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How to Implement RBAC Permission Checks with a Route Decorator in Python
Build a reusable Python decorator that checks a user's role against allowed roles and raises a custom PermissionError when access is denied.
from functools import wraps
from enum import Enum
class Role(Enum):
ADMIN = "admin"
MODERATOR = "moderator"
USER = "user"
class PermissionError(Exception):
pass
def require_role(*allowed_roles):
def decorator(func):
@wraps(func)
def wrapper(user_role, *args, **kwargs):
…How to Mock a Webhook Subscribe Callback URL in Python
Mock a webhook subscribe callback URL using Python's http.server to receive and parse POST requests sent by webhook providers.
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
class WebhookHandler(BaseHTTPRequestHandler):
def do_POST(self):
content_length = int(self.headers.get('Content-Length', 0))
payload = json.loads(self.rfile.read(content_length)) if content_length else {}
print…How to Mock an API Key Header Authentication Server in Python
A minimal HTTP server that validates requests using an X-API-Key header and returns JSON responses for authenticated and unauthenticated calls.
import json
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
API_KEYS = {"test-user": "secret-key-123"}
class AuthHandler(BaseHTTPRequestHandler):
def do_GET(self):
auth = self.headers.get("X-API-Key")
if not auth or auth not in API_KEYS.values():
self.send_response…How to Prefix Python API URIs with a Version Slug
Build a versioned API endpoint by optionally adding a version prefix like v1 to the URL path using the stdlib urllib module.
from urllib.parse import urlparse
BASE_URL = "https://api.example.com"
def build_uri(resource, version="v1"):
"""Mock a versioned API URI with an optional v1 prefix."""
parsed = urlparse(BASE_URL)
prefix = f"/{version}" if version else ""
return f"{parsed.scheme}://{parsed.netloc}{prefix}/{resource.l…How to Propagate X-Request-ID in Python
Generate a unique request ID when one is missing and pass it through API calls for distributed tracing.
import uuid
def generate_request_id() -> str:
"""Generate a unique request ID similar to X-Request-ID header."""
return str(uuid.uuid4())
def propagate_request_id(request_id: str | None) -> str:
"""Return the request ID for propagation, generating one if missing."""
if request_id:
return re…How to Validate Data in Python for Beginners
A beginner-friendly Python class for validating required fields, types, ranges, and allowed choices in dict payloads.
import json
from typing import Any, Dict, List, Optional, Union
class Validator:
"""A simple validate data helper designed for beginners."""
def __init__(self, data: Union[Dict[str, Any], List[Any]]):
self.data = data
self.errors: Dict[str, str] = {}
def validate_required(self, field: s…How to Validate Request Body JSON Against a Schema in Python
Build a lightweight schema validator to check required fields, types, string lengths, allowed values, and nested objects in a JSON request body.
import json
def validate_against_schema(data, schema, path=""):
errors = []
if not isinstance(data, dict):
errors.append(f"{path}: expected object, got {type(data).__name__}")
return errors
for field, rules in schema.items():
field_path = f"{path}.{field}" if path else field
…Sort Python list by query param order_by
Sort a list of dataclass objects dynamically by a field name passed as a query param, with asc/desc direction support.
from dataclasses import dataclass
@dataclass
class Item:
name: str
price: int
def sort_items(items, order_by, direction="asc"):
if order_by not in ("name", "price"):
raise ValueError(f"Unsupported sort field: {order_by}")
reverse = direction.lower() == "desc"
return sorted(items, key=l…At Most Once Fire-and-Forget Mock in Python
A Python mock that enforces send() is called at most once and records the arguments for verification.
class FireForgetMock:
def __init__(self):
self._calls = 0
self._last_args = None
self._last_kwargs = None
def send(self, *args, **kwargs):
if self._calls > 0:
raise RuntimeError("send() called more than once")
self._calls += 1
self._last_args = args
…How to Build a Materialized View Updater Consumer Mock in Python
A mock consumer that queues change events and triggers refresh callbacks to simulate materialized view updates.
import time
from collections import deque
from dataclasses import dataclass, field
from typing import Callable, Deque, Optional
@dataclass
class MaterializedViewUpdater:
"""Mock updater that consumes change events and refreshes a view."""
refresh: Optional[Callable[[str], None]] = None
queue: Deque[tuple…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 a Tumbling Window Counter in Python
Count events that fall within a fixed-size sliding time window using a deque and pruning logic.
from collections import deque
import time
class TumblingWindowCounter:
def __init__(self, window_size_seconds):
self.window_size = window_size_seconds
self.window = deque()
def add_event(self, timestamp):
self.window.append(timestamp)
def count(self, current_time):
while…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 Mock a Kafka Rebalance Listener in Python
Simulate Kafka consumer rebalance callbacks (on_partitions_revoked and on_partitions_assigned) with a mock consumer to test listener logic.
