来自python 文档:

使用以下命令运行Python模块时

When you run a Python module with

python fibo.py

python fibo.py

模块中的代码将为 被执行，就像您导入它一样 但__name__设置为 "__main__".这意味着通过添加 此代码在您的模块末尾:

the code in the module will be executed, just as if you imported it, but with the __name__ set to "__main__". That means that by adding this code at the end of your module:

if __name__ == '__main__':
    # Running as a script

您可以将文件用作脚本以及可导入的模块，因为解析命令行的代码仅在将模块作为主"文件执行时才运行

you can make the file usable as a script as well as an importable module, because the code that parses the command line only runs if the module is executed as the "main" file