对于字典中的循环，pytorch

Question

大家好，我有一个问题，变量 "image_datasets" 有一个 for 循环 for x in ['train', 'val']。以前没见过在dict中实现for循环的。

data_transforms = {
'train': transforms.Compose([
    transforms.RandomResizedCrop(224),
    transforms.RandomHorizontalFlip(),
    transforms.ToTensor(),
    transforms.Normalize(mean, std)
]),
'val': transforms.Compose([
    transforms.Resize(256),
    transforms.CenterCrop(224),
    transforms.ToTensor(),
    transforms.Normalize(mean, std)
]),
}

data_dir = 'data/hymenoptera_data'
image_datasets = {x: datasets.ImageFolder(os.path.join(data_dir, x),
                                          data_transforms[x])
                  for x in ['train', 'val']}
dataloaders = {x: torch.utils.data.DataLoader(image_datasets[x], batch_size=4,
                                             shuffle=True, num_workers=0)
              for x in ['train', 'val']}

dataset_sizes = {x: len(image_datasets[x]) for x in ['train', 'val']}
class_names = image_datasets['train'].classes

Answer 1

它被称为dict comprehension and there's also list comprehensions： https://book.pythontips.com/en/latest/comprehensions.html

它们的功能基本上与您预期的一样：

Do X with x for x in List

然后将结果用作字典或列表等的输入。

Answer 2

这称为 dictionary comprehension，它正在遍历列表。

代码

dataloaders = {
    x: torch.utils.data.DataLoader(
        image_datasets[x],
        batch_size=4,
        shuffle=True,
        num_workers=0
    )
    for x in ['train', 'val']
}

相当于

dataloaders = {
    'train': torch.utils.data.DataLoader(
        image_datasets['train'],
        batch_size=4,
        shuffle=True,
        num_workers=0
    ),
    'val': torch.utils.data.DataLoader(
        image_datasets['val'],
        batch_size=4,
        shuffle=True,
        num_workers=0
    )
}

对于字典中的循环，pytorch

For loops in a dictionary, pytorch

python

pytorch