I have a folder called raw_files. Very large files (~100GB files) from several sources will be uploaded to this folder. 
I need to get file information from videos that have finished uploading to the folder. What is the best way to determine if a file is currently being downloaded to the folder (pass) or if the video has finished download (run script)? Thank you.
The most reliable way is to modify the uploading software if you can.
A typical scheme would be to first upload each file into a temporary directory on the same filesystem, and move to the final location when the upload is finished. Such a "move" operation is cheap and atomic.
A variation on this theme is to upload each file under a temporary name (e.g. file.dat.incomplete instead of file.dat) and then rename. You script will simply need to skip files called *.incomplete.
How to determing if a file has finished downloading in python