Streaming & messaging
Kafka-style pub/sub, event consumers, async pipelines, and message-driven workflows.
Dead Letter Queue Failed Messages List Mock in Python
Implements a simple in-memory dead letter queue to collect, list, and retry failed messages, with JSON serialization for inspection in streaming pipelines.
import json
from collections import deque
class Message:
def __init__(self, message_id, payload, attempts=0):
self.message_id = message_id
self.payload = payload
self.attempts = attempts
def __repr__(self):
return f"Message(id={self.message_id}, attempts={self.attempts})"
c…How to Build a Flow Control Credit Window in Python
A Python class that reserves, confirms, releases, and settles credit to limit message flow and prevent overload in streaming pipelines.
class CreditWindow:
def __init__(self, max_credit=1000):
self.max_credit = max_credit
self.used_credit = 0
self.pending_credit = 0
def try_reserve(self, amount):
available = self.max_credit - self.used_credit - self.pending_credit
if available >= amount:
…How to Build a Mock Change Data Capture Event Stream in Python
Generate a deterministic list of mock CDC events with event IDs, stream positions, payloads, and timestamps for testing streaming pipelines.
from itertools import count
from random import choice, randint, seed
from datetime import datetime, timedelta
seed(42) # Make output deterministic
event_types = ["INSERT", "UPDATE", "DELETE"]
table_names = ["users", "orders", "products", "payments"]
counter = count(1)
def mock_cdc_event(stream_index: int) -> dict:
…How to Encode and Decode Avro Data in Python (Roundtrip)
Serialize a Python dict to Avro binary bytes and decode it back using the fastavro-compatible avro library.
import io
import json
from avro.schema import parse
from avro.io import DatumWriter, DatumReader, BinaryEncoder, BinaryDecoder
def avro_roundtrip(schema_json, data):
schema = parse(json.dumps(schema_json))
bytes_writer = io.BytesIO()
encoder = BinaryEncoder(bytes_writer)
writer = DatumWriter(schema)
…How to Implement Publish-Subscribe Fanout with Multiple Subscribers in Python
Create a simple publish-subscribe system in Python that broadcasts messages to multiple subscriber callbacks for a given topic.
import time
class PubSub:
def __init__(self):
self.subscribers = {}
def subscribe(self, topic, callback):
if topic not in self.subscribers:
self.subscribers[topic] = []
self.subscribers[topic].append(callback)
def publish(self, topic, message):
if topic in sel…How to Mock MQTT Topic Subscriptions with QoS in Python
Build a lightweight MQTT client mock that tracks topic subscriptions with QoS levels and simulates wildcard message delivery.
import time
from collections import defaultdict
class MockMQTTClient:
def __init__(self):
self.subscriptions = defaultdict(list)
self.messages = []
def subscribe(self, topic, qos=0):
self.subscriptions[topic].append(qos)
print(f"Subscribed to '{topic}' with QoS {qos}")
…How to Mock a Kafka Producer Batch Send in Python
Simulate a Kafka producer in Python that sends batched JSON events with mock partitions and latency for testing streaming pipelines without a real broker.
import json
import random
import time
from datetime import datetime
class MockKafkaProducer:
def __init__(self, topic):
self.topic = topic
self.sent_messages = []
def send(self, value, key=None):
message = {
"topic": self.topic,
"key": key,
"value"…How to deduplicate messages by ID in Python
Track seen message IDs in a set to skip duplicate messages and store unique content in a dict, with exact output showing which messages were added or skipped.
import time
class MessageStore:
def __init__(self):
self.seen_ids = set()
self.messages = {}
def add(self, message_id, content, timestamp=None):
timestamp = timestamp or time.time()
if message_id in self.seen_ids:
return False
self.seen_ids.add(message_…How to mock RabbitMQ queue binding with routing keys in Python
A mock demonstration of binding a queue to an exchange with multiple routing keys in RabbitMQ using Python and pika, without a real broker connection.
import pika
import sys
def bind_queue_with_routing(channel, queue_name, exchange_name, routing_keys):
"""
Mock RabbitMQ queue binding with routing keys.
Prints the binding configuration instead of connecting to a real broker.
"""
for routing_key in routing_keys:
binding = {
"q…Mock Watermark Late Event Side Output in Python
Simulates watermarking in a streaming pipeline by classifying events as on-time or late using timestamps and delays.
from datetime import datetime, timedelta
from typing import List, Tuple
def watermark_mock(
events: List[Tuple[datetime, str]], watermark_delay: timedelta, max_delay: timedelta
) -> Tuple[List[Tuple[datetime, str]], List[Tuple[datetime, str]]]:
"""Simulate watermarking: events arriving on time vs. late by ch…Using the retained message flag in MQTT with Python
This script subscribes to an MQTT topic and prints the retained flag for each received message, demonstrating how to distinguish retained messages from normal ones.
import paho.mqtt.client as mqtt
def on_connect(client, userdata, flags, rc):
print(f"Connected with result code {rc}")
# Subscribe to a topic and check retained flag
client.subscribe("test/retained")
print("Subscribed to test/retained")
def on_message(client, userdata, msg):
# msg.retain is the M…Browse by section
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Streaming & messaging — Python code examples
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