Python numpy, ask me a question

The front row and the back row are the columns.

Slicing 0:2 columns in row 0:2

lst = [
    [1,2,3],
    [4,5,6],
    [7,8,9]
    ]

arr = np.array(lst)

The first subscript is for a row.

arr[0] only slices the first row. [1 2 3]

arr[0:2] slices to the second row. [[1 2 3] [4 5 6]]

The last subscript is about heat.

arr[0, 0:2] Slice only two columns in the first row. [1 2]

arr[0:2, 0:2] slices two columns in two rows. [[1 2] [4 5]]