[FIXED] asyncio.gather with generator expression

Issue

Why doesn't asyncio.gather work with a generator expression?

import asyncio

async def func():
    await asyncio.sleep(2)

# Works
async def call3():
    x = (func() for x in range(3))
    await asyncio.gather(*x)

# Doesn't work
async def call3():
    await asyncio.gather(func() for x in range(3))

# Works
async def call3():
    await asyncio.gather(*[func() for x in range(3)])

asyncio.run(call3())

The second variant gives:

[...]
  File "test.py", line 13, in <genexpr>
    await asyncio.gather(func() for x in range(3))
RuntimeError: Task got bad yield: <coroutine object func at 0x10421dc20>

Is this expected behavior?

Solution

await asyncio.gather(func() for x in range(3))

This doesn't work because this is passing the generator object as argument to gather. gather doesn't expect an iterable, it expects coroutines as individual arguments. Which means you need to unpack the generator.

Answered By - deceze