Edit: How to return/serve a file from a python controller (back end) over a web server, with the file_name? as suggested by @JV
You can either pass back a reference to the file itself i.e. the full path to the file. Then you can open the file or otherwise manipulate it.
Or, the more normal case is to pass back the file handle, and, use the standard read/write operations on the file handle.
It is not recommended to pass the actual data as files can be arbiterally large and the program could run out of memory.
In your case, you probably want to return a tuple containing the open file handle, the file name and any other meta data you are interested in.
Return file from python module