Python 关于 name main的使用

看过很多python的code都有这段代码：

if __name__ == '__main__':
    statements

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，此时__name__的名字其实是导入模块的名字，不是'__main__', main代码里面的就不执行了。

比如有这样的一个文件test.py, 里面代码如下：

# test.py

def test():
    print("Test function.")

if __name__ == '__main__':
    test()

 当按F5的时候可以独立运行程序，结果：

>>> ================================ RESTART ================================
>>> 
Test function.
>>> print(__name__)
__main__
>>>

 但是也可以作为模块import使用，结果：

>>> import test
>>> test.test
<function test at 0x0000000003455F28>
>>> test.test()
Test function.

参考：

http://pyfaq.infogami.com/tutor-what-is-if-name-main-for

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

mymath.py文件

def square(x):
    return x * x

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

mumak:~ dyoo$ cat mygame.py

mygame.py 文件

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。