${WING:FILENAME} example needed

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I have tried so many ways to use ${WING:FILENAME} in my script, that I am out of ideas. In my script, I want to use the filename of the script as a variable. So simply put, I want something like this:

fileName = ${WING:FILENAME}

After reading https://wingware.com/doc/proj/variabl... I tried just about every combination, including os.environ.get, but I keep getting a syntax error on ${WING:FILENAME}. I am positive I am just making a stupid mistake in my thought process somewhere, but I just need to be able to use this variable. So I need help :-/