Скачать или смотреть How to Return a Value from asyncio.run in a Synchronous Function

Discover how to properly return a value from an `asyncio.run` call inside a synchronous function in Python. Learn essential tips and examples for better asynchronous programming!
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This video is based on the question https://stackoverflow.com/q/62228663/ asked by the user 'Ardhi' ( https://stackoverflow.com/u/5912144/ ) and on the answer https://stackoverflow.com/a/62232885/ provided by the user 'Mikhail Gerasimov' ( https://stackoverflow.com/u/1113207/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: Returning None from asyncio.run

When dealing with asynchronous programming in Python, you might find yourself questioning why your function returns None. This scenario often arises when you try to invoke asyncio.run inside a synchronous function and expect it to return a value, but instead, you get a None return. In this guide, we will explore the underlying issue of this behavior and provide a solution that meets your intentions.

The Problem

Here's a simple code snippet that illustrates the issue:

[[See Video to Reveal this Text or Code Snippet]]

In this example, when we call syncFunc(), we would expect it to return the string 'hello', but it instead returns None. Why does this happen?

Why the Function Returns None

The reason behind this behavior is straightforward. In Python, if a function does not explicitly return a value, it defaults to returning None. In our syncFunc, even though we call asyncio.run(testAsync()), we do not use return to send this result back from the function. Consequently, the function ends without returning any value, leading to None being returned when syncFunc() is called.

Solution: Modifying the Function to Return the Value

To remedy this situation and successfully return the desired value, we need to adjust the syncFunc as follows:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Solution

Define Inner Async Function: We maintain the testAsync function, which is defined to return the string 'hello'.

Return from syncFunc: The key change is that we now include return in syncFunc, which sends the result of asyncio.run(testAsync()) back to the caller.

Successful Print: Now, when syncFunc() is called, the result will correctly hold the value 'hello', which will be printed as expected.

Key Takeaways

Always Use Return: If you want a synchronous function that includes an asynchronous call to return a value, ensure that you explicitly return the result of the asynchronous function call.

Understanding Asynchronous Context: Recognizing how asyncio functions work in relation to synchronous code can prevent confusion and lead to cleaner programming patterns.

Conclusion

By following the guidance in this post, you can effectively manage the intricacies of asynchronous programming in Python with the asyncio library. Now, the next time you find yourself in a similar situation, remember to use the return statement to ensure your functions behave as expected!

Whether you’re an aspiring developer looking to sharpen your skills or an experienced programmer refining your techniques, understanding these concepts will help you harness the full power of Python's asynchronous capabilities.