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How to Calculate VPC Subnet CIDR Details in Python
Compute network address, broadcast address, address count, prefix length, and netmask for any IPv4 CIDR using the Python standard library's ipaddress module.
import ipaddress
def subnet_details(cidr: str) -> dict:
network = ipaddress.ip_network(cidr, strict=False)
return {
"network_address": str(network.network_address),
"broadcast_address": str(network.broadcast_address),
"num_addresses": network.num_addresses,
"prefix_length": ne…How to Mock ELB Target Health Status in Python
Simulate AWS Elastic Load Balancer target health checks with a Python dict that mutates status and healthy host counts.
from random import randint
def elb_target_mock_status(target_id, healthy=True):
targets = {
1: {"Id": "i-001", "Status": "healthy", "Port": 80, "HealthyHostCount": 1},
2: {"Id": "i-002", "Status": "unhealthy", "Port": 80, "HealthyHostCount": 0},
3: {"Id": "i-003", "Status": "healthy", "Por…How to Mock a Fast uv pip sync in Python
Simulate a fast uv pip sync by mocking file operations and subprocess calls to test dependency installation workflows.
import os
import shutil
import subprocess
import sys
import tempfile
from pathlib import Path
def uv_pip_sync_fast_install_mock(requirements_text: str) -> dict:
"""Simulate a fast uv pip sync by mocking file operations and subprocess calls."""
mock_dir = Path(tempfile.mkdtemp(prefix="uv_mock_"))
req_lines…pytest mark slow skip integration
Uses pytest markers to select fast tests, skip unfinished ones, and run integration checks with verbose output.
import pytest
def test_fast():
assert 1 + 1 == 2
@pytest.mark.slow
def test_slow():
import time
time.sleep(1)
assert 5 * 5 == 25
@pytest.mark.skip(reason="Not ready for production")
def test_skipped():
assert 2 + 2 == 5
@pytest.mark.integration
def test_integration():
database = {"users": […How to Use uvloop Faster Event Loop
Install uvloop at startup to replace asyncio's default event loop with a faster libuv-based one, with a graceful fallback when it's unavailable.
import asyncio
try:
import uvloop
uvloop.install()
USING_UVLOOP = True
except ImportError:
USING_UVLOOP = False
async def fetch_data(index):
await asyncio.sleep(0.01)
return f"data-{index}"
async def main():
tasks = [fetch_data(i) for i in range(10)]
results = await asyncio.gather(*…How to Write a Fast Smoke Test for a Critical Path in Python
A quick smoke test that validates the /health critical path executes fast enough, raising errors on wrong paths or slow responses.
import time
def smoke_test(path):
if path != "/health":
raise ValueError("Critical path expected /health")
start = time.perf_counter()
# Simulate the critical health check work
time.sleep(0.01)
elapsed = time.perf_counter() - start
if elapsed > 0.05:
raise RuntimeError("Health …How to mock the domain center in an onion architecture in Python
Define a repository interface and an in-memory mock to test domain services without touching infrastructure.
from abc import ABC, abstractmethod
from dataclasses import dataclass
from typing import Dict, List, Optional
@dataclass
class Order:
id: int
customer: str
items: List[str]
total: float
class OrderRepository(ABC):
@abstractmethod
def find_by_id(self, order_id: int) -> Optional[Order]:
…Dedupe processed message IDs in Python
Filters an inbox of messages by removing items whose IDs have already been processed, using a set for fast lookups.
from pathlib import Path
import json
def dedupe_processed_ids(inbox_file: Path, processed_file: Path) -> list:
processed = set(json.loads(processed_file.read_text()))
inbox = json.loads(inbox_file.read_text())
deduped = [item for item in inbox if item["id"] not in processed]
return deduped
if __nam…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 Implement an In-Memory Pub/Sub System in Python
This code implements a simple in-memory publish/subscribe system in Python, allowing topics, callbacks, and message broadcasting.
class PubSub:
def __init__(self):
self.topics = {}
def subscribe(self, topic, callback):
if topic not in self.topics:
self.topics[topic] = []
self.topics[topic].append(callback)
return lambda: self.unsubscribe(topic, callback)
def unsubscribe(self, topic, callb…How to Deduplicate Messages in Python by ID
This code consumes a mock inbox of JSON messages and deduplicates them by message ID, keeping either the first or last occurrence.
import json
from collections import OrderedDict
mock_inbox = [
{"id": 1, "message": "hello", "timestamp": "2024-01-01T10:00:00Z"},
{"id": 2, "message": "world", "timestamp": "2024-01-01T10:01:00Z"},
{"id": 1, "message": "hello", "timestamp": "2024-01-01T10:00:00Z"},
{"id": 3, "message": "test", "times…Implementing Fallback with Cached Stale Data in Python
This code demonstrates a resilient data-fetching pattern that caches successful responses, falls back to cached data when the external API fails, and returns stale data as a last-resort fallback.
import random
import time
# Simulated cache dictionary: key -> (value, timestamp)
_cache = {}
_CACHE_TTL = 3 # seconds
# Mock data source (simulates an unreliable external API)
def fetch_mock_data(key):
failure = random.random() < 0.4 # 40% chance of failure
if failure:
raise ConnectionError("Mock …How to Mock a Server-Side Load Balancer in Python
A simple Python class that mimics a server-side load balancer with round-robin, random, and least-connections selection strategies.
