pyinstaller can package a python app into a single executable file. When this executable file runs, it's first extracted into a temporary location then the python script is called. The usual loading of files with relative path would not work. The following code is found online to work around this issue.

abspath_pyinstaller.py

def abspath(filename):
    # looking for magic word _MEIPASS
    bundle_dir = getattr(sys, '_MEIPASS', os.path.abspath(os.path.dirname(__file__)))
    return os.path.abspath(os.path.join(bundle_dir, filename))