Problems using struct pack/unpack in files, and reading them.

[kent nyberg]

The main problem was that I forgot to do seek(0).  Thanks alot people.

Though, as many times before, the problem was due to misunderstanding of how python works.
I assumed file.read()[xx:yy] was to be understood as,   in the file, read from index xx to place yy.
That is,  [10:20]  was the same as,   read from 10th char to 20th.  Sort of.


Is it true then to say that every .read  of a file, places an index-offset (?) from where the next read starts?
That is, I need to rewind the file, or else the read will start from where the last read stopped?