Returns a list of relative file paths to `path` for all files within `folder`

def read_dir(path, folder):
    """ Returns a list of relative file paths to `path` for all files within `folder` """
    full_path = os.path.join(path, folder)
    fnames = glob(f"{full_path}/*.*")
    directories = glob(f"{full_path}/*/")
    if any(fnames):
        return [os.path.relpath(f,path) for f in fnames]
    elif any(directories):
        raise FileNotFoundError("{} has subdirectories but contains no files. Is your directory structure is correct?".format(full_path))
    else:
        raise FileNotFoundError("{} folder doesn't exist or is empty".format(full_path))