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How to Implement Slowly Changing Dimension Type 2 History in Python
Build a type-2 slowly changing dimension pipeline that closes old records and opens new ones when customer data changes.
from datetime import datetime, timedelta
def apply_scd_type2(records, current_date):
"""Returns active records after inserting new records with type-2 history."""
history = []
active = {}
for record in records:
key = record["customer_id"]
if key in active:
active[key]["end…How to Process CSV Data in Python with a Data Helper
Build a beginner-friendly data helper in Python that loads a CSV file, filters rows by a condition, and summarizes numeric fields.
import csv
from pathlib import Path
DATA = [
{"name": "Alice", "score": 88, "passed": True},
{"name": "Bob", "score": 42, "passed": False},
{"name": "Carol", "score": 95, "passed": True},
]
def load_csv(file_path: Path) -> list[dict]:
with file_path.open(newline="", encoding="utf-8") as f:
r…How to perform a star schema join in Python
Denormalize mock fact and dimension tables by building lookup dicts and enriching each sales fact with customer, product, and date attributes.
from datetime import date
# Mock dimension tables
customers = [
{"customer_id": 1, "name": "Alice", "city": "New York"},
{"customer_id": 2, "name": "Bob", "city": "Los Angeles"},
{"customer_id": 3, "name": "Carol", "city": "Chicago"},
]
products = [
{"product_id": 101, "name": "Laptop", "category": "…Test a Python Pipeline with Fixture Sample Rows
Test pipeline functions with sample rows provided by a pytest fixture, verifying required keys and value constraints.
import pytest
def get_value(data: dict, key: str):
return data.get(key)
def sample_rows():
return [
{"name": "Alice", "age": 30, "city": "London"},
{"name": "Bob", "age": 25, "city": "Paris"},
{"name": "Charlie", "age": 35, "city": "Berlin"},
]
@pytest.fixture
def sample_data(…Validate dict schema at pipeline boundary in Python
This code validates a dictionary against a TypedDict schema at a pipeline boundary, enforcing required fields and types with custom error messages.
from typing import Any, TypedDict
class Person(TypedDict):
name: str
age: int
email: str
def validate_person(data: dict[str, Any]) -> Person:
errors: list[str] = []
if not isinstance(data.get("name"), str) or not data["name"].strip():
errors.append("name must be a non-empty string")
…Build a Simple Log Graph in Python
Create a basic one-dimensional bar chart from log lines by counting occurrences of leading numeric keys.
import heapq
def log_graph(log_lines: list[str]) -> str:
"""Build a simple per-line, one-dimensional visual graph from log entries."""
counts: dict[int, int] = {}
for line in log_lines:
tokens = line.split()
if tokens:
try:
idx = int(tokens[0])
exce…Create a Mock GitHub Release API in Python for Testing gh CLI
Build an in-memory GitHub Releases API mock that mimics create_release and list_releases for unit testing gh CLI stubs without network calls.
import json
from unittest.mock import patch, Mock
class GitHubReleaseAPI:
"""Mock GitHub Releases API for testing gh CLI stub behavior."""
def __init__(self):
self.releases = {}
self.counter = 1
def create_release(self, repo, tag, name=None, notes=None):
release_id = self…How to Build a Branch Protection Audit Mock API in Python
A mock HTTP API that serves branch protection rules for repositories and audits them for compliance, built with Python's standard library.
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
from urllib.parse import urlparse, parse_qs
REPOSITORIES = {
"alpha": {
"default_branch": "main",
"branches": ["main", "develop", "feature-x"],
"protection_rules": {
"main": {"required_reviews": 2, "dismiss_…How to Build a Git Helper Class in Python
A beginner-friendly GitHelper class that wraps common git commands (status, log, branch) into reusable Python methods with structured output.
import subprocess
import json
from pathlib import Path
class GitHelper:
def __init__(self, repo_path="."):
self.repo = Path(repo_path)
def run(self, *args):
result = subprocess.run(
["git", *args],
cwd=self.repo,
capture_output=True,
text=True,…How to Create a Git Commit with Message Template in Python
Run a git commit from Python using a standardized message template built from a commit type and description.
import subprocess
import sys
def commit_with_template(commit_type: str, description: str) -> None:
message = f"{commit_type}: {description}"
try:
subprocess.run(["git", "commit", "-m", message], check=True)
print(f"Committed: {message}")
except subprocess.CalledProcessError as e:
…How to Generate Git LFS Extension Patterns in Python
This script builds mock Git LFS file patterns for common geospatial extensions and filters them based on compression suffixes.
import itertools
import re
LFS_EXTENSIONS = {".csv", ".geojson", ".tif", ".shp", ".gpkg"}
def build_mock_lfs_pattern(base_name="data_usgs_lidar"):
patterns = []
for ext in sorted(LFS_EXTENSIONS):
for variant in (("", ".lz4"), (".compressed",), (".b", ".a"), ("_v1", ".zip")):
full_pattern …How to Mock subprocess.run in Python Tests
Mock subprocess.run to test a Git submodule update command without executing it in your test suite.
import subprocess
from unittest.mock import Mock, patch
def update_submodules():
subprocess.run(["git", "submodule", "update", "--init", "--recursive"], check=True)
with patch("subprocess.run") as mock_run:
mock_run.return_value = Mock(returncode=0)
update_submodules()
mock_run.assert_called_once_wit…Build a URL Shortener Client with Python
A Python class that shortens long URLs and resolves short codes using a REST API built with requests.
