 load the  readable data
 load the  readable data

```py
dataset = np.ndarray(shape=(len(image_files), image_size, image_size),
                         dtype=np.float32)
for image_index, image in enumerate(image_files):
    ...
num_images = image_index + 1
dataset = dataset[0:num_images, :, :]
```
By doing so, `num_images` will always equal to `len(image_files)`. 
So  the code here, `dataset = dataset[0:num_images, :, :]` cannot  select the valid (readable) images.
But from the output, it works just fine. 
Why it work fine??
I think the job can be done by the following code.
```py
dataset = np.ndarray(shape=(len(image_files), image_size, image_size),
                         dtype=np.float32)
num_images = 0
for  image in image_files:
    ...
    num_images =  num_images + 1
dataset = dataset[0:num_images, :, :]
```"
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