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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
How to Mock a Cross-Shard Saga in Python
Simulate a distributed saga with compensating transactions across multiple database shards using a lightweight Python class that tracks executed steps and rolls them back in reverse on failure.
import json
class SagaState:
def __init__(self, saga_id):
self.saga_id = saga_id
self.executed_steps = []
self.compensations = []
def execute_step(self, shard, step_name, operation):
self.executed_steps.append((shard, step_name))
print(f"[Saga {self.saga_id}] Executin…How to Mock a Function Call in Python with unittest.mock
Use unittest.mock.Mock to wrap a function and spy on its call count and arguments in Python.
import random
from unittest.mock import Mock, patch
def select_n_plus_one(numbers: list[int]) -> int:
"""Return the first number that appears more than once, if any."""
seen = set()
for num in numbers:
if num in seen:
return num
seen.add(num)
return -1
def detect_mock(se…How to Optimize SQLite Database Performance in Python
A Python helper that creates an index, enables WAL mode, and tunes synchronous settings to optimize SQLite database performance.
import sqlite3
DATABASE_PATH = "beginners.db"
UNOPTIMIZED_TABLE_SCHEMA = """
CREATE TABLE IF NOT EXISTS users (
id INTEGER PRIMARY KEY,
name TEXT NOT NULL,
email TEXT NOT NULL
)
"""
def optimize_database(db_path: str = DATABASE_PATH) -> dict:
with sqlite3.connect(db_path) as connection:
curs…How to Replicate Data Across All Shards in Python
Mocks a global table that replicates a key-value pair to every shard, ensuring reads return the same value from any shard.
from dataclasses import dataclass
from typing import Dict, List
@dataclass
class Shard:
id: str
data: Dict[str, int]
class GlobalTable:
def __init__(self, shards: List[Shard]):
self._shards = {s.id: s for s in shards}
def set_value(self, key: str, value: int) -> None:
"""Replicate …How to Simulate Colocated Shard Joins in Python
Groups shards by their node and merges co-located shards into a single logical unit, checking capacity constraints.
import random
from collections import defaultdict
def simulate_colocated_shards_join(nodes: list[dict], shards: list[dict]) -> dict:
"""
Simulates the join of co-located shards (on the same node) into a single
logical shard. Returns the resulting node-to-shard mapping.
Each node: {'id': str, 'capaci…How to Simulate Distributed Transactions in Python with a Mock
Model distributed transaction behavior with a mock Transaction class that supports commit, rollback, and failure simulation.
class Transaction:
def __init__(self, id):
self.id = id
self.operations = []
self.committed = False
def add_operation(self, op, data):
self.operations.append((op, data))
def commit(self):
if not self.operations:
raise ValueError("No operations to commit…How to Validate Data Before Scaling in Python
A reusable Python helper that validates required fields and constraint checks on data rows before entering a database pipeline, improving data quality and throughput.
def validate_data(data, required_fields, constraints=None):
"""
Basic validation helper demonstrating data-quality workflows
before scaling (catches bad rows early, improves throughput).
"""
constraints = constraints or {}
errors = []
for field in required_fields:
if field not in d…How to mock batch commit of transactions in Python
Simulate a transaction batch writer with commit, rollback, and summary logic to test database write patterns without a real database.
import json
from datetime import datetime, timezone
class TransactionBatch:
def __init__(self):
self.pending = []
self.committed = []
self._log = []
def add(self, operation):
self.pending.append(operation)
def commit(self):
if not self.pending:
return …How to mock directory-based sharding in Python
Simulates distributing files into logical shards using a deterministic hash of each filename, mocking how a database might shard rows across nodes.
import os
import hashlib
from collections import defaultdict
from pathlib import Path
def get_shard_for_key(key: str, num_shards: int) -> int:
"""Return a deterministic shard index (0..num_shards-1) for a key."""
digest = hashlib.md5(key.encode('utf-8')).hexdigest()
return int(digest, 16) % num_shards
…Mock CQRS Read/Write Split in Python
Separate order mutations from queries using a read model and write model to mock CQRS-style separation of concerns.
from dataclasses import dataclass, field
from typing import List, Dict
@dataclass
class Order:
id: int
amount: float
status: str = "pending"
class OrderWriteModel:
"""Handles all mutations (writes) to orders."""
def __init__(self):
self._orders: Dict[int, Order] = {}
self._next…Monitor Database Index Bloat in Python
Simulates index bloat checks for database tables using random ratio thresholds and reports alerts per index.
import random
import time
class IndexBloatMonitor:
def __init__(self, thresholds=(0.5, 0.8, 0.9)):
self.thresholds = thresholds
self.indices = {
"users_pk": 48.2,
"orders_created_idx": 124.7,
"products_name_idx": 15.3,
"payments_user_idx": 203.9,
…Offset vs Keyset Pagination in Python
Demonstrate offset-based pagination and keyset (cursor) pagination with a simple in-memory dataset, showing how each returns pages of records.
"""Demonstrate pagination using offset vs keyset (cursor) approach."""
