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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
How to Explode an Array Field into Multiple Rows in Python
This code flattens a list of dictionaries by exploding each array field value into its own row, duplicating the other fields as needed.
from collections import defaultdict
data = [
{"id": 1, "name": "Alice", "tags": ["python", "data", "ai"]},
{"id": 2, "name": "Bob", "tags": ["web", "devops"]},
{"id": 3, "name": "Carol", "tags": []},
]
def explode_array_field(records, array_field):
result = []
for record in records:
for v…How to Filter Data in Python
Filter a list of dictionaries by exact key-value matches or numerical ranges using concise list comprehensions.
from typing import List, Dict, Any
def filter_data(
data: List[Dict[str, Any]], key: str, value: Any
) -> List[Dict[str, Any]]:
"""Return records where data[key] equals value."""
return [record for record in data if record.get(key) == value]
def filter_by_range(
data: List[Dict[str, Any]], key: str…How to Group Data by Key in Python
Group a list of dictionaries by a specified key using a defaultdict and compute per-group averages.
from collections import defaultdict
def group_by_key(data, key):
grouped = defaultdict(list)
for item in data:
grouped[item[key]].append(item)
return dict(grouped)
if __name__ == "__main__":
records = [
{"name": "Alice", "dept": "Engineering", "score": 85},
{"name": "Bob", "de…How to Group Rows by Key into Nested Arrays in Python
This code groups rows in a list of dictionaries by a specified key and returns a dictionary with each key mapped to a list of values from another key.
from collections import defaultdict
def implode_rows(rows, key, value_key):
grouped = defaultdict(list)
for row in rows:
grouped[row[key]].append(row[value_key])
return dict(grouped)
if __name__ == "__main__":
data = [
{"category": "fruit", "item": "apple"},
{"category": "fr…How to Merge Incremental Snapshot Upsert Dict in Python
Merge a snapshot dict into a base dict, recursively updating nested dictionaries while preferring snapshot values on conflicts.
def merge_upsert(base: dict, snapshot: dict) -> dict:
"""
Merge a snapshot dict into a base dict, preferring snapshot values
on key conflicts (upsert semantics). Nested dicts are merged recursively.
"""
result = dict(base)
for key, value in snapshot.items():
if key in result and i…How to Merge Multiple Data Sources in Python
A beginner-friendly helper that merges lists of dictionaries from multiple sources into one combined list using key filtering.
import json
def merge_pipeline_data(*data_sources, keys=()):
"""Merge multiple data sources (list of dicts) into a single list of merged dicts.
Args:
*data_sources: One or more lists of dictionaries.
keys: Tuple of keys to include from each source (empty means all keys).
Returns:
…How to Partition Output Files by Date Key in Python
Group output files into a dictionary partitioned by a YYYYMMDD date key extracted from the filename prefix.
from pathlib import Path
from collections import defaultdict
def partition_files_by_date(directory: str) -> dict:
"""Partition output files by date key extracted from filename (YYYYMMDD prefix)."""
path = Path(directory)
partitions = defaultdict(list)
for file in path.iterdir():
if file.i…How to Reduce Aggregate Counts from Mapped Chunks in Python
Combine a list of mapped chunk dictionaries into a single aggregated count dictionary using functools.reduce.
from functools import reduce
from collections import defaultdict
def aggregate_chunks(mapped_chunks):
"""Combine mapped chunk counts into a single aggregate dict."""
return reduce(
lambda acc, chunk: {
**acc,
**{k: acc.get(k, 0) + v for k, v in chunk.items()}
},
…How to Sort a List of Dictionaries by Key in Python
A reusable helper function that sorts a list of dictionaries by a specified key, with optional descending order support.
from typing import List
def sort_records(records: List[dict], key: str, descending: bool = False) -> List[dict]:
"""Sort a list of dictionaries by a specified key."""
return sorted(records, key=lambda record: record[key], reverse=descending)
def demonstrate_sorting() -> None:
users = [
{"name": …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": "…Pivot long to wide transformation dict
Transform a list of dictionaries from long format to wide format by pivoting on a key column and aggregating values, using pure Python.
def pivot_long_to_wide(rows, key_col, value_col, id_cols=None):
"""
Convert long-format data (list of dicts) to wide format.
