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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
How to Perform Intent-to-Treat Analysis in Python
Runs an intent-to-treat analysis on mock A/B test data, comparing outcomes by initial group assignment with a t-test for significance.
import pandas as pd
import numpy as np
def intent_to_treat_analysis(data):
"""Perform intent-to-treat (ITT) analysis.
ITT compares outcomes based on initial treatment assignment,
regardless of whether participants actually received the treatment.
"""
# Create a copy to avoid mutating the origina…How to Perform Welch's t-Test in Python
Calculate the Welch t-statistic and degrees of freedom for two samples with unequal variances using Python's statistics module.
import math
from statistics import mean, variance
def welch_t_test(sample1, sample2):
n1, n2 = len(sample1), len(sample2)
mean1, mean2 = mean(sample1), mean(sample2)
var1, var2 = variance(sample1), variance(sample2)
# Welch's t statistic
t_stat = (mean1 - mean2) / math.sqrt(var1 / n1 + var2 / n2…How to Run a Fisher Exact Test in Python
Compute the two-sided Fisher exact test p-value for a 2x2 contingency table using pure Python and the math module.
from math import comb, factorial
from itertools import combinations
def hypergeometric_probability(a, b, c, d):
"""Probability of observing table [[a, b], [c, d]] under the null."""
row1 = a + b
row2 = c + d
col1 = a + c
col2 = b + d
total = row1 + row2
return (comb(row1, a) * comb(row2, …How to Run a Permutation Test in Python
Run a Monte Carlo permutation test to compute a p-value for comparing two group means without parametric assumptions.
import random
import statistics
def permutation_test(group_a, group_b, n_permutations=10000, seed=42):
random.seed(seed)
combined = group_a + group_b
observed_diff = abs(statistics.mean(group_a) - statistics.mean(group_b))
count = 0
n = len(group_a)
for _ in range(n_permutations):
…How to Simulate Fixed-Horizon Testing in Python
Simulate a fixed-horizon experiment by labeling data before the horizon as warmup and after as active/inactive, then summarize via CSV.
import csv
import io
def fixed_horizon_mock(data: list[tuple[float, float, float]], horizon: int) -> str:
"""Simulate fixed-horizon testing, then summarize with CSV output."""
output = io.StringIO()
writer = csv.writer(output)
writer.writerow(["day", "value", "signal", "status"])
for day, value,…How to Simulate Geo Experiments in Python
Build a mock geo experiment simulator with ramp-up/down periods, measuring weekly lift between treatment and control markets.
import random
import math
from dataclasses import dataclass
@dataclass
class GeoMarket:
name: str
base_demand: float
geo_coefficient: float
def simulate_geo_experiment(markets, weeks=12, control_weeks=6):
"""
Simulates a geo experiment with ramp-up and ramp-down periods.
Returns weekly lift p…How to create a global control holdout group in Python
This code implements a deterministic global control holdout group, randomly selecting a fraction of users to be excluded from feature rollouts for experiment validation.
import random
class GlobalControl:
def __init__(self, population_size, holdout_fraction=0.2, seed=42):
random.seed(seed)
self.population_size = population_size
self.holdout_fraction = holdout_fraction
self.holdout_size = int(population_size * holdout_fraction)
self.holdout_…How to hash user IDs to experiment buckets in Python
Deterministically map a user ID to an experiment bucket using MD5 hashing, ensuring stable and consistent assignment for A/B testing.
import hashlib
def hash_user_to_bucket(user_id: str, num_buckets: int = 10) -> int:
"""Deterministically map a user ID to an experiment bucket (0..num_buckets-1)."""
digest = hashlib.md5(user_id.encode("utf-8")).hexdigest()
return int(digest, 16) % num_buckets
if __name__ == "__main__":
mock_users …How to join assignment logs with outcomes in Python
Merge submission log entries with grading outcomes using left join and full outer join patterns in pure Python.
from datetime import datetime, timedelta
class AssignmentLog:
def __init__(self):
self.logs = [
{"assignment_id": 101, "student_id": "S001", "submitted_at": "2024-03-01 10:30:00"},
{"assignment_id": 101, "student_id": "S002", "submitted_at": "2024-03-02 14:15:00"},
{"as…Simulate a Ramp Rollout Percentage in Python
Simulates a percentage-based ramp rollout with deterministic seeding, returning success/failure/in-progress counts for a mock user population.
import random
from enum import Enum
class RolloutStatus(Enum):
SUCCESS = "success"
FAILED = "failed"
IN_PROGRESS = "in_progress"
def simulate_ramp_rollout(total_users: int, percentage: int, seed: int = 42) -> dict:
"""
Simulates a mock ramp rollout for a given percentage of users.
