convert strings to number array from file python : i have a text file like this

**.txt**

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

and i would like to view this as an array in python  this is what i have so far

**python file**

     file_board = open('index.txt')
     board = file_board.read().split(',')
     print board
     print len(board)


**output**

    ['[[1', ' 2', ' 3]', ' [4', ' 5', ' 6]', ' [7', ' 8', ' 9]]\n']
    9
    list index out of range

so what i want todo is some how make this in to a 2D array  for manipulation 

**Note** I would like to do this without any external libraries, build in libraries are fine 