processing.py

# function 1
# load image from the given url
response = requests.get(url)
img = Image.open(io.BytesIO(response.content))

# function 2
# load model. This is a time-consuming operation
model = load_model()

# function 3
# returns a pair (x_adv, grad) after each FGSM step.
iterator = iterative_fast_gradient_sign_(
    model,
    preprocess(img),
    epsilon,
    n_steps=n_steps,
    alpha=alpha
)