if __name__ == '__main__'

__name__ == '__main__'

# /home/main_one.py
def func():
    print("func() in one.py")

print("top-level in one.py")

if __name__ == "__main__":
    print("one.py is being run directly")
else:
    print("one.py is being imported into another module")

# /home/main_two.py
import main_one

print("top-level in two.py")
main_one.func()

if __name__ == "__main__":
    print("two.py is being run directly")
else:
    print("two.py is being imported into another module")

运行main_one.py，输出

top-level in one.py
one.py is being run directly

运行main_two.py，输出

top-level in one.py
one.py is being imported into another module
top-level in two.py
func() in one.py
two.py is being run directly

我的理解

当一个A脚本被执行时，这时A脚本的__name__ 和"__main__)"就相等

当在B脚本导入A脚本，B脚本执行时，这时A脚本的__name__ 和"__main__)"就不相等

关于main_two.py执行的问题

对导入的模块来说，模块中的函数是调用时才执行的，但是语句会立刻执行（那些没有缩进的语句）

参考知乎