Summary
Since Python 3.12, asyncio.as_completed accepts generators that yield tasks.
The tqdm wrapper rejects the same input when total is omitted because it calls len(fs) unconditionally:
Reproduction
import asyncio
from tqdm.asyncio import tqdm_asyncio
async def main():
tasks = (
asyncio.create_task(asyncio.sleep(0, result=value))
for value in range(3)
)
results = []
for future in tqdm_asyncio.as_completed(tasks):
results.append(await future)
print(results)
asyncio.run(main())On Python 3.12.3 Output:
Traceback (most recent call last):
File "/home/test.py", line 17, in <module>
asyncio.run(main())
File "/usr/lib/python3.12/asyncio/runners.py", line 194, in run
return runner.run(main)
^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/asyncio/base_events.py", line 687, in run_until_complete
return future.result()
^^^^^^^^^^^^^^^
File "/home/test.py", line 12, in main
for future in tqdm_asyncio.as_completed(tasks):
File "/home/tqdm/tqdm/asyncio.py", line 67, in as_completed
total = len(fs)
^^^^^^^
TypeError: object of type 'generator' has no len()
Passing the same generator directly to asyncio.as_completed works. A list works with either implementation, and explicitly passing total=3 also avoids the failure.
Environment
Python 3.12.3 (main, Jun 19 2026, 12:46:00) [GCC 13.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tqdm, sys
>>> print(tqdm.__version__, sys.version, sys.platform)
4.70.0 3.12.3 (main, Jun 19 2026, 12:46:00) [GCC 13.3.0] linux
read the known issues
Summary
Since Python 3.12,
asyncio.as_completedaccepts generators that yield tasks.The tqdm wrapper rejects the same input when
totalis omitted because it callslen(fs)unconditionally:Reproduction
On Python 3.12.3 Output:
Passing the same generator directly to
asyncio.as_completedworks. A list works with either implementation, and explicitly passingtotal=3also avoids the failure.Environment