import json
import sys
import requests
class URLShortenerClient:
def __init__(self, base_url="http://tinyurl.com"):
self.base_url = base_url
def shorten_url(self, long_url):
payload = {"url": long_url}
headers = {"Content-Type": "application/json"}
response = requests.post(f"{…Create a Cloud Storage Helper Class in Python
Build a simple local file-based helper class that mimics cloud storage operations like save, load, and list JSON objects.
import datetime
import json
from pathlib import Path
class CloudDataHelper:
"""Simple helper for reading/writing JSON files in a cloud-style folder."""
def __init__(self, base_dir: str = "cloud_storage"):
self.base_dir = Path(base_dir)
self.base_dir.mkdir(exist_ok=True)
def save_json(se…Generate a Mock Presigned URL in Python with HMAC
Build a mock AWS S3 presigned URL using an HMAC-SHA256 signature, mimicking the core SigV4 pattern without cloud SDK dependencies.
import hashlib
import hmac
import time
import base64
def generate_presigned_url_mock(secret_key, bucket, object_key, expires_in=3600):
# Build the canonical request string (simplified AWS SigV4 style)
timestamp = str(int(time.time()))
expiry = str(int(time.time()) + expires_in)
payload = f"GET\n/{buck…Generate an Idempotency-Key header mock with UUID in Python
This code provides a mock idempotency service that generates a UUID-based Idempotency-Key header token and validates it, useful for simulating production API behavior in tests.
import uuid
class MockIdempotencyService:
def __init__(self):
self._tokens = {}
def get_token(self, header_name="Idempotency-Key"):
token = str(uuid.uuid4())
self._tokens[header_name] = token
return token
def validate(self, header_name="Idempotency-Key"):
return s…How to Build a Budget Alert Threshold with Mock Notifications in Python
This code calculates budget usage percentage and triggers a mock alert notification when the usage exceeds a defined threshold.
budget = 500.0
spent = 620.0
alert_threshold = 0.8
def mock_notify(percent_used):
if percent_used >= alert_threshold:
return f"ALERT: Budget usage at {percent_used * 100:.1f}% — over {alert_threshold * 100:.0f}% threshold!"
return f"OK: Budget usage at {percent_used * 100:.1f}% — under threshold."
pe…How to Build a Multi-Cloud Config Loader with Provider Switching in Python
Load cloud provider configurations (AWS, Azure, GCP) from JSON files using a provider dispatch pattern in Python.
import json
from pathlib import Path
from dataclasses import dataclass
from typing import Dict, Any
@dataclass
class CloudConfig:
provider: str
region: str
settings: Dict[str, Any]
class ConfigLoader:
def __init__(self, config_dir: str = "configs"):
self.config_dir = Path(config_dir)
…How to Create a Mock STS AssumeRole Credentials Dict in Python
Build a realistic AWS STS AssumeRole response dict with temporary credentials, expiry time, and assumed role ARN for local testing.
import json
from datetime import datetime, timedelta, timezone
def mock_sts_credentials(role_arn, session_name, duration=3600):
now = datetime.now(timezone.utc)
expiration = now + timedelta(seconds=duration)
credentials = {
"Credentials": {
"AccessKeyId": "ASIAEXAMPLEACCESSKEY",
…How to Enforce Tag Policies on AWS Resources in Python
Build a reusable Python class that checks AWS resources against a required-tag policy and reports compliance with missing tags.
import json
from dataclasses import dataclass, field
from typing import Dict, List
@dataclass
class Resource:
arn: str
tags: Dict[str, str] = field(default_factory=dict)
class TagPolicyEnforcer:
def __init__(self, required_tags: List[str]):
self.required_tags = set(required_tags)
def enfor…How to Mock AWS SQS Send Receive Delete in Python
Build an in-memory mock of the SQS send, receive, and delete message flow for local testing.
import json
from collections import deque
from uuid import uuid4
class MockSQSQueue:
def __init__(self, name):
self.name = name
self._messages = deque()
self._in_flight = {}
def send_message(self, body, attributes=None):
message_id = str(uuid4())
message = {
…How to Mock CloudFront Invalidation Paths in Python
Build a sorted, deduplicated list of CloudFront invalidation paths from a set of file paths, adding implicit index.html entries.
import argparse
def build_invalidation_paths(files, include_index=True):
"""
Create CloudFront invalidation paths from a list of files.
Converts file names to root-relative paths and optionally adds /index.html.
"""
paths = []
for f in files:
f = f.strip()
if not f:
…How to Validate Data Fields and Types in Python
Validate required fields and type correctness in a Python dictionary with small helper functions, returning a list of clear error messages.
import json
from typing import Any, Dict, List
def validate_data(data: Dict[str, Any], required_fields: List[str]) -> List[str]:
"""Check required fields exist and are non-empty. Return list of errors."""
errors = []
for field in required_fields:
value = data.get(field)
if value is None o…Mock ECS Task Run Stop Status Dict in Python
Build a mock ECS task status dictionary with RUNNING/STOPPED states using the standard library.
from datetime import datetime, timezone
def mock_ecs_task_status(task_id: str, state: str = "RUNNING") -> dict:
"""Return a mock ECS task status dictionary."""
return {
"taskArn": f"arn:aws:ecs:us-east-1:123456789012:task/cluster/{task_id}",
"taskDefinition": "arn:aws:ecs:us-east-1:1234567890…Browse by section
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