ITEMS = [
{"id": 1, "name": "Alice"},
{"id": 2, "name": "Bob"},
{"id": 3, "name": "Carol"},
{"id": 4, "name": "David"},
{"id": 5, "name": "Eve"},
]
def offset_paginate(items, page, page_size):
"""Return a page using offset…Rebalance Shard Ranges Across Nodes in Python
A mock rebalancing function that shuffles shard ranges and distributes them evenly across nodes using round-robin assignment.
import random
from dataclasses import dataclass
@dataclass
class Shard:
id: int
start: int
end: int
def rebalance_shards(shards: list[Shard], node_count: int) -> dict[int, list[Shard]]:
"""Mock rebalancing of shard ranges across nodes."""
all_ranges = [(s.start, s.end) for s in shards]
random…Route SELECT Queries to Read Replicas in Python
A mock round-robin router that forwards SELECT queries to read replicas and sends writes to the primary.
import random
class ReadReplicaRouter:
"""Round-robin router that sends SELECT queries to read replicas."""
def __init__(self, replicas):
self.replicas = replicas
self.counter = 0
def route(self, sql):
if sql.strip().upper().startswith("SELECT"):
replica = sel…Simulate PostgreSQL Vacuum to Reclaim Space in Python
A Python class that safely rewrites a data file to remove deleted rows and reclaim physical space, mimicking PostgreSQL's VACUUM operation.
import shutil
import os
class VacuumCleaner:
"""Simulates PostgreSQL-style vacuum reclaiming dead space in a file."""
def __init__(self, filepath, fill_ratio=0.7, dead_marker="[DELETED]"):
self.filepath = filepath
self.fill_ratio = fill_ratio
self.dead_marker = dead_marker
…Simulate Shard Key Cardinality in Python
Generate mock data with configurable cardinality to evaluate shard key distribution and detect hotspots in database scaling design.
import random
import string
def calculate_cardinality(values):
"""Return the number of distinct values in the given list."""
return len(set(values))
def generate_mock_data(num_records, cardinality):
"""Generate mock records for a shard key with given cardinality."""
possible_keys = [f"key_{i:04d}" fo…Snowflake ID Generator with Cluster Index Mock in Python
A thread-safe Snowflake ID generator mock that creates unique 64-bit IDs across simulated cluster nodes and maintains a sorted in-memory index for range queries.
import time
import threading
class SnowflakeIDGenerator:
def __init__(self, machine_id, datacenter_id):
self.machine_id = machine_id
self.datacenter_id = datacenter_id
self.sequence = 0
self.last_timestamp = -1
self.machine_bits = 5
self.datacenter_bits = 5
…Two Phase Commit Cross Shard Mock in Python
Simulates a two-phase commit across shards with failure handling to demonstrate distributed transaction coordination in Python.
"""Mock cross-shard two-phase commit with caution handling."""
class Shard:
def __init__(self, name):
self.name = name
self.prepared = False
self.committed = False
self.aborted = False
def prepare(self):
# Simulate potential failure (1 in 3 chance on third shard)
…UUID vs sequential primary key in Python
Simulate and compare UUID vs sequential primary key generation in Python to understand trade-offs in ordering and uniqueness.
import uuid
import time
def create_record_with_uuid(name):
record_id = uuid.uuid4()
return {"id": record_id, "name": name}
def create_record_with_sequential_id(name, counter):
counter += 1
return {"id": counter, "name": name}
if __name__ == "__main__":
# Simulate users inserting records
sequ…ACME LetsEncrypt Mock Challenge Server in Python
A minimal HTTP server that serves key authorizations for ACME/Let's Encrypt DNS-01 or HTTP-01 challenges during testing and validation.
from http.server import HTTPServer, BaseHTTPRequestHandler
import json
# In-memory store simulating the ACME challenge token -> key authorization pair
challenge_store = {
"token_example": "token_example.key_authorization"
}
class AcmeChallengeHandler(BaseHTTPRequestHandler):
def do_GET(self):
# Extra…AES GCM encryption and decryption in Python
Encrypt and decrypt data with AES-256-GCM using the cryptography library, including nonce generation and authenticated roundtrip verification.
import os
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
def aes_gcm_demo():
plaintext = b"confidential message"
key = AESGCM.generate_key(bit_length=256)
aesgcm = AESGCM(key)
nonce = os.urandom(12)
ciphertext = aesgcm.encrypt(nonce, plaintext, None)
decrypted = aesgcm.dec…ChaCha20-Poly1305 mock in Python
Simulates ChaCha20-Poly1305 AEAD encryption and authentication using SHA-256 as a deterministic keystream and tag generator.
from hashlib import sha256
import struct
def chacha20_block(key, counter, nonce):
"""Mock ChaCha20 block: deterministic pseudo-random keystream from key+counter+nonce."""
state_input = key + struct.pack("<I", counter) + nonce + b"ChaCha20"
return sha256(state_input).digest()[:64] # 64-byte keystream bloc…Enforce TLS 1.2 Minimum in Python
Create an SSL context with a minimum TLS version of 1.2 to enforce secure connections.
import ssl
def get_min_tls_version():
context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
context.minimum_version = ssl.TLSVersion.TLSv1_2
return context.minimum_version
if __name__ == "__main__":
min_version = get_min_tls_version()
print(f"Minimum TLS version set to: {min_version.name} (value: {mi…How to Check Negotiated Cipher Suite in Python
Connect to a TLS server with Python's ssl module and print the negotiated protocol version and cipher suite details.
import ssl
import socket
def get_cipher_suites(hostname, port=443):
context = ssl.create_default_context()
context.set_ciphers("DEFAULT:@SECLEVEL=2")
with socket.create_connection((hostname, port), timeout=5) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
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