Streaming & messaging
Kafka-style pub/sub, event consumers, async pipelines, and message-driven workflows.
How to Aggregate Periodic Snapshot Data in Python
Generates mock snapshot data and groups values into periods to compute average aggregates with Python's standard library.
import random
from collections import defaultdict
def snapshot_aggregate(n=10, period=3):
data = defaultdict(list)
for i in range(n):
key = f"item_{i % period}"
data[key].append(random.randint(1, 100))
return dict(data)
def aggregate_periodic(snapshots, period=3):
result = {}
for …How to Implement Backpressure Pause Producer with a Bounded Queue in Python
Places a Producer thread that sends items into a bounded queue with backpressure: on Full, it pauses to let the consumer catch up.
import threading
import time
import queue
import random
class Producer:
def __init__(self, q):
self.q = q
self.running = True
def produce(self):
while self.running:
item = random.randint(1, 100)
try:
self.q.put(item, timeout=0.5)
…How to Partition and Order Kafka-Style Messages by Key in Python
Group messages with the same key into ordered buckets using hashing and a defaultdict, mimicking Kafka partition ordering.
from dataclasses import dataclass
from collections import defaultdict
@dataclass
class Message:
key: str
content: str
def partition_and_order(messages, num_partitions=3):
partitions = defaultdict(list)
for msg in messages:
partition_id = hash(msg.key) % num_partitions
partitions[parti…How to Simulate a Micro-Batch Interval Trigger in Python
A dataclass-based mock that emits batch numbers at fixed intervals, mimicking a micro-batch streaming scheduler for testing and development.
import time
from dataclasses import dataclass, field
from typing import List, Callable
@dataclass
class MicroBatchTriggerMock:
batch_interval_seconds: float = 0.5
max_batches: int = 5
_batches_emitted: int = 0
_next_emit_time: float = field(init=False, default=0)
def start(self, on_batch: Callab…How to Track Session Windows with Gap Timeout in Python
A Python class that groups events into sessions, closing a session when the gap between events exceeds a timeout threshold.
import time
class SessionWindow:
"""Track sessions with a gap timeout (mock)."""
def __init__(self, timeout_seconds=5):
self.timeout = timeout_seconds
self.session_start = None
self.last_event_time = None
self.event_count = 0
self.events = []
def add_event…How to Wrap Message Attributes in a CloudEvent with Python
Create a minimal CloudEvent dataclass that wraps arbitrary message attributes into a JSON envelope, matching CloudEvents 1.0 spec.
import json
from dataclasses import dataclass, field, asdict
from typing import Any, Dict
from datetime import datetime, timezone
@dataclass
class CloudEvent:
message_attributes: Dict[str, Any] = field(default_factory=dict)
def wrap(self, event_id: str, source: str, event_type: str, data: Any):
self…How to mock a CQRS projector read model update in Python
Build a CQRS projector class that maintains denormalized read models by applying domain events in a mock order-processing service.
from dataclasses import dataclass, field
from typing import Dict, List, Optional
@dataclass
class OrderReadModel:
order_id: str
customer_name: str
total: float
status: str = "pending"
items: List[Dict] = field(default_factory=list)
def apply_event(self, event_type: str, payload: Dict) -> Non…Mock Kafka Consumer Group Partition Assignment in Python
Simulates a Kafka consumer group's round-robin partition assignment with a Python class and prints assignments per consumer.
from collections import defaultdict
class ConsumerGroupAssignment:
def __init__(self, group_name, topics_partitions):
self.group_name = group_name
self.consumers = {}
self.assignments = defaultdict(set)
topics_partitions = sorted(
[(topic, partition) for topic, partiti…Mock Protobuf Binary Encoding in Python
Demonstrates a minimal protobuf-like binary encoding and decoding of an event dataclass using varints and length-delimited fields in pure Python.
import struct
from dataclasses import dataclass
@dataclass
class Event:
id: int
user_id: int
action: str
def encode(self) -> bytes:
# Mock protobuf-like binary encoding using varint and length-delimited fields
buf = bytearray()
# field 1: varint id (tag = (1 << 3) | 0 = 8)
…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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