Passing Dicts using Pointers in Python HuggingFace

Question

AFAIK, in Python objects are passed by reference, then why do HuggingFace keeps using pointers to pass objects? Example snippet below taken from the tutorial at this link: https://huggingface.co/learn/nlp-course/chapter3/4?fw=pt

raw_inputs = [
    "I've been waiting for a HuggingFace course my whole life.",
    "I hate this so much!",
]
inputs = tokenizer(raw_inputs, padding=True, truncation=True, return_tensors="pt")
print(inputs)

from transformers import AutoModel

checkpoint = "distilbert-base-uncased-finetuned-sst-2-english"
model = AutoModel.from_pretrained(checkpoint)

outputs = model(**batch)  #  <-- What does this even mean? 
print(outputs.loss, outputs.logits.shape)

Corrected URL: https://huggingface.co/learn/nlp-course/chapter2/2?fw=pt SO not letting me edit url in the original post — The Wanderer, Jun 17 '23 at 03:19
Python does not use the same syntax as C. `**` is dictionary unpacking in Python, not pointer dereferencing. The elements of `batch` become keyword arguments to `model` with that call. — Carcigenicate, Jun 17 '23 at 03:20
see: https://www.geeksforgeeks.org/packing-and-unpacking-arguments-in-python/ — ocean moist, Jun 17 '23 at 03:20
Python does *not have pointers*, and it never uses call by reference as an evaluation strategy. — juanpa.arrivillaga, Jun 17 '23 at 03:27
Python and C are two different languages, and `*` has nothing to do with pointers in Python — juanpa.arrivillaga, Jun 17 '23 at 03:28

score 2 · Accepted Answer · answered Jun 17 '23 at 03:23

2

func(**kwargs) is passing dictionary kwargs as keyword (non-positional) arguments to func.

If func is defined as such:

def func(arg1, arg2, arg3):
    pass

And dict kwargs is such:

kwargs = {
    "arg1": value1,
    "arg2": value2,
    "arg3": value3,
}

Then calling func(**kwargs) is equivalent to calling func(arg1=value1, arg2=value2, arg3=value3).

It has nothing to do with pointers. Python does not have pointers.

answered Jun 17 '23 at 03:23

Bolong

164
2

Yes, while the Python language does not have the notion of pointers outside of its C API, the arguments passed to functions are still done via pointers to `PyObject`s uder the hood. Python *does* use pointers, but they're hidden from view. Python uses pointers extensively, but they're hidden from normal use. – Carcigenicate Jun 17 '23 at 03:30

Passing Dicts using Pointers in Python HuggingFace

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