In this case of `fla` I agree.  I think `fnu` less so.  I think better still would just be `F_lambda` and `F_nu` (the former is fine since even though lambda is a keyword in Python, here's a substring of a variable name so that's okay).  In this case it's almost exactly how you would write these values in LaTeX.  In any case, this is just nitpicking ;)