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How to Bulk Insert Rows into SQLite in Python
Insert many rows into an SQLite table in one call with cursor.executemany, then verify them with a SELECT query.
import sqlite3
# Create an in-memory database and a table
conn = sqlite3.connect(":memory:")
cursor = conn.cursor()
cursor.execute("CREATE TABLE products (name TEXT, price REAL, quantity INTEGER)")
# Data to insert in bulk
products = [
("Laptop", 999.99, 5),
("Mouse", 19.99, 50),
("Keyboard", 49.99, 30),…How to Find HTML Elements by Tag, Class, ID, CSS Selector, and Attribute in BeautifulSoup
Parse an HTML string with BeautifulSoup and demonstrate five distinct ways to locate elements: by tag name, by class, by ID, by CSS selector, and by attribute.
from bs4 import BeautifulSoup
html_content = """
<html><body>
<h1 id="title" class="heading">Hello World</h1>
<p class="content">First paragraph</p>
<p class="content special">Second paragraph</p>
<a href="https://example.com" class="link">Click here</a>
<div id="footer">
<p>© 2024</p>
…How to Normalize Data in Python with Dictionaries and Sets
Normalize a list of dicts by keeping selected keys, stripping/lowercasing strings, and extracting unique sorted values using set comprehension.
def normalize_data(data, keys):
"""
Normalize a list of dictionaries by keeping only specified keys
and converting values to proper types.
"""
normalized = []
for item in data:
clean_item = {}
for key in keys:
value = item.get(key)
if isinstance(value, st…How to Sample Random Items Without Replacement in Python
Select k random unique items from a sequence using random.sample for uniform, non-repeating selection.
import random
def sample_without_replacement(population, k):
"""Return k random items from population without replacement."""
if k > len(population):
raise ValueError("k cannot exceed population size")
# Use random.sample for O(k) time, no mutation of the original
return random.sample(populati…Pick a Random Region with Mock Carbon Intensity in Python
Selects a random region from a list and generates a mock carbon intensity value using Python's random module.
import random
def pick_region_intensity(regions, seed=42):
random.seed(seed)
selected = random.choice(regions)
intensity = random.randint(1, 10)
return selected, intensity
if __name__ == "__main__":
regions = ["North", "South", "East", "West"]
selected, intensity = pick_region_intensity(regio…How to Create Interactive CLI Prompts in Python with questionary
Build mock interactive command-line prompts using questionary's select and text widgets with graceful handling of user cancellation.
import questionary
def main():
# Mock interactive prompts using questionary's select and text
choice = questionary.select(
"What is your favorite programming language?",
choices=["Python", "JavaScript", "Go", "Rust"]
).ask()
# ask() returns None if user cancels; handle gracefully
…How to configure ruff linter rules in pyproject.toml with Python
This Python script generates a pyproject.toml file with ruff linter rules, including selected and ignored rules, per-file ignores, and complexity limits.
from pathlib import Path
def configure_ruff_rules(project_dir: str = "my_project") -> None:
"""Create a pyproject.toml with ruff linter rules for mock usage."""
pyproject_path = Path(project_dir) / "pyproject.toml"
pyproject_path.parent.mkdir(parents=True, exist_ok=True)
config = """[tool.ruff]
line-…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 Skip Slow Tests with pytest.mark in Python
Use pytest.mark.skip and custom marks like @pytest.mark.slow to skip or deselect slow tests during test runs.
import pytest
import time
def test_fast():
assert 1 + 1 == 2
@pytest.mark.skip(reason="slow test skipped by default")
def test_slow():
time.sleep(5)
assert True
@pytest.mark.slow
def test_marked_slow():
time.sleep(5)
assert True
if __name__ == "__main__":
pytest.main([__file__, "-v", "-…How to Build a Weighted Random Load Balancer in Python
A Python load balancer mock that distributes requests across servers based on configurable weights using a cumulative weighted random selection algorithm.
import random
from collections import Counter
SERVERS = {
"server-a": 50,
"server-b": 30,
"server-c": 20,
}
def weighted_random_server(servers: dict[str, int]) -> str:
"""Select a server based on its weight (higher weight = more likely)."""
total_weight = sum(servers.values())
rand = random.…Mock NATS queue group load balancing in Python
Simulates a NATS queue group where each message is delivered to exactly one subscriber using random selection with a lightweight mock.
import random
import time
from collections import defaultdict
class MockQueueGroup:
"""Mock a NATS queue group: each message is delivered to exactly one subscriber."""
def __init__(self, subscribers):
self.subscribers = subscribers
def publish(self, message):
receiver = random.choice(se…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 Filter and Project Spark DataFrames with PySpark SQL
Simulate a SQL SELECT with WHERE using PySpark DataFrame select and filter to project columns and apply conditions.
from pyspark.sql import SparkSession
from pyspark.sql.functions import col
spark = SparkSession.builder.appName("QueryFilterMock").master("local[2]").getOrCreate()
data = [
("Alice", 28, "Engineering"),
("Bob", 35, "Sales"),
("Carol", 32, "Engineering"),
("David", 25, "Marketing"),
("Eve", 29, "E…How to select specific columns in Python with SQLite
A reusable function that connects to a SQLite database and returns only the requested columns from a given table.
import sqlite3
def select_pruned_columns(db_path, table, columns):
with sqlite3.connect(db_path) as conn:
cursor = conn.cursor()
col_list = ", ".join(columns)
query = f"SELECT {col_list} FROM {table}"
return cursor.execute(query).fetchall()
if __name__ == "__main__":
conn = sq…How to do feature selection with VarianceThreshold in Python
This code demonstrates how to use scikit-learn's VarianceThreshold to remove low-variance features from a NumPy array, keeping only those that vary enough to be useful for modeling.
import numpy as np
from sklearn.feature_selection import VarianceThreshold
def main():
# Mock dataset: 4 samples, 5 features
X = np.array([
[0.1, 0.2, 1.0, 1.0, 0.5],
[0.2, 0.2, 0.0, 1.0, 0.4],
[0.1, 0.2, 1.0, 1.0, 0.6],
[0.3, 0.2, 1.0, 0.0, 0.5]
])
# Select features w…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 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…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…How to Replace Fields in an Immutable Dataclass in Python
Create a new copy of a frozen dataclass with selected fields changed, leaving the original unchanged.
from dataclasses import dataclass, replace
@dataclass(frozen=True)
class ServerConfig:
name: str
cpu: int = 2
ram: int = 4096
tags: tuple = ()
original = ServerConfig("web-01", cpu=4, tags=("env:prod",))
updated = replace(original, ram=8192, tags=("env:prod", "region:us-east"))
print("Original:", …Browse by section
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