为什么manage.py运行两次？

Question

我在django项目中的manage.py文件中有以下代码：

SELECT MINVE01.DATE_DOCU, INVE01.LIN AS LINE
FROM MINVE01 left outer join INVE01 on INVE01.CVE_ART=MINVE01.CVE_ART
GROUP BY MINVE01.DATE_DOCU, INVE01.LIN

我得到了这个输出：

if __name__ == "__main__":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "settings")
    from django.core.management import execute_from_command_line

    print 'command for running'

    execute_from_command_line(sys.argv)

为什么$ python manage.py runserver command for running command for running Performing system checks... ... 打印两次？