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How to Memoize Pure Functions with functools.lru_cache in Python
Use functools.lru_cache to memoize a pure Fibonacci function and avoid recomputing repeated values.
from functools import lru_cache
@lru_cache(maxsize=128)
def fibonacci(n: int) -> int:
"""Return the nth Fibonacci number (0-indexed) using memoization."""
if n < 2:
return n
return fibonacci(n - 1) + fibonacci(n - 2)
if __name__ == "__main__":
for i in range(10):
print(f"fibonacci({…How to Run an Async Main with asyncio.run in Python
Show the canonical entry point for an asyncio program: define an async main, then launch it with asyncio.run.
import asyncio
async def main():
print("Hello from async main")
await asyncio.sleep(0.1)
print("Done")
if __name__ == "__main__":
asyncio.run(main())How to Signal asyncio Workers to Stop with an Event in Python
Use an asyncio.Event to coordinate graceful shutdown of multiple concurrent worker tasks in Python.
import asyncio
import random
async def worker(name, stop_event):
while not stop_event.is_set():
await asyncio.sleep(random.uniform(0.1, 0.5))
print(f"Worker {name} processing...")
print(f"Worker {name} stopped.")
async def main():
stop_event = asyncio.Event()
workers = [asyncio.create…How to Use Array Typecodes for Compact Numeric Storage in Python
This code demonstrates how to use the `array` module with typecodes to store integers, floats, and bytes in a memory-efficient way compared to standard Python lists.
from array import array
def demonstrate_array_types():
# Compact integer arrays
small_ints = array('i', [1, 2, 3, 4, 5])
unsigned_ints = array('I', [10, 20, 30])
# Floating point arrays
floats = array('f', [1.5, 2.5, 3.5])
doubles = array('d', [1.123456789, 2.987654321])
# Charac…How to Use bisect.insort in Python to Maintain a Sorted List
Insert items into an already sorted list using Python's bisect.insort to keep it sorted efficiently in O(n) time.
import bisect
def maintain_sorted_list():
data = [3, 1, 4, 1, 5, 9, 2, 6]
sorted_list = []
for num in data:
bisect.insort(sorted_list, num)
print("Original data:", data)
print("Sorted list maintained with insort:", sorted_list)
# Insert new values to maintain sorted orde…How to Use uvloop Faster Event Loop
Install uvloop at startup to replace asyncio's default event loop with a faster libuv-based one, with a graceful fallback when it's unavailable.
import asyncio
try:
import uvloop
uvloop.install()
USING_UVLOOP = True
except ImportError:
USING_UVLOOP = False
async def fetch_data(index):
await asyncio.sleep(0.01)
return f"data-{index}"
async def main():
tasks = [fetch_data(i) for i in range(10)]
results = await asyncio.gather(*…How to set a timeout with asyncio.wait_for in Python
Use asyncio.wait_for to bound an async function with a timeout, catching TimeoutError when it exceeds the limit.
import asyncio
async def slow_task():
await asyncio.sleep(3)
return "finished"
async def main():
try:
result = await asyncio.wait_for(slow_task(), timeout=1)
print(result)
except asyncio.TimeoutError:
print("Task timed out")
if __name__ == "__main__":
asyncio.run(main())Run Background Tasks with asyncio.create_task in Python
Create background tasks in an asyncio event loop with asyncio.create_task and run them concurrently using asyncio.gather.
import asyncio
import time
async def background_worker(name, duration):
"""Simulates a long-running background task."""
print(f"{name} started at t={time.monotonic():.1f}")
await asyncio.sleep(duration)
print(f"{name} finished at t={time.monotonic():.1f}")
async def main():
print(f"Main starting …Using a Python Generator Instead of a List to Save Memory
Compare a list approach with a generator to stream values lazily, avoiding memory-heavy storage of large sequences.
def fibonacci_generator(limit):
a, b = 0, 1
count = 0
while count < limit:
yield a
a, b = b, a + b
count += 1
def sum_first_n(generator, n):
total = 0
for i, value in enumerate(generator):
if i >= n:
break
total += value
return total
if __…asyncio sleep cooperative scheduling demo in Python
This demo shows how asyncio.sleep yields control between concurrent tasks, letting multiple workers interleave their ticks.
import asyncio
async def worker(name, delay):
for i in range(3):
print(f"{name}: tick {i}")
await asyncio.sleep(delay)
return f"{name} done"
async def main():
tasks = [
asyncio.create_task(worker("A", 0.1)),
asyncio.create_task(worker("B", 0.2)),
asyncio.create_tas…Fix and Test a Regression Bug in Python with Unit Tests
This code implements a circle area function that raises ValueError for negative radii, then runs basic tests and a regression check for that edge case.
import math
def calculate_area(radius):
"""Calculate the area of a circle given its radius."""
if radius < 0:
raise ValueError("Radius cannot be negative")
return math.pi * radius ** 2
def main():
test_cases = [0, 1, 2.5, 5, 10]
print("Circle Area Calculator")
print("-" * 30)
…How to Compare Floats in pytest with approx
Uses pytest.approx to compare floating-point numbers with tolerance, avoiding precision issues.
