I want to define a two-dimensional array without an initialized length like this :
Matrix = 
>>> Matrix = 
IndexError: list index out of range
You're technically trying to index an uninitialized array. You have to first initialize the outer list with lists before adding items; Python calls this "list comprehension".
# Creates a list containing 5 lists, each of 8 items, all set to 0 w, h = 8, 5. Matrix = [[0 for x in range(w)] for y in range(h)]
Matrix = 1 Matrix = 3 # error! range... Matrix = 3 # valid print Matrix # prints 1 x, y = 0, 6 print Matrix[x][y] # prints 3; be careful with indexing!
Although you can name them as you wish, I look at it this way to avoid some confusion that could arise with the indexing, if you use "x" for both the inner and outer lists, and want a non-square Matrix.