Working with async and await in Python

Python introduced the async and await keywords to support asynchronous programming. These keywords help developers write non-blocking code that can perform multiple tasks concurrently, making it especially useful for I/O-bound operations such as network requests, file handling, and database access.

What is async in Python?

The async keyword is used to define a coroutine, which is a special type of function that can pause execution and allow other tasks to run. Coroutines are the building blocks of asynchronous programming in Python.

What is await in Python?

The await keyword is used to pause the execution of a coroutine until the awaited task is completed. It can only be used inside a coroutine defined with async def.

Basic Example of async and await

This example demonstrates how to define and run a simple coroutine using async and await.

    import asyncio

    async def greet():
        print("Hello, World!")
        await asyncio.sleep(1)
        print("Goodbye, World!")

    # Running the coroutine
    asyncio.run(greet())
        

Output:

    Hello, World!
    Goodbye, World!
        

Using await to Call Other Coroutines

You can use await to call other coroutines, allowing them to pause and resume execution.

    import asyncio

    async def fetch_data():
        print("Fetching data...")
        await asyncio.sleep(2)
        print("Data fetched!")

    async def process_data():
        print("Processing data...")
        await asyncio.sleep(1)
        print("Data processed!")

    async def main():
        await fetch_data()
        await process_data()

    asyncio.run(main())
        

Output:

    Fetching data...
    Data fetched!
    Processing data...
    Data processed!
        

Running Coroutines Concurrently

The asyncio.gather function allows you to run multiple coroutines concurrently.

    import asyncio

    async def task_one():
        print("Task one starting")
        await asyncio.sleep(2)
        print("Task one completed")

    async def task_two():
        print("Task two starting")
        await asyncio.sleep(1)
        print("Task two completed")

    async def main():
        await asyncio.gather(task_one(), task_two())

    asyncio.run(main())
        

Output:

    Task one starting
    Task two starting
    Task two completed
    Task one completed
        

Creating and Managing Tasks with asyncio.create_task

You can create and manage tasks independently using asyncio.create_task.

    import asyncio

    async def print_numbers():
        for i in range(5):
            print(f"Number: {i}")
            await asyncio.sleep(1)

    async def main():
        task = asyncio.create_task(print_numbers())
        print("Task created!")
        await task
        print("Task completed")

    asyncio.run(main())
        

Output:

    Task created!
    Number: 0
    Number: 1
    Number: 2
    Number: 3
    Number: 4
    Task completed
        

Using async and await with Asynchronous Generators

Asynchronous generators allow you to yield values asynchronously using async def and yield.

    import asyncio

    async def async_generator():
        for i in range(3):
            await asyncio.sleep(1)
            yield i

    async def main():
        async for value in async_generator():
            print(f"Generated: {value}")

    asyncio.run(main())
        

Output:

    Generated: 0
    Generated: 1
    Generated: 2
        

Advantages of Using async and await

• Efficient handling of I/O-bound tasks.
• Allows for concurrent execution of multiple tasks.
• Provides a clear and readable syntax for asynchronous programming.

Limitations

• Not suitable for CPU-bound tasks.
• Requires understanding of asynchronous programming concepts.
• Debugging can be more challenging than synchronous code.

Conclusion

The async and await keywords in Python simplify asynchronous programming, making it easier to write efficient and non-blocking code. By mastering these concepts and the tools provided by the asyncio module, developers can handle I/O-bound tasks more effectively.