I found my log file here:
C:\Documents and Settings\<your profile name>\Local Settings\Temp\Filter Forge x86.log
FF, you should consider adding an option for clearing that logfile when a rendering starts. It seems you just append to that logfile during the whole FF session
I'm looking at a 233 MB logfile right now

- Yes I know I shouldn't put print calls inside get_sample .. but it is very helpful when debugging.
Beside from that "print" is not in the unsafe function category, meaning that it is possible to submit a filter that might fill up the disk with a huge logfile...