Python 关于 name main的使用

原文地址：
http://www.cnblogs.com/herbert/archive/2011/09/27/2193482.html

看过很多python的code都有这段代码：

if __name__ == '__main__':

这段代码的主要作用主要是让该python文件既可以独立运行，也可以当做模块导入到其他文件。当导入到其他的脚本文件的时候，该main代码里面的就不执行了。

参考：

The if __name__ == "__main__": ... trick exists in Python so that our Python files can act as either reusable modules, or as standalone programs. As a toy example, let's say that we have two files:

mumak:~ dyoo$ cat mymath.py
def square(x):
    return x * x

if __name__ == '__main__':
    print "test: square(42) ==", square(42)


mumak:~ dyoo$ cat mygame.py
import mymath

print "this is mygame."
print mymath.square(17) 

In this example, we've written mymath.py to be both used as a utility module, as well as a standalone program. We can run mymath standalone by doing this:

mumak:~ dyoo$ python mymath.py
test: square(42) == 1764 

But we can also use mymath.py as a module; let's see what happens when we run mygame.py:

mumak:~ dyoo$ python mygame.py
this is mygame.
289 

Notice that here we don't see the 'test' line that mymath.py had near the bottom of its code. That's because, in this context, mymath is not the main program. That's what the if __name__ == "__main__": ... trick is used for.

 

在这个例子里面mygame.py里面调用square函数的时候，就不会执行mymath.py里面的main函数了。