atexit not being executed

[Chris Gorton]

I am currently writing some code within a Data Quality tool that allows for 
transforms to pass data records through what they call User Defined 
Transforms (This transforms allow access to all python functionality). It is 
currently using version 2.3

My problem is as follows:

I am calling an API and obtaining a thread id via the ctypes module, 
performing my required tasks then outputting the appended data as required. 
This then runs for every record within the file with the exception of 
re-initialising the DLL (This is only performed once to improve 
performance). Everything is working fine however I have no way of knowing 
when all of the data records have passed through the transform so that I can 
call the 'close' function supplied within the API. I tried looking through 
the documentation and came across atexit. I tried putting this into my code 
and it never seems to actually process the atexit.register(....) function 
thus leaving me stranded. My question is what might be the reason for this 
happening (The company support are not too helpful in this matter) and are 
there any other possible ways that I might be able to overcome this problem 
that I seem to have.