import itertools
import random
class LoadBalancer:
def __init__(self, servers=None):
self.servers = servers if servers else ["server1", "server2", "server3"]
self.counter = itertools.count(1)
def round_robin(self):
return next(self.counter) % len(self.servers)
def random_selectio…How to Broadcast a Small Lookup Table in Python
Simulates broadcasting a small lookup table by iterating key-value pairs and emitting packed rows to subscribers with deterministic output.
import random
# Generate a deterministic mock broadcast of a small lookup table
# with 5 keys and random integer values (seeded for reproducibility)
data = {
"sensor_a": 22,
"sensor_b": 87,
"sensor_c": 43,
"sensor_d": 65,
"sensor_e": 31,
}
# Simulate a broadcast to subscribers by iterating and p…How to Use Broadcast Variables as Read-Only in PySpark (Mock Example)
Share a lookup dict across Spark executors with a broadcast variable and verify its read-only behavior in a local mock.
from pyspark import SparkContext, SparkConf
def main():
conf = SparkConf().setAppName("BroadcastMock").setMaster("local[2]")
sc = SparkContext(conf=conf)
lookup = {"a": 1, "b": 2, "c": 3}
broadcast_lookup = sc.broadcast(lookup)
data = ["a", "b", "c", "a", "unknown"]
rdd = sc.parallel…Modeling a Hive Metastore Table Schema in Python
A dataclass that mimics a Hive metastore table schema—columns, partition keys, storage format, and location—with helper methods for description and mutation.
from dataclasses import dataclass, field
from typing import Dict, List, Optional
@dataclass
class HiveTable:
"""Simple mock of a Hive metastore table schema."""
name: str
database: str = "default"
columns: List[Dict[str, str]] = field(default_factory=list)
partition_keys: List[Dict[str, str]] = f…How to Mock a Feature Store Online Lookup in Python
This code simulates an online feature store with single and batch retrieval methods, using a dict-backed cache and timestamps.
import random
import time
class OnlineFeatureStore:
def __init__(self):
self.features = {}
def put(self, entity_id: str, feature_name: str, value):
key = (entity_id, feature_name)
self.features[key] = (value, time.time())
def get(self, entity_id: str, feature_name: str):
…Broadcast a Small Reference Table in Python
Simulates SQL-style broadcasting of a small lookup table against a larger fact table in memory for mockups or load tests.
import random
def broadcast_mock(target, source, columns):
result = {}
for col in columns:
if col in target and col in source:
result[col] = target[col] + [source[col][i % len(source[col])] for i in range(len(target[col]))]
elif col in target:
result[col] = target[col]
…How to Mock Sticky Session Read-Your-Writes in Python
Simulates a sticky session store that routes reads for a session to the node where the last write occurred, demonstrating read-your-writes consistency.
class StickySessionStore:
def __init__(self):
self.data = {}
self.session_nodes = {}
def write(self, session_id, key, value):
self.data[key] = value
self.session_nodes[session_id] = key
return f"Wrote {key}={value} for session {session_id}"
def read(self, session_i…How to Speed Up Column Lookups with DataFrame Index in Python
Use pandas set_index to make repeated column value lookups O(1)-style fast instead of scanning the whole DataFrame each time.
import pandas as pd
# Mock dataset with duplicate customer IDs
data = {"customer_id": [101, 102, 103, 101, 104, 102],
"order_amount": [250.0, 85.5, 300.0, 175.25, 420.0, 95.75]}
df = pd.DataFrame(data)
df = df.set_index("customer_id")
# Simulated lookup request
search_id = 102
# Fast index-based lookup (no…How to Mock a TLS Certificate Rotation Schedule in Python
Simulate a TLS certificate rotation schedule with a Python class that tracks last and next rotation dates and decides when to rotate.
import datetime
import random
import time
class CertRotator:
def __init__(self, cert_name, rotation_days=30):
self.cert_name = cert_name
self.rotation_days = rotation_days
self.last_rotated = datetime.date.today() - datetime.timedelta(days=random.randint(10, 25))
self.next_rotatio…How to Mock Terraform Plan and Apply in Python
This code provides a lightweight Python mock of Terraform's plan and apply commands, helping you simulate infrastructure changes without real cloud resources.
class MockTerraform:
def __init__(self):
self.plans = [
{"id": 1, "action": "create", "resource": "aws_instance.web"},
{"id": 2, "action": "update", "resource": "aws_s3_bucket.data"},
{"id": 3, "action": "destroy", "resource": "aws_iam_user.legacy"}
]
sel…How to Mock a Slow Startup Probe for Fast Testing in Python
This code shows how to replace a slow startup probe's initialization with a mock to make tests run fast and reliably.
import time
from unittest.mock import Mock, patch
class StartupProbe:
def __init__(self, init_time):
self.init_time = init_time
self.ready = False
def initialize(self):
time.sleep(self.init_time)
self.ready = True
return self.ready
def run_startup_probe(probe):
…How to Mock an Ingress TLS Certificate Manager in Python
Build a mock TLS certificate manager for ingress that issues, checks, and renews certificates with expiry tracking — useful for testing deployment workflows before touching real infrastructure.
import ssl
import socket
from datetime import datetime, timedelta
class TLSCertManager:
def __init__(self, hostname):
self.hostname = hostname
self.certificates = {}
def request_certificate(self, domain, days_valid=90):
"""Mock a certificate issuance request that stores a cert with e…Browse by section
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