What is a coroutine object in python

What is a coroutine object?

• A coroutine is a special kind of function that can pause and resume its execution, allowing asynchronous programming.
• When you call an async function, it doesn’t run immediately like a regular function.
• Instead, it returns a coroutine object — essentially a “promise” that it will run when awaited.

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Coroutine object in practice

async def say_hello():
    print("Hello!")
    return "Done"

result = say_hello()  # This returns a coroutine object, it does NOT execute yet
print(result)         # <coroutine object say_hello at 0x...>

# To actually run the coroutine and get the result, you need to await it:
output = await say_hello()  # Now it runs, prints "Hello!" and returns "Done"
print(output)               # "Done"

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Why does this matter?

• Coroutine objects represent tasks that haven’t run yet.
• You must await them inside an async function to actually execute the code and get the result.
• If you don’t await and just return the coroutine, it’s like returning a “recipe” instead of the “finished dish.”

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In your FastAPI app

• Your repository functions are async (return coroutine objects).
• If you return the coroutine itself (without await), FastAPI tries to serialize the coroutine object, which causes errors.
• You must await those async calls so FastAPI gets the actual data to send in the response.

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Summary:

Term	Meaning
coroutine function	A function defined with async def
coroutine object	The result of calling a coroutine function — a "lazy" task not yet run
await	The keyword that runs the coroutine and gets its result