EC
StopAsyncIteration
PythonINFOCommonRuntime ErrorHIGH confidence

Async iterator exhausted

Production Risk

Not a real error in async for loops; only visible when manually calling __anext__().

What this means

Raised by __anext__() to signal that an async iterator has no more items. The async for loop catches this automatically; you only see it if calling __anext__() directly.

Why it happens
  1. 1Calling __anext__() on an exhausted async iterator directly (outside async for)
  2. 2Custom async generator raises StopAsyncIteration prematurely
How to reproduce

Calling __anext__() directly on an exhausted async iterator.

trigger — this will error
trigger — this will error
import asyncio

async def main():
    async def agen():
        yield 1

    gen = agen()
    await gen.__anext__()  # Gets 1
    await gen.__anext__()  # Raises StopAsyncIteration

asyncio.run(main())

expected output

StopAsyncIteration

Fix

Use async for instead of __anext__() directly

WHEN Iterating over async generators

Use async for instead of __anext__() directly
async def main():
    async for item in my_async_generator():
        process(item)
    # StopAsyncIteration is caught automatically

Why this works

async for handles StopAsyncIteration internally; only call __anext__() directly if you need manual control.

Code examples
Triggerpython
import asyncio
async def main():
    async def agen():
        yield 1
    g = agen()
    await g.__anext__()
    await g.__anext__()  # StopAsyncIteration
asyncio.run(main())
Handle with try/exceptpython
try:
    val = await gen.__anext__()
except StopAsyncIteration:
    val = None  # exhausted
Avoid with async forpython
async for item in my_async_gen():
    process(item)
# StopAsyncIteration handled automatically
Same error in other languages
async iterator done flagin javascript→
Sources
Official documentation ↗

Python Docs — Built-in Exceptions

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