numpy permutation issue

Hi, I just want to understand the rules of the permutation used in numpy
see this is the code used in example2

```
import numpy as np

shuffle_index = np.random.permutation(60000)
X_train, y_train = X_train[shuffle_index], y_train[shuffle_index]
```

well, let us use 6 instead of 60000. So after run the 1st code, the `shuffle_index` could be:
[4,5,2,6,3,1], it is an array, right?

then I can not understand the `X_train[shuffle_index]`, so it is what? `X_train[[4,5,2,6,3,1]]`, I guess we want the `X_train` can be ordered as `X_train[4], X_train[5], X_train[2]...`. but this can be done by `X_train[shuffle_index]`?