#how to open file with the default application for that file set by the OS

import os

filename = "PATH_TO_FILE" # EG. "C:\Users\baguette\Downloads\image.png"

os.system("open " + shlex.quote(filename)) #MacOS/X
os.system("start " + filename) #windows

#Information and more available at 
#https://stackoverflow.com/questions/434597/open-document-with-default-os-application-in-python-both-in-windows-and-mac-os