How to Use asyncio.gather in Python for Concurrent Tasks

Use asyncio.gather to run multiple asynchronous tasks concurrently in Python. It takes multiple awaitable objects and returns their results as a list once all complete.

Syntax

The basic syntax of asyncio.gather is:

asyncio.gather(*tasks, return_exceptions=False)

• *tasks: One or more awaitable objects (like async functions or coroutines).
• return_exceptions: Optional boolean; if True, exceptions are returned as results instead of raising.

This function runs all tasks concurrently and waits for all to finish, returning their results in order.

python

asyncio.gather(*tasks, return_exceptions=False)

Example

This example shows how to run two async functions concurrently using asyncio.gather and get their results together.

python

import asyncio

async def say_after(delay, message):
    await asyncio.sleep(delay)
    return message

async def main():
    task1 = say_after(2, 'hello')
    task2 = say_after(1, 'world')
    results = await asyncio.gather(task1, task2)
    print(results)

asyncio.run(main())

Output

['hello', 'world']

Common Pitfalls

Common mistakes when using asyncio.gather include:

• Not awaiting asyncio.gather itself, which means tasks won't run.
• Passing non-awaitable objects, causing errors.
• Ignoring exceptions raised by tasks, which can stop all tasks unless return_exceptions=True is used.

Here is an example showing the wrong and right way:

python

import asyncio

async def fail():
    raise ValueError('Oops')

async def main_wrong():
    # Missing await - tasks won't run
    asyncio.gather(fail())

async def main_right():
    # Await gather to run tasks and catch exceptions
    results = await asyncio.gather(fail(), return_exceptions=True)
    print(results)

# To test, run asyncio.run(main_right())

Output

[ValueError('Oops')]

Quick Reference

Parameter	Description
*tasks	Multiple awaitable objects to run concurrently
return_exceptions	If True, exceptions are returned as results instead of raised
Returns	A list of results in the order tasks were passed

Key Takeaways

Always await asyncio.gather to run tasks concurrently and get results.

Pass only awaitable objects like async functions or coroutines to asyncio.gather.

Use return_exceptions=True to handle exceptions without stopping all tasks.

Results are returned in the same order as the tasks were passed.

asyncio.gather is useful for running multiple async operations at the same time efficiently.