Python RuntimeWarning: Coroutine Was Never Awaited

Python’s asyncio module provides a powerful framework for writing asynchronous code using coroutines. While asyncio simplifies the handling of concurrent operations, developers may encounter the “RuntimeWarning: Coroutine Was Never Awaited” message, which indicates an issue with how coroutines are being used.

What is “Runtimewarning: Coroutine Was Never Awaited”?

The warning “RuntimeWarning: Coroutine Was Never Awaited” typically arises when a coroutine function is defined but not awaited properly. In Python, a coroutine is a special type of function that can be paused and resumed, allowing for asynchronous execution. When you define a coroutine, you must use the await keyword to execute it. Failure to do so can result in a runtime warning.

Syntax:

Runtimewarning: Coroutine Was Never Awaited

Why does Python RuntimeWarning: Coroutine Was Never Awaited Occur?

Below, are the reasons of occurring “Runtimewarning: Coroutine Was Never Awaited” in Python:

• Missing Await Keyword
• Incorrect Usage of Coroutine
• Nested Coroutines

Missing Wait Keyword

The most straightforward cause of this warning is forgetting to use the await keyword before calling a coroutine function and this lead to this warning.

Python3

async def example_coroutine():
    print("This is a coroutine")

#Missing await keyword
example_coroutine()

Output:

Solution.py:5: RuntimeWarning: coroutine 'example_coroutine' was never awaited
  example_coroutine()
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

Incorrect Usage of Coroutine

Another reason for the warning may be using a coroutine in a synchronous context where the asynchronous features are not supported.

Python3

async def example_coroutine():
    print("This is a coroutine")

result = example_coroutine()

Output:

sys:1: RuntimeWarning: coroutine 'example_coroutine' was never awaited

Nested Coroutines

If you have nested coroutine calls make sure that each coroutine is properly awaited at its respective level otherwise it will raise the error.

Python3

async def outer_coroutine():
    await inner_coroutine()

async def inner_coroutine():
    print("Nested coroutine")

outer_coroutine()

Output:

Solution.py:7: RuntimeWarning: coroutine 'outer_coroutine' was never awaited
  outer_coroutine()
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

Solution for Python RuntimeWarning: Coroutine Was Never Awaited

Below, are the approaches to solve “Runtimewarning: Coroutine Was Never Awaited”.

• Add Await Keyword
• Correct Usage of Coroutine
• Nested Coroutines

Add Await Keyword

Add the “await” keyword in your code to avoid the error.

Python3

async def example_coroutine():
    print("This is a coroutine")

#Added the await keyword
await example_coroutine()

Output:

This is a coroutine

Correct Usage of Coroutine

If you are working within an asynchronous context such as an async def function make sure that all coroutines are called within this context.

Python3

async def main():
    await example_coroutine()

asyncio.run(main())

Output:

This is a coroutine

Nested Coroutines

If you have nested coroutines make sure that each coroutine is properly awaited at its respective level. Use “await” keyword according to the level.

Python3

async def outer_coroutine():
    await inner_coroutine()

async def inner_coroutine():
    print("Nested coroutine")

await outer_coroutine()

Output:

Nested coroutine

Conclusion

In conclusion , Asynchronous programming in Python using coroutines can be powerful, but it requires careful attention to detail. The “RuntimeWarning: Coroutine Was Never Awaited” message serves as a reminder to properly handle coroutine functions. By understanding the common causes and implementing the suggested fixes, you can ensure your asynchronous code runs smoothly without triggering this warning.