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Fixing Python ValueError: Expected Coroutine, Got Function

Last updated: December 31, 2023

Understanding the Error

When programming with Python, a ValueError suggesting an expected coroutine but received a function typically occurs within an asynchronous context. This error indicates that an asynchronous function (defined using async def) is expected where a coroutine object is required, but a regular function was provided instead. It generally happens when you invoke an asynchronous function without the await keyword. The await keyword is essential in telling Python to wait for the completion of the asynchronous operation.

Addressing the Error

To fix this error, first, ensure that the function intended to be executed asynchronously is defined using async def instead of the regular def. Then, when calling this asynchronous function, use the await keyword before the function call. This allows the event loop to manage the asynchronous call appropriately.

Working Example

The following code illustrates the correct implementation of an asynchronous function and its invocation:

import asyncio

async def do_something():
    print('Doing something asynchronously')
    await asyncio.sleep(1)  # Simulate an I/O operation

async def main():
    await do_something()

if __name__ == '__main__':
    asyncio.run(main())

Alternative Solutions

If the function in question is not designed to be asynchronous but is required in an async context, one of the solutions is to run it in a separate executor using loop.run_in_executor. Another option is refactoring the synchronous function as an asynchronous one if possible.

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Series: Common Errors in Python and How to Fix Them

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