Request-Reply Pattern with PyZMQ

April 10, 2025

---

This demonstrates a simple request-reply pattern using the PyZMQ package for Python. In the example, the client sends a message to the server which replies back to the client.

Client

The client socket connects to localhost port 5555 to send the message "Hello" to the server. After sending the message to the server, the client waits for the server's reply.

# client.py

import zmq

# Create socket and connect on localhost port 5555
context = zmq.Context()
socket = context.socket(zmq.REQ)
socket.connect("tcp://localhost:5555")

# Send message to server
msg = "Hello"
socket.send_string(msg)
print("Sent:", msg)

# Get reply from server
message = socket.recv_string()
print("Received:", message)

Server

The server socket binds to the localhost on port 5555 (* is localhost). After it receives a message from the client, the server replies with the message "World".

# server.py

import zmq

# Create socket and bind on localhost port 5555
context = zmq.Context()
socket = context.socket(zmq.REP)
socket.bind("tcp://*:5555")
print("Server is running...")

while True:
    # Wait for message from client
    msg = socket.recv_string()
    print("Received:", msg)

    # Send a reply to client
    message = "World"
    socket.send_string(message)
    print("Sent:", message)

Running the example

First, run the server in a terminal session as shown here:

$ uv run server.py
Server is running...

Next, run the client in a different terminal session. The client will quickly receive the reply message from the server.

$ uv run client.py
Sent: Hello
Received: World

After running the client, the server terminal will update with the following:

$ uv run server.py
Server is running...
Received: Hello
Sent: World