How to check if it is running package file as main file

Run __main__

Modules defines functions and classes, and often we put test code which will run the functions and classes into the same file.

The following module has a function hello and a test run for it.

# hello.py # from   w  ww. ja v a 2  s. co m
def hello(): 
   print "Hello, world!" 

# A test: 
hello() 

If you import it as a module, the test code is executed:

import hello  #prints out Hello, world!
hello.hello() #prints out Hello, world! again

The first "Hello, world!" is printed by the hello function in the hello.py. The second "Hello, world!" is printed by hello.hello() in the main code.

Basically we need to tell whether a module is being run as a program on its own, or it is being imported into another program. To do that, you need the variable __name__. The __name__ stores the current running context. The __name__ is the value of __main__ when code is running under main program context. __name__ is the value of module name when running under module.

We can make your module's test code more well behaved by putting in an if statement.

# hello.py # from  w ww  .j a v a 2  s.  c  om

def hello(): 
    print "Hello, world!" 

def test(): 
    hello() 

if __name__ == '__main__': test() 



import hello 
hello.hello() #prints out Hello, world!