import pytest
def test_float_addition():
result = 0.1 + 0.2
expected = 0.3
assert result == pytest.approx(expected)How to Group Data by Key in Python with Type Hints
Group a list of dictionaries by a specified key using a typed helper function and print a summary of each group.
from typing import Any, Dict, List, TypeVar, Union
T = TypeVar("T")
def group_by(data: List[Dict[str, Any]], key: str) -> Dict[Any, List[Dict[str, Any]]]:
"""Group a list of dictionaries by a given key."""
grouped: Dict[Any, List[Dict[str, Any]]] = {}
for item in data:
value = item.get(key)
…How to Use Literal Type Hints in Python
Use typing.Literal to restrict a function parameter to specific allowed string values and get static type checking.
from typing import Literal
def get_status_message(status: Literal["active", "inactive", "pending"]) -> str:
"""Return a message based on the status value."""
if status == "active":
return "Account is active"
elif status == "inactive":
return "Account is inactive"
else:
return "…How to Use Union Type Hints in Python
This code demonstrates how to use Union type hints to specify that a parameter can accept multiple types (int, float, str) and handle them accordingly.
from typing import Union
def process_value(value: Union[int, float, str]) -> str:
if isinstance(value, (int, float)):
return f"Number: {value * 2}"
return f"String: {value.upper()}"
if __name__ == "__main__":
print(process_value(10))
print(process_value(3.14))
print(process_value("hello"))How to Use mock.assert_called_with in Python
Verify that a MagicMock received a call with specific positional and keyword arguments using assert_called_with in unittest.
import unittest
from unittest.mock import MagicMock
class TestMockAssertions(unittest.TestCase):
def test_assert_called_with(self):
# Create a mock object
mock = MagicMock()
# Call the mock with specific arguments
mock.send_email("alice@example.com", subject="Greetings", body="Hel…How to use unittest mock side_effect with a sequence in Python
Demonstrates using Mock.side_effect with a list to return different values per call and raise an exception at a specific call in unittest.
import unittest
from unittest.mock import Mock
class TestMockSideEffectSequence(unittest.TestCase):
def test_side_effect_sequence(self):
mock = Mock()
mock.side_effect = [1, 2, 3, Exception("boom")]
self.assertEqual(mock(), 1)
self.assertEqual(mock(), 2)
self.asser…How to Build an Append-Only Event Store in Python
Implement a simple append-only event store class that stores events in a list and supports retrieval by index range.
class EventStore:
def __init__(self):
self._events = []
def append(self, event):
"""Append an event to the store."""
self._events.append(event)
def get_events(self, start=0, end=None):
"""Return events from start index to end (exclusive)."""
return self._events[sta…Round Robin Load Balancer in Python
This code simulates round robin load balancing by distributing a list of requests evenly across a list of servers.
def round_robin_servers(requests: list[str], servers: list[str]) -> dict[str, list[str]]:
assignments = {server: [] for server in servers}
for idx, request in enumerate(requests):
server = servers[idx % len(servers)]
assignments[server].append(request)
return assignments
if __name__ == "_…Generate an OpenAPI Spec from Mock Routes in Python
This Python script generates an OpenAPI 3.0 specification from a simple mock routes dictionary, mapping each HTTP method to response examples.
import json
from pathlib import Path
def generate_openapi_spec(routes: dict, title: str = "Mock API", version: str = "1.0.0") -> dict:
paths = {}
for route, methods in routes.items():
path_item = {}
for method, response_data in methods.items():
method = method.lower()
…How to Add a Correlation ID Tracing Header in Python
A mock middleware generates or preserves a correlation ID header and logs structured JSON messages with it for API request tracing.
import uuid
import json
from dataclasses import dataclass, field
from typing import Optional
@dataclass
class Request:
headers: dict = field(default_factory=dict)
def get(self, key, default=None):
return self.headers.get(key, default)
class CorrelationIdMiddleware:
def __init__(self, header_name…How to Build a WebSocket Echo Server in Python with asyncio
Create a simple WebSocket echo server using the websockets library and asyncio to handle concurrent connections.
import asyncio
import websockets
async def echo(websocket):
async for message in websocket:
await websocket.send(f"Echo: {message}")
async def main():
async with websockets.serve(echo, "localhost", 8765):
print("WebSocket server started on ws://localhost:8765")
await asyncio.Future() …How to Implement Pagination with Offset and Limit in Python
A mock API pagination pattern that parses page and per_page query parameters, computes offset and limit, and slices a list of items for a specific page.
def paginate(items, page, per_page):
offset = (page - 1) * per_page
return items[offset:offset + per_page]
def parse_query_params(query_string):
params = {}
if query_string:
for pair in query_string.split("&"):
key, value = pair.split("=")
params[key] = value
page …How to Propagate X-Request-ID in Python
Generate a unique request ID when one is missing and pass it through API calls for distributed tracing.
import uuid
def generate_request_id() -> str:
"""Generate a unique request ID similar to X-Request-ID header."""
return str(uuid.uuid4())
def propagate_request_id(request_id: str | None) -> str:
"""Return the request ID for propagation, generating one if missing."""
if request_id:
return re…Browse by section
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