dealing with spaces in file names

[AceScottie]

I never actually define the string manually it's just pulled from os.listdir() so I can't add the r to the start of the string

os.listdir() just return filename,so why should you add r(raw string)?
If you build path yourself then can r or \\ or / just not singel \ because of escape charterer.
Maybe i misunderstand you,so it's better that you post code and explain what's not working.

Here using listdir and open in Notepad default Windows application.
Now i just working from current folder so no path is needed.

>>> import webbrowser
>>> import os
>>> 
>>> lst = os.listdir('.')
>>> lst
['c.py', 'cpt.py', 'f.py', 'html_env', 'path.py', 'test file.txt']
>>> webbrowser.open(lst[-1])
True 

Webbroweser is the best module i was looking for.
it fixes the file name issue and also opens the "open with" window for non associated files
Thansk