What is a non-blocking code in Python?

Non-blocking code in Python refers to code that allows the program to continue executing other tasks without waiting for a particular operation to complete.

In other words, non-blocking code enables concurrent or asynchronous execution of multiple tasks without causing the program to be blocked or stalled while waiting for some operation to finish.

Python has a Global Interpreter Lock (GIL) that prevents multiple native threads from executing Python bytecodes simultaneously in a single process.

This means that in some cases, even if you use threads, only one thread can execute Python code at a time.

However, non-blocking behavior can still be achieved using techniques such as asynchronous programming and multiprocessing.

  1. Asynchronous Programming (async/await): Python provides the asyncio module for writing asynchronous code using the async and await keywords. This allows you to write code that can pause at certain points and yield control back to the event loop, enabling other tasks to continue executing. This is especially useful for I/O-bound operations, where waiting for data from external sources like files, networks, or databases can be time-consuming.
  2. Multiprocessing: Python’s multiprocessing module allows you to create multiple processes, each with its own Python interpreter and memory space. This enables true parallel execution of code on multi-core CPUs, bypassing the GIL limitation. Each process can perform its tasks independently and concurrently.

In both of these approaches, the key idea is to structure your code in a way that allows it to execute multiple tasks simultaneously without waiting for each task to complete. This is essential for building responsive applications, handling multiple I/O operations efficiently, and utilizing the full potential of modern hardware.

Here’s a simple example of asynchronous code using asyncio:

import asyncio

async def main():
    await asyncio.sleep(1)


In this example, the await asyncio.sleep(1) line doesn’t block the entire program. Instead, it allows other tasks to run during the sleep period. So, the “End” message is printed after the “Start” message without waiting for the sleep to finish.

Remember that non-blocking code is particularly useful when dealing with I/O-bound operations and parallelism. CPU-bound operations might require a different approach, such as multiprocessing, to fully utilize available resources.

Are Python functions blocking?

Yes, Python functions are generally blocking by default. When you call a function in Python, the program’s execution flow will pause at that point and wait for the function to complete before moving on to the next instruction. This is the standard behavior for most functions in Python and many programming languages.

For example, consider the following code:

def do_work():
    print("Work started")
    # Simulate some time-consuming operation
    for i in range(5):
        print(f"Working... {i}")
    print("Work completed")

print("Before calling do_work()")
print("After calling do_work()")

In this code, the execution will follow these steps:

  1. “Before calling do_work()” will be printed.
  2. The do_work() function will be called, and the program’s execution will be blocked inside the function until the loop completes.
  3. “Work started” and the loop iteration messages will be printed.
  4. “Work completed” will be printed.
  5. “After calling do_work()” will be printed.

During the time the do_work() function is executing, the program is essentially blocked and can’t perform other tasks.

However, there are ways to achieve non-blocking behavior in Python, such as using asynchronous programming with the async and await keywords and utilizing features like the asyncio library. Additionally, if you need true parallelism and want to perform multiple tasks concurrently, you can use the multiprocessing module to create separate processes that can execute in parallel, bypassing the Global Interpreter Lock (GIL) limitation.

Is Python select blocking?

Yes, the select function in Python is a blocking operation.

The select function is used for managing I/O in a non-blocking manner, allowing you to wait for multiple I/O operations on multiple file descriptors or sockets to become ready for reading or writing.

It’s often used in network programming to handle multiple socket connections efficiently without blocking the entire program.

However, while select itself is non-blocking in the sense that it allows you to wait for multiple I/O events without stopping the entire program, when you call the select function, it will block until one of the specified file descriptors or sockets becomes ready for the specified I/O operation (read, write, or error).

This means that the program will wait at the select call until there is an event to handle, potentially causing a delay in other parts of your code.

If you’re looking for a truly non-blocking approach to handling I/O operations, especially in scenarios involving a large number of concurrent connections or tasks, you might consider using asynchronous programming with the asyncio module or other asynchronous libraries.

These approaches allow you to structure your code in a way that can continue executing other tasks while waiting for I/O events without blocking the program’s execution.

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  • Muhammad Nabil

    I am a skilled and experienced Python developer with a huge passion for programming and a keen eye for details. I earned a Bachelor's degree in Computer Engineering in 2019 from the Modern Academy for Engineering and Technology. I am passionate about helping programmers write better Python code, and I am confident that I can make a significant contribution to any team. I am also a creative thinker who can come up with new and innovative ways to improve the efficiency and readability of code. My specialization includes Python, Django, SQL, Apache NiFi, Apache Hadoop, AWS, and Linux (CentOS and Ubuntu). Besides my passion for Python, I am a solo traveler who loves Pink Floyd, online video games, and Italian pizza.

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