cached-hub

Load HuggingFace models and datasets from a shared local cache, fall back to the Hub, and pre-populate that cache from a declarative list of what a course needs.

Why

In a classroom, every student pulling gpt2, SmolLM2 and imdb from the Hub at the same minute is slow, fragile, and sometimes impossible (no home directory quota, shaky proxy, offline lab). The usual answer is a shared read-only directory pre-filled by the instructor. cached-hub makes that directory a first-class thing:

• notebook code calls load_hf_model("gpt2") and gets the cached copy when it exists, the Hub otherwise, with a one-line note saying which;
• the instructor declares the resources once, and cached-hub download fills the cache (each shared resource once, optional ones on demand);
• an enforce mode turns any cache miss into an error, so you can check that every notebook runs fully from the cache before the session.

The package has no required dependency: transformers, datasets, pyterrier and datamaestro are imported only by the functions that use them. It was extracted from the Sorbonne Master MIND master-mind tool so that a course only needs this package (plus jupytext-notebook-helper for building notebooks).

Install

pip install cached-hub            # loaders only (bring your own transformers/datasets)
pip install "cached-hub[hf]"      # + transformers, datasets

Supported libraries

The loaders differ from their equivalents in one way only: with CACHED_HUB_PATH set, they first look for the resource in the cache layout above, log where it came from, and on a miss forward to the equivalent call with cache_dir=$CACHED_HUB_PATH/huggingface added (unless you passed one), or raise CacheMissError in enforce mode. PyTerrier and datamaestro manage their own caches, so there is no loader for them: cached-hub only declares them as resources so that cached-hub download fetches everything a course needs in one go, and you keep calling those libraries as usual.

In notebooks

from cached_hub import load_hf_model, load_hf_tokenizer, load_hf_dataset, HFModel
from transformers import AutoModelForCausalLM

tokenizer = load_hf_tokenizer("HuggingFaceTB/SmolLM2-1.7B-Instruct")
model = load_hf_model("HuggingFaceTB/SmolLM2-1.7B-Instruct", AutoModelForCausalLM, device_map="auto")
train = load_hf_dataset("imdb", split="train")
sst2 = load_hf_dataset("glue", name="sst2")          # DatasetDict of the cached splits

hf = HFModel("gpt2")            # lazy: nothing is loaded yet
hf.tokenizer, hf.model          # AutoTokenizer / AutoModel, loaded on first access

Each loader checks the local cache first, then falls back to the Hub with a warning. Extra keyword arguments go to from_pretrained / load_dataset.

Configuration

Layout under the root (org/name becomes org-name):

$CACHED_HUB_PATH/huggingface/models/<id>/                 model.save_pretrained()
$CACHED_HUB_PATH/huggingface/tokenizers/<id>/
$CACHED_HUB_PATH/huggingface/processors/<id>/
$CACHED_HUB_PATH/huggingface/datasets/<id>[-<name>]/<split>/   dataset.save_to_disk()
$CACHED_HUB_PATH/huggingface/                             HF cache_dir used for fallbacks

A directory is used only when it contains the marker .downloaded.ok, written after a successful download, so a half-copied model is never picked up.

Without CACHED_HUB_PATH, cached-hub adds no caching of its own. load_hf_model("gpt2", cls, **kw) is then exactly cls.from_pretrained("gpt2", **kw), and load_hf_dataset(...) exactly datasets.load_dataset(...): the usual HuggingFace cache (~/.cache/huggingface, HF_HOME) applies as it always does, and cached-hub download merely warms it. Notebooks can therefore import from cached_hub unconditionally and run unchanged on a laptop or on Colab; only the classroom machines set the variable.

Declaring and downloading resources

A course lists what it needs as {section: [resources]}:

# mycourse/resources.py
from cached_hub import (
    make_hf_model_resource, make_hf_tokenizer_resource, make_hf_processor_resource,
    make_hf_dataset_resource, make_pyterrier_dataset_resource, make_datamaestro_resource,
)

RESOURCES = {
    "practical1": [
        make_hf_model_resource("gpt2", model_class="GPT2LMHeadModel"),
        make_hf_tokenizer_resource("gpt2", tokenizer_class="GPT2Tokenizer"),
        make_hf_dataset_resource("imdb", ["train", "test"]),
    ],
    "practical2": [
        make_hf_model_resource("Qwen/Qwen2.5-7B-Instruct", model_class="AutoModelForCausalLM", optional=True),
        make_pyterrier_dataset_resource("irds:lotte/technology/dev/search", "LoTTE technology"),
    ],
}

then, on the machine that hosts the cache:

export CACHED_HUB_PATH=/shared/cache
cached-hub info
cached-hub list     --from mycourse.resources:RESOURCES
cached-hub download --from mycourse.resources:RESOURCES               # everything but optional
cached-hub download --from mycourse.resources:RESOURCES --section practical2 --optional
cached-hub download --from mycourse.resources:RESOURCES --key gpt2

--from MODULE:ATTR imports MODULE and reads ATTR from it: a {section: [resources]} mapping, or a zero-argument callable returning one (dotted attributes such as plugin.Course.resources are followed). RESOURCES above is only a naming convention. The option can be repeated. Resources are identified by (type, key), so a model shared by several practicals is downloaded once. HF_HUB_OFFLINE is lifted for the duration of a download.

The same helpers are available from Python (download_resources, select_resources, format_resources, merge_resources), and any object with resource_type, key, description, optional and download() is a valid resource (FunctionalResource wraps a plain function).

Keeping the declaration honest

The declaration is written by hand, so it drifts: a notebook gains a model, an old one stops being loaded, and the classroom cache is wrong on the morning it matters. scan reads the loader calls back out of the sources, and check compares them with the declaration:

cached-hub scan  sources/                      # what the sources load
cached-hub scan  sources/ --emit practical2    # a declaration skeleton to fill in
cached-hub check sources/ --declaration mycourse/resources.py   # exit 1 on drift

A section is a source file name (sources/02-generation.py -> 02-generation), which is what --section takes. Both commands accept files or directories (a directory contributes its top-level *.py, _-prefixed excluded), and --search-path DIR lets an imported helper module be scanned as part of the file that imports it — for course code split between a notebook and a library.

What the scan understands: load_hf_model / load_hf_tokenizer / load_hf_processor / load_hf_dataset / HFModel / pt.get_dataset / prepare_dataset, with module-level string constants resolved (MODEL = "gpt2" … load_hf_model(MODEL, …)). A constant rebound under a guard — if test_mode: by default, --guard NAME for another one — becomes an optional=True resource, since a small stand-in used while testing has no business filling a classroom cache. Plain load_dataset and Class.from_pretrained calls are reported as bypasses: they do not go through the cache, so check never asks for them to be declared.

check reports as errors anything loaded but not declared, or declared but never loaded, and as warnings a class or optional mismatch. Descriptions and dataset splits are left alone: code that loads every split says nothing about their names.

In a Makefile:

check-resources:
	cached-hub check sources/ --declaration mycourse/resources.py

Checking a cache before class

CACHED_HUB_PATH=/shared/cache CACHED_HUB_ENFORCE=1 python practical1.py

fails at the first resource that would have gone to the Hub.