error

[woooee]

>From this line, "data" appears to be a class
    if 0 < ix < data.width and 0 < iy < data.height:
>From this line, "data" appears to be a list, although a two
dimensional list would be accessed as data[ix][iy]
        point = data[ix, iy]

Also, returning a list from a function is a matter of preference.
Some people argue that it should be returned to make it obvious.  If
you do not know the difference between what is mutable and what is not
mutable, then return everything until you do.