DEV Community

Cover image for Python Multithreading: Unlocking Concurrency for Better Performance
Wallace Espindola
Wallace Espindola

Posted on

Python Multithreading: Unlocking Concurrency for Better Performance

Hey, let's dive into the world of Python multithreading! Whether you're an intermediate or advanced developer, or maybe even coming from another programming language, mastering this will boost your skills and your applications' performance. Ready to tackle it? Let's go!

Why Multithreading?

Multithreading can seem daunting, but it's a game-changer for performing multiple operations at once, especially when dealing with I/O-bound or high-latency operations. Think of it as hiring more workers for your shop when it gets busy. Each worker handles a different customer simultaneously, speeding up service. That's what threads do for your programs.

Setting Up Your Workshop – The Basics

First, let's set up our environment. Python provides a built-in module for threading called threading. Here’s how you get started:

import threading

def do_something():
    print("Look, I'm running in a thread!")

# Create a thread
thread = threading.Thread(target=do_something)

# Start the thread

# Wait for the thread to complete

print("All done!")
Enter fullscreen mode Exit fullscreen mode

This basic setup creates and starts a thread that runs a function. The join() method is crucial, as it tells Python to wait for the thread to complete before moving on.

Best Practices for Healthy Threading

1. Keep the GIL in mind: Python’s Global Interpreter Lock (GIL) allows only one thread to execute at a time in a single process, which can be a bottleneck. But don’t worry! This mainly affects CPU-bound tasks. For I/O-bound tasks, threading can still be very beneficial.

2. Use ThreadPoolExecutor: This is a fantastic tool from the concurrent.futures module. It simplifies managing a pool of threads and handling tasks. Here’s how you can use it:

from concurrent.futures import ThreadPoolExecutor

def task(n):
    print(f"Processing {n}")

with ThreadPoolExecutor(max_workers=3) as executor:
    results =, range(1, 4))
Enter fullscreen mode Exit fullscreen mode

This example creates a pool of three threads, each processing a part of a range of numbers. Using ThreadPoolExecutor not only simplifies thread management but also handles task distribution and collection elegantly.

3. Don’t share state if possible: Sharing data between threads can lead to data corruption and other nasty bugs if not handled properly. If you must share data, use locks:

from threading import Lock

lock = Lock()
shared_resource = []

def safely_add(item):
    with lock:

threads = [
    threading.Thread(target=safely_add, args=(i,)) for i in range(10)

for thread in threads:

for thread in threads:

Enter fullscreen mode Exit fullscreen mode

Each thread in this example safely adds an item to a shared list, thanks to the lock that ensures only one thread modifies the list at a time.

When Not to Use Multithreading

Gotcha! While multithreading is powerful, it’s not a silver bullet. For CPU-bound tasks that require heavy computation and little I/O, consider using multiprocessing or asynchronous programming (like asyncio) instead. These tools can bypass the GIL and truly run code in parallel, maximizing CPU usage.

Debugging Multithreaded Applications

Yes, it can be tricky! Here are a couple of quick tips:

- Logging is your friend: Use Python’s logging module to help track down what each thread is doing.

- Use debuggers that understand threads: Tools like IntelliJ, PyCharm and VS Code have debuggers that can handle threading well.

Wrapping Up with a Real-World Example

Imagine you're building a web scraper that downloads content from multiple URLs. Multithreading can significantly speed up this process since network requests are I/O-bound. Here’s a sketch of how you might set this up:

from concurrent.futures import ThreadPoolExecutor
import requests

def fetch(url):
    response = requests.get(url)
    return response.text

urls = ["", "", ""]

with ThreadPoolExecutor(max_workers=5) as executor:
    results = list(, urls))

print("Fetched the content of all URLs!")
Enter fullscreen mode Exit fullscreen mode

This example fetches data from multiple URLs in parallel. Each thread handles downloading the content from one URL, which is typically a slow operation due to network latency.

Keep Learning and Experimenting

Multithreading is a vast topic, and mastering it can take some time. Keep experimenting with different scenarios and tweak your approach as you learn more about Python's capabilities and limitations. Remember, the more you practice, the better you’ll get!

Now, why not try implementing a multithreaded solution in your next project? Dive in, break things, fix them, and learn. Go ahead!

You may check this python-multithreading project I created on GitHub with examples and tests, and also, for other interesting technical discussions and subjects, check my LinkedIn page. Happy coding!

Top comments (1)

mediumrowdy profile image

Thanks for posting this.

It provides a fairly simple explanation with some good examples, and has (finally) prompted me to investigate Python threading a little to update a couple of utilities I have.