nbs/examples/dataloader_spawn.py

#!/usr/bin/env python
# coding: utf-8

from fastai.vision.all import *

def get_data(url, presize, resize):
    path = untar_data(url)
    #print(Normalize.from_stats(*imagenet_stats))
    return DataBlock(
        blocks=(ImageBlock, CategoryBlock), get_items=get_image_files, 
        splitter=GrandparentSplitter(valid_name='val'),
        get_y=parent_label, item_tfms=Resize(presize),
        batch_tfms=aug_transforms(min_scale=0.5, size=resize),
    ).dataloaders(path, bs=128)

def block(ni, nf): return ConvLayer(ni, nf, stride=2)
def get_model():
    return nn.Sequential(
        block(3, 16),
        block(16, 32),
        block(32, 64),
        block(64, 128),
        block(128, 256),
        nn.AdaptiveAvgPool2d(1),
        Flatten(),
        nn.Linear(256, dls.c))

def get_learner(dls, m):
    return Learner(dls, m, loss_func=nn.CrossEntropyLoss(), metrics=accuracy
                  )

if __name__ == "__main__":
    multiprocessing.set_start_method('spawn')
    dls = get_data(URLs.IMAGENETTE_160, 160, 128)
    resnet_model = get_model()
    learn = get_learner(dls, resnet_model)
    learn.lr_find()