getting the LIST of empty squares of a grid

[jone kim]

grid = [[0,0,0][0,0,0][0,0,0]]

user fills the gird simultaneously. Now I want to make a list of empty squaes of the gird.

Suppose user has filled: grid [col1][row1] , grid [col3][row1], grid [col3][row2].

Now I need a list with indexes of the empty list i.e.

emptyGrid = [1,2,4,5,7,8,9]

First I've to found out which squares are empty then keep the indexes of those squares in a LIST. But how can I do it??

How can I do it?