.

I am running on a Raspberry Pi 5 (debian 12 - bookworm)

I want to make sure my client reconnects if my server stops and restarts. When I run the server first it works fine. But if I run the client first or the server stops and restarts then the client doesn't connect.

I was hoping it might automatically re-connect, but that doesn't work for me. I keep trying to send and keep getting

Operation cannot be accomplished in current state
​

even when the server restarts.

import time
import zmq

class Test:
def __init__(self):
context = zmq.Context()
self._socket = context.socket(zmq.REQ)

# Suggested settings for auto-reconnect
self._socket.setsockopt(zmq.LINGER, 0)
self._socket.setsockopt(zmq.RECONNECT_IVL, 1000)
self._socket.setsockopt(zmq.RECONNECT_IVL_MAX, 5000)

self._socket.connect(f"tcp://localhost:5555")

def request(self, request: str) -> str:
try:
self._socket.send(request.encode())

# Get the reply.
if self._socket.poll(1000, zmq.POLLIN):
message = self._socket.recv()
else:
raise Exception("Machine control service is not responding")
return message.decode()
except Exception as ex:
print("ERROR", ex)


def run():
control = Test()

while True:
reply = control.request("READALL")
print("Received reply:", reply)
time.sleep(1)


if __name__ == "__main__":
run()


I tried disconnecting and re-connecting, but even while the server is down the client appears to connect successfully but cannot send. Then when the server comes up again, it continues to fail to send.

def __init__(self):
self._connection_string = f"tcp://localhost:{SERVER_PORT}"
context = zmq.Context()
self._socket = context.socket(zmq.REQ)
self._socket_connected = False
self._gpio_input_states = ""

def _connect(self):
if not self._socket_connected:
print("connect")
self._socket.connect(self._connection_string)
self._socket_connected = True
print("connected!!!!!")

def _disconnect(self):
if self._socket_connected:
print("disconnect")
self._socket.disconnect(self._connection_string)
self._socket_connected = False

def request(self, request: str) -> str:
try:
self._connect()
self._socket.send(request.encode())

# Get the reply.
if self._socket.poll(1000, zmq.POLLIN):
message = self._socket.recv()
else:
raise Exception("Machine control service is not responding")
return message.decode()
except Exception as ex:
self._disconnect()
raise MachineControlInterfaceException(f"Failed to send request to machine control service. Reason: {ex}")


Should it be possible to do this? What am I doing wrong?

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