Another solution is to make a runtime hook, which will copy(or move) your data (files/folders) to the directory at which the executable is stored. The hook is a simple python file that can almost do anything, just before the execution of your app. In order to set it, you should use the --runtime-hook=my_hook.py option of pyinstaller. So, in case your data is an images folder, you should run the command:
pyinstaller.py --onefile -F --add-data=images;images --runtime-hook=cp_images_hook.py main.py
The cp_images_hook.py could be something like this:
import sys
import os
import shutil
path = getattr(sys, '_MEIPASS', os.getcwd())
full_path = path+"\\images"
try:
shutil.move(full_path, ".\\images")
except:
print("Cannot create 'images' folder. Already exists.")
Before every execution the images folder is moved to the current directory (from the _MEIPASS folder), so the executable will always have access to it. In that way there is no need to modify your project's code.
You can take advantage of the runtime-hook mechanism and change the current directory, which is not a good practice according to some developers, but it works fine.
The hook code can be found below:
import sys
import os
path = getattr(sys, '_MEIPASS', os.getcwd())
os.chdir(path)