Posted By: Anonymous
I want to define a two-dimensional array without an initialized length like this:
Matrix = 
but it does not work…
I’ve tried the code below, but it is wrong too:
Matrix = 
Traceback ... IndexError: list index out of range
What is my mistake?
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
# 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)]
You can now add items to the list:
Matrix = 1 Matrix = 3 # error! range... Matrix = 3 # valid
Note that the matrix is “y” address major, in other words, the “y index” comes before the “x index”.
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.