今天在看莫凡的torch教程，cnn案例。封装的函数不一样，所以第一次跑demo的时候需要下载数据集。

但是我发现，可能是由于网站的维护问题，是的数据集下载非常非常缓慢，难以忍受。所以在结合源码以及以前下载的matlab环境下使用的数据集。做了以下处理：

数据集：

另外先在目录下新建mnist文件夹，在mnist文件夹下再建raw和processed文件夹。

自己的电脑只是路径的不一样。此时文件夹中是空的，先将数据集（压缩格式）复制到raw中：

然后再console中执行下列代码：

root = r'C:\Users\admin\PycharmProjects\py_projects\pytorch_learning\mnist'
raw_folder='raw'
filenames=['train-images-idx3-ubyte.gz','train-labels-idx1-ubyte.gz','t10k-images-idx3-ubyte.gz','t10k-labels-idx1-ubyte.gz']
import os
import gzip
for filename in filenames:
    file_path=os.path.join(root, raw_folder, filename)
    with open(file_path.replace('.gz', ''), 'wb') as out_f, \
            gzip.GzipFile(file_path) as zip_f:
        out_f.write(zip_f.read())
    os.unlink(file_path)    
    
from __future__ import print_function
import torch.utils.data as data
from PIL import Image
import os
import os.path
import errno
import numpy as np
import torch
import codecs
def get_int(b):
    return int(codecs.encode(b, 'hex'), 16)
def read_label_file(path):
    with open(path, 'rb') as f:
        data = f.read()
        assert get_int(data[:4]) == 2049
        length = get_int(data[4:8])
        parsed = np.frombuffer(data, dtype=np.uint8, offset=8)
        return torch.from_numpy(parsed).view(length).long()
def read_image_file(path):
    with open(path, 'rb') as f:
        data = f.read()
        assert get_int(data[:4]) == 2051
        length = get_int(data[4:8])
        num_rows = get_int(data[8:12])
        num_cols = get_int(data[12:16])
        images = []
        parsed = np.frombuffer(data, dtype=np.uint8, offset=16)
        return torch.from_numpy(parsed).view(length, num_rows, num_cols)
    
splits = ('byclass', 'bymerge', 'balanced', 'letters', 'digits', 'mnist')

def _training_file(self, split):
    return 'training_{}.pt'.format(split)
def _test_file(self, split):
    return 'test_{}.pt'.format(split)

raw_folder = os.path.join(root, raw_folder)
gzip_folder = os.path.join(raw_folder, 'gzip')

raw_folder='raw'
processed_folder='processed'
training_file = 'training.pt'
test_file = 'test.pt'

training_set = (
    read_image_file(os.path.join(root, raw_folder, 'train-images-idx3-ubyte')),
    read_label_file(os.path.join(root, raw_folder, 'train-labels-idx1-ubyte'))
)
test_set = (
    read_image_file(os.path.join(root, raw_folder, 't10k-images-idx3-ubyte')),
    read_label_file(os.path.join(root, raw_folder, 't10k-labels-idx1-ubyte'))
)
with open(os.path.join(root, processed_folder, training_file), 'wb') as f:
    torch.save(training_set, f)
with open(os.path.join(root, processed_folder, test_file), 'wb') as f:
    torch.save(test_set, f)
print('Done!')
Done!

结果：raw中变成了

processed文件夹中变成了：

这样的结果等价于

torchvision.datasets.MNIST下载的结果，现在只需要将

DOWNLOAD_MNIST的值设置为False，直接可以运行程序。

源代码：https://github.com/MorvanZhou/PyTorch-Tutorial/blob/master/tutorial-contents/401_CNN.py