TypeError: object coroutine cant be used in await expression in AsyncIO

Verified FixPython 3.10+Python Native AsyncIOSilo: asyncio

Quick Fix / Solution Rapide

Add parentheses to call the coroutine function: change await fetch_data to await fetch_data().

Root Cause Analysis

This error occurs when Python executes an await expression on an un-called coroutine function reference (await async_function), or conversely attempts to await an object that does not implement the __await__ protocol.

1. Missing Parentheses on Async Function Calls

In Python, an async def my_func(): declaration defines a coroutine function (a function that returns a coroutine object when called). Writing await my_func passes the raw function object to await. Because function objects do not implement __await__, Python raises TypeError: object coroutine can't be used in 'await' expression or TypeError: object function can't be used in 'await' expression.

2. Awaiting Synchronous Helper Functions

Attempting to await a regular def synchronous function that returns a standard primitive (like a string or int) triggers TypeError: object int can't be used in 'await' expression.

3. Double Awaiting a Coroutine Object

Assigning coro = my_func() and calling await coro twice: a coroutine object can only be consumed once.

4. Passing Coroutine Functions into asyncio.gather Without Invoking

Passing asyncio.gather(func1, func2) instead of asyncio.gather(func1(), func2()).

Reproduction Code (MCVE)

Example: Bug Reproduction

import asyncio

async def fetch_user():
    return {'id': 1}

async def main():
    # Bug: missing parentheses await fetch_user instead of await fetch_user()
    await fetch_user

asyncio.run(main())

Solution 1: Invoke Coroutine Function with Parentheses

Add parentheses to execute the function and pass the resulting coroutine object to await.

Example: Recommended Solution

import asyncio

async def fetch_user():
    await asyncio.sleep(0.01)
    return {'id': 1, 'name': 'Alice'}

async def main():
    # Correct: call the coroutine function
    user = await fetch_user()
    print(f'User retrieved: {user}')

asyncio.run(main())

Solution 2: Use asyncio.to_thread for Synchronous Blocking Functions

If the function is synchronous and cannot be awaited directly, run it in a thread pool using asyncio.to_thread().

Example: Alternative Solution

import asyncio
import time

def sync_blocking_task(n):
    time.sleep(0.01)
    return n * 2

async def main():
    # Safely execute synchronous functions in async pipelines
    result = await asyncio.to_thread(sync_blocking_task, 21)
    print(f'Thread result: {result}')

asyncio.run(main())

A common mistake is forgetting await entirely on an async call (e.g. user = fetch_user()). This returns an un-awaited <coroutine object> and causes Python to emit RuntimeWarning: coroutine 'fetch_user' was never awaited. Always pair async function calls with await. Edge cases occur with class methods: ensure @classmethod or @staticmethod decorators precede async def. Contrast this error with TypeError: 'coroutine' object is not subscriptable, which occurs when doing fetch_user()['id'] without await.

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