如何从不同的目录中选择20个文件，Python？

def select_files(directory):
    global count
    for root, dirs, files in os.walk(directory):
        for file in files:
            file_path = os.path.join(root, file)
            selected_files.append(file_path)
            count += 1
            if count == 20:
                return

select_files('/path/to/directory1')
select_files('/path/to/directory2')
# 继续选择其他目录...