def _still_to_download(file_names, target_path):
    'Only return the files that are not yet present on disk.'
    for fn in list(file_names):
        if os.path.exists(os.path.join(target_path, fn)):
            file_names.remove(fn)
    return file_names
Only return the files that are not yet present on disk.
def _still_to_download(file_names, target_path):
    
    for fn in list(file_names):
        if os.path.exists(os.path.join(target_path, fn)):
            file_names.remove(fn)
    return file_names