Returns sta…Thompson Sampling Mock Bandit in Python
Implement a Thompson sampling multi-armed bandit to explore and exploit reward probabilities across multiple options, updating Beta distributions over time.
import random
class ThompsonSamplingBandit:
def __init__(self, num_arms, alpha=1.0, beta=1.0):
self.num_arms = num_arms
self.alpha = [alpha] * num_arms
self.beta = [beta] * num_arms
def select_arm(self):
samples = [random.betavariate(a, b) for a, b in zip(self.alpha, self.beta…UCB1 Bandit Algorithm in Python
This code implements the UCB1 multi-armed bandit algorithm, balancing exploration and exploitation to identify the best arm while maximizing cumulative reward.
import math
import random
def ucb1(means, n_iterations=1000, exploration_weight=2.0):
"""Run UCB1 bandit algorithm on arms with given true means."""
n_arms = len(means)
counts = [0] * n_arms
rewards = [0.0] * n_arms
for t in range(1, n_iterations + 1):
# UCB1 selection
if t <…How to Avoid SELECT * and Mock SQL Column Queries in Python
Mock a SQLite cursor to verify that queries specify explicit columns instead of using SELECT *.
import sqlite3
from unittest.mock import Mock, patch
def get_user_emails(connection):
"""Fetch only the required columns instead of SELECT *."""
cursor = connection.cursor()
cursor.execute("SELECT email FROM users")
return [row[0] for row in cursor.fetchall()]
def test_get_user_emails_specific_colu…How to Mock SQLite executemany When Batch Inserting in Python
Batch insert many rows into SQLite with executemany and mock the cursor for isolated tests.
import sqlite3
from unittest.mock import Mock, patch
def insert_users(conn, users):
"""Insert multiple user records using executemany."""
cursor = conn.cursor()
cursor.executemany(
"INSERT INTO users (name, age) VALUES (?, ?)",
users
)
conn.commit()
return cursor.rowcount
if _…How to Mock a Hot Shard Split in Python
Simulate a database hot shard splitting into two shards by key ranges when it exceeds a threshold, with a mock class for testing.
import random
from collections import defaultdict
class HotShardMock:
"""Mock implementation of a hot shard split in a distributed database."""
def __init__(self, shard_id="shard_1", max_entries=5):
self.shard_id = shard_id
self.max_entries = max_entries
self.entries = {}
def ad…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 …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…Build a Mock OIDC Userinfo Endpoint in Python with Flask
Create a local mock OIDC userinfo endpoint in Flask that returns a standard JSON user payload, ideal for testing auth flows without a real identity provider.
from flask import Flask, jsonify
app = Flask(__name__)
@app.route("/userinfo")
def userinfo():
mock_user = {
"sub": "1234567890",
"name": "John Doe",
"email": "john@example.com",
"email_verified": True,
"groups": ["admin", "dev"]
}
return jsonify(mock_user)
if __n…How to Mock Environment Variables in Python
A context manager that injects and restores environment variables for isolated testing of config-dependent code.
import os
class EnvInjector:
def __init__(self, mock_vars=None):
self.mock_vars = mock_vars or {}
self.original = {}
def __enter__(self):
for key, value in self.mock_vars.items():
if key in os.environ:
self.original[key] = os.environ[key]
os.env…How to Mock Environment Variables in Python for 12-Factor Config
Read 12-factor config from env vars and test/mock them with unittest.mock.patch.dict without touching the real environment.
import os
import json
from unittest.mock import patch
def load_config(env_prefix="APP"):
"""Read 12-factor style config from env vars"""
required = ["DATABASE_URL", "API_KEY"]
optional = {"PORT": "8080", "DEBUG": "false"}
config = {}
for key in required:
full_key = f"{env_prefix}_{key…How to Mock HTTP Responses to Verify HSTS Headers in Python
This code demonstrates how to use unittest.mock to intercept and capture HTTP response headers, specifically the Strict-Transport-Security header, from a mocked HTTPServer handler for security validation.
from http.server import BaseHTTPRequestHandler, HTTPServer
from unittest.mock import patch
class StrictTransportMock(BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(200)
self.send_header("Strict-Transport-Security", "max-age=31536000; includeSubDomains")
self.end_headers()
…How to Mock OAuth 2.0 Device Code Flow in Python
A mock implementation of the OAuth 2.0 device authorization grant for testing authentication flows without a real provider.
import hashlib
import time
import uuid
class DeviceCodeFlowMock:
def __init__(self):
self.device_codes = {}
def request_device_code(self, client_id, scope="read write"):
device_code = uuid.uuid4().hex
user_code = str(uuid.uuid4().int)[:8].upper()
expires_in = 300
inte…How to Mock a Content Security Policy Header in Python
Mock a Content-Security-Policy header locally and verify it's served correctly using Python's built-in HTTP server.
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
CSP_HEADER = "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'"
class MockServer(BaseHTTPRequestHandler):
def do_GET(self):
if self.path == "/":
self.send_response(200)
self.send_header("…How to Mock a Redis Session Store in Python
An in-memory RedisSessionStore class with TTL-based expiry, get/set/delete/exists methods, and JSON field support—perfect for testing and prototyping without a live Redis.
import time
import json
from collections import defaultdict
class RedisSessionStore:
"""In-memory mock of a Redis-backed session store."""
def __init__(self, ttl=3600):
self._data = defaultdict(dict)
self._expires = {}
self._ttl = ttl
def set(self, session_id, field, value):
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