arr = [[1, 2],[3, 4]]
#del arr[1]
print ( arr[0][0] )
arr[0].append(3)
print ( arr[0] )

arr02 = [ [], [] ]
arr02[0].append(1)
print ( arr02[0] )
arr02.append([])
print ( arr02 )

l2_arr = [5, 6]
arr02[2] =l2_arr
print ( arr02 )
arr02[2].append(7)
print ( arr02 )