import time
from collections import defaultdict
class MockKafkaConsumer:
def __init__(self):
self.assignments = defaultdict(list)
self.rebalances = 0
def assign(self, partitions):
self.rebalances += 1
self.assignments.clear()
for partition in partitions:
s…How to Stream Join Windowed Mock Topics in Python
Simulates two message topics and joins their events when timestamps fall within a sliding time window using Python generators and deques.
import itertools
import random
import time
from collections import deque
from dataclasses import dataclass, field
@dataclass
class Event:
key: str
value: int
timestamp: float = field(default_factory=time.time)
def generate_topic(prefix, keys, start_time):
while True:
yield Event(
…Implement a retry queue with visibility timeout in Python
This code simulates a message queue with a visibility timeout, allowing messages to be retried if not deleted before the timeout expires.
import time
from collections import deque
class SimpleQueue:
def __init__(self, visibility_timeout=2):
self.queue = deque()
self.in_flight = {}
self.visibility_timeout = visibility_timeout
def send(self, message):
self.queue.append(message)
def receive(self):
if …Coalescing duplicate in-flight requests: one shared result for concurrent callers
Runs identical concurrent requests through a single shared call, caching the result while it's in flight and returning the same value to all callers.
import time
import threading
from collections import defaultdict
class CoalescingExecutor:
def __init__(self):
self._locks = defaultdict(threading.Lock)
self._in_flight = {}
def execute(self, key, func):
with self._locks[key]:
if key in self._in_flight:
re…How to Implement a Write-Through Cache in Python with a Mock Database
A thread-safe write-through cache that updates both cache and mock database atomically, computing values only after a successful write to the database.
import threading
import time
import random
class WriteThroughCache:
def __init__(self):
self.cache = {}
self.db = {}
self.lock = threading.Lock()
def write(self, key, value):
with self.lock:
# Simulate slow database write
time.sleep(random.uniform(0.01…How to Iterate Redis Keys with SCAN in Python
Iterate all Redis keys matching a pattern using the SCAN command with a mock client to simulate pagination.
import redis
def scan_keys(client, pattern="*", count=10):
keys = []
cursor = 0
while True:
cursor, batch = client.scan(cursor=cursor, match=pattern, count=count)
keys.extend(batch)
if cursor == 0:
break
return keys
if __name__ == "__main__":
# Mock Redis clien…How to Mock a Redis Transaction with MULTI/EXEC in Python
A minimal in-memory mock of Redis MULTI/EXEC transactions that queues commands and applies them atomically on EXEC.
class RedisTransactionMock:
def __init__(self):
self.data = {}
self.queue = []
self.in_transaction = False
def multi(self):
self.in_transaction = True
self.queue = []
return "OK"
def set(self, key, value):
if self.in_transaction:
self.qu…How to Use Redis HSET and HGET in Python
This code demonstrates how to store and retrieve hash data in Redis using Python's redis library with HSET, HGET, HGETALL, and HDEL commands.
import redis
# Connect to Redis (adjust host/port as needed)
r = redis.Redis(host='localhost', port=6379, db=0, decode_responses=True)
# Clear any existing data for demonstration
r.delete('user:1')
# HSET - Store a hash
r.hset('user:1', mapping={'name': 'Alice', 'age': 30, 'city': 'New York'})
# HGET - Retrieve a …How to Use lru_cache in Python for Cache-on-Miss Population
Demonstrates lru_cache to automatically populate cache on a miss and serve subsequent calls from cache, with cache info stats.
from functools import lru_cache
@lru_cache(maxsize=None)
def fetch_user(user_id):
"""Simulates a slow database fetch."""
print(f"Cache miss: fetching user {user_id} from database")
return {"id": user_id, "name": f"User {user_id}"}
if __name__ == "__main__":
user = fetch_user(1)
print(f"First call…How to memoize a function in Python with lru_cache
Use functools.lru_cache to memoize a recursive Fibonacci function, caching results for a fixed number of calls to avoid repeated computation.
from functools import lru_cache
@lru_cache(maxsize=128)
def fibonacci(n):
if n < 2:
return n
return fibonacci(n - 1) + fibonacci(n - 2)
if __name__ == "__main__":
for i in range(10):
print(f"fib({i}) = {fibonacci(i)}")
print(f"Cache info: {fibonacci.cache_info()}")How to use Redis MGET MSET pipeline in Python
Store multiple keys atomically and read them efficiently with Redis MSET/MGET, then batch commands with a pipeline to cut round trips.
import redis # v4.x+ required
r = redis.Redis(host="localhost", port=6379, db=0, decode_responses=True)
# Sample data to store
r.flushdb()
data = {"name": "Alice", "age": "30", "city": "Berlin"}
# MSET: store multiple key-value pairs in one command
r.mset(data)
# MGET: fetch multiple keys in one round trip
keys =…Browse by section
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