Reference library

Python Code Samples

Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.

4 matches
Concurrency & performance medium

Limit Concurrency with asyncio.Semaphore in Python

Use asyncio.Semaphore to cap how many async tasks run at once, throttling a batch of coroutines to a set concurrency limit.

asyncio concurrency semaphore
Python 
import asyncio
import random


async def fetch_data(i: int, semaphore: asyncio.Semaphore) -> str:
    async with semaphore:
        print(f"Task {i} starts")
        await asyncio.sleep(random.uniform(0.1, 0.5))
        print(f"Task {i} finishes")
        return f"Result {i}"


async def main() -> None:
    semaphore …
12 0 Open
System design patterns medium

How to Limit Concurrent Requests with a Semaphore in Python

Use threading.Semaphore with a ThreadPoolExecutor to cap how many worker threads run simultaneously, preventing resource overload.

concurrency semaphore threading
Python 
import threading
import time
from concurrent.futures import ThreadPoolExecutor

def worker(name, semaphore, results):
    with semaphore:
        results.append(f"start {name}")
        time.sleep(0.5)  # simulate async work
        results.append(f"done {name}")

def main():
    sem = threading.Semaphore(2)  # max 2 …
13 0 Open
Reliability & rate limiting medium

How to Implement a Bulkhead Pattern with Threading in Python

Implement a bulkhead pattern in Python that isolates concurrent tasks with a bounded semaphore, limiting active workers to prevent resource exhaustion.

bulkhead threading semaphore
Python 
import threading
import time
import random


class Bulkhead:
    def __init__(self, workers: int):
        self._semaphore = threading.BoundedSemaphore(workers)
        self._lock = threading.Lock()
        self._active = 0

    def run(self, task):
        with self._semaphore:
            with self._lock:
          …
13 0 Open
Microservices patterns medium

Bulkhead Thread Pool per Service Mock in Python

Simulates a bulkhead pattern with per-service thread pools and semaphore-based rejection to isolate failures between dependent services.

bulkhead threadpool semaphore
Python 
import threading
import time
import random
from concurrent.futures import ThreadPoolExecutor

class ServiceBulkhead:
    def __init__(self, name, max_threads, max_queue):
        self.name = name
        self.executor = ThreadPoolExecutor(max_workers=max_threads)
        self.semaphore = threading.Semaphore(max_thread…
11 0 Open

Browse by section

Each section groups closely related Python snippets.

Guide: free Python code samples library

Copy-ready Python snippets for learners and developers

PythonSkillset code samples are short, focused examples organised by topic and difficulty. Every snippet is server-rendered HTML — readable by search engines and easy to copy. Open any sample, read the notes, copy the code, then press Try in editor to run it in the browser with Pyodide.

How to use this library

  1. Pick a topic section — strings, lists, files, functions, and more
  2. Open a sample, read How it works, and copy the code block
  3. Run it in the IDE, tweak values, then take a related quiz or tutorial lesson

Samples vs tutorials and challenges

Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.

Related coding tools

Free online Python IDE Write and run Python in your browser — no install. Free Python code formatter Format with autopep8 — side-by-side PEP 8 cleanup.