How to determine if a file is busy?

[Busyman]

Hi,

I have written a stay-open-AppleScript for Mac OS X, gathering certain
informations from different apps, which can only be gathered via
AppleScript. This script writes its informations into a simple text
file, every 15 seconds. And a python script is supposed to read this
text file on a regular basis in order to feed the aquired datat into a
database working only on Windows. Now the problem: How can I prevent
that the python script reads the content of the text file, while my
AppleScripts writes new information to it? Is there any 'busy'-status
for files?

Thanks in advance from cold and cloudy Germany!

Martin