Hi
python under app engine can read files, it just can't write files to
the file system under gae.
So have a look at the getting started guide - for instance the Hello
World or the Template examples
and just modify them to read the csv and output it.
Its a pretty basic addition if you have worked out how to do file i/o
in python.
I suggest you work through the exmples and get use to the platform.
Rgds
T