How to get past NaN value

[iFunKtion]

if avitime == None

gives exactly the same output. I just need to skip the whole file if the value is NaN on this particular occasion, though that is proving very difficult as I can't identify the file causing the probem, as they all open in a text file, some are empty or zero value on that element or they have the expected float, so it is difficult to understand what it is actually tripping up on, that's why I just want to completely skip the file is nan is present, but I can't find an answer.