NumPy arrays can have their elements accessed via the
 operator. There are many variants of this operator that we will see throughout this book, but the basic access to array elements is by passing the zero-based offset of the desired element:
In : # select 0-based elements 0 and 2 a1, a1 Out: (0, 2)
Elements in a two-dimensional array can be used by making use of two values separated by a comma, with the row first and column second:
In : # select an element in 2d array at row 1 column 2 m[1, 2] Out: 6
It is possible to retrieve an entire row of a two-dimensional array using just a single value representing the row and omitting the column component:
In : # all items in row 1 m[1,] Out: ...