Args:
rows: List of dicts in long format
key_col: Column name to pivot on (becomes new column headers)
value_col: Column name whose values become the cel…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")
…Get Git Status Info in Python
Run git commands from Python to gather branch name, number of changes, total commits, and clean status, returning them as a dict.
import subprocess
import json
from pathlib import Path
def get_git_status(repo_path="."):
"""Return basic git info about a repository as a dict."""
try:
branch = subprocess.check_output(
["git", "branch", "--show-current"],
cwd=repo_path,
stderr=subprocess.DEVNULL,…How to Parse git status --porcelain Output in Python
This code runs `git status --porcelain` and parses its output into a list of dictionaries with file paths and status descriptions.
import subprocess
def parse_git_status_porcelain():
try:
output = subprocess.check_output(
["git", "status", "--porcelain"],
text=True,
stderr=subprocess.DEVNULL
)
except (subprocess.CalledProcessError, FileNotFoundError):
return []
entries = …How to Calculate Cloud Cost Estimates with a Python Dictionary
Mocks a cloud pricing calculator using a dictionary of service rates and computes total estimated cost for given service hours.
def estimate_cost(service, hours, rate_table=None):
if rate_table is None:
rate_table = {
"basic": 50,
"standard": 75,
"premium": 100
}
if service not in rate_table:
raise ValueError(f"Unknown service: {service}")
return rate_table[service] * hour…How to Convert Python Dict to JSON and Back
Convert Python dictionaries to JSON text and back with a simple helper that serializes and deserializes data structures.
import json
from datetime import datetime, timezone
def convert_data(data, source_format=None, target_format="json"):
"""
Convert Python data structures to txt/json and back.
For beginners: shows how to serialize/deserialize.
"""
if source_format == "json" and target_format == "dict":
ret…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 Evaluate IAM Policy Allow vs Deny in Python
Evaluate an AWS-style IAM policy dict with explicit deny overriding allow and default deny.
import json
def evaluate_policy(action, resource, policy):
"""Evaluate an IAM-like policy dict.
Explicit deny wins over allow. Default is deny.
"""
for statement in policy.get("Statement", []):
effect = statement.get("Effect")
actions = statement.get("Action", [])
resources = …How to Generate a Mock EKS Kubeconfig in Python
Generate a minimal kubeconfig dict with a mock EKS cluster entry and dump it to YAML using PyYAML.
import yaml
from pathlib import Path
def mock_eks_kubeconfig(cluster_name: str) -> dict:
"""Return a minimal kubeconfig dict with a mock EKS cluster entry."""
return {
"apiVersion": "v1",
"kind": "Config",
"clusters": [
{
"name": f"arn:aws:eks:us-east-1:123…How to Mock DynamoDB with a Simple Dict Store in Python
A lightweight in-memory DynamoDB mock that stores items in a dict and supports put, get, and query-by-value operations for local testing.
import json
from typing import Any, Dict, Optional
class MockDynamoDB:
def __init__(self) -> None:
self._store: Dict[str, Dict[str, Any]] = {}
def put_item(self, table_name: str, item: Dict[str, Any]) -> None:
key = str(item.get("id"))
if table_name not in self._store:
se…How to Mock ELB Target Health Status in Python
Simulate AWS Elastic Load Balancer target health checks with a Python dict that mutates status and healthy host counts.
from random import randint
def elb_target_mock_status(target_id, healthy=True):
targets = {
1: {"Id": "i-001", "Status": "healthy", "Port": 80, "HealthyHostCount": 1},
2: {"Id": "i-002", "Status": "unhealthy", "Port": 80, "HealthyHostCount": 0},
3: {"Id": "i-003", "Status": "healthy", "Por…How to Mock Pulumi Stack Outputs in Python
Create a dict-like mock of Pulumi stack outputs for local testing and scripts without running pulumi.
from collections import defaultdict
class StackOutputMock:
def __init__(self, outputs: dict):
self.outputs = dict(outputs)
def export(self):
return self.outputs
def get(self, key: str, default=None):
return self.outputs.get(key, default)
def keys(self):
r…How to Parse Cloud JSON Data in Python
A helper function that safely parses JSON payloads from cloud services into a clean dict with defaults and error handling.
import json
from typing import Dict, Any
def parse_cloud_data(payload: str) -> Dict[str, Any]:
"""Parse a JSON payload from a cloud service into a clean dict."""
try:
data = json.loads(payload)
return {
"status": data.get("status", "unknown"),
"region": data.get("region…How to Parse Terraform Output JSON in Python
Parse Terraform's JSON output into a flat dictionary of values using the standard library json module.
import json
def parse_terraform_output(raw_output):
"""Parse Terraform JSON output into a flat dict of values."""
try:
data = json.loads(raw_output)
except json.JSONDecodeError as e:
raise ValueError(f"Invalid JSON: {e}")
return {key: value["value"] for key, value in data.items()}
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