What does this mean exit (main())

Question

I have seen this in a couple of python script I have been reading lately. I have looked at the doc; they only give examples deal with passing a termination value or string of some sort.

I think what this does is call the main method, then exit?

If someone could shed some light on this I would appreciate it.

if __name__ == "__main__":    exit (main()) 

Please and thank you

Answer 1

This will call the function main() and when main finishes, it will exit giving the system the return code that is the result of main().

A simplified example where this might be used:

def main():     try:         doSomething()         return 0     except:         return 1   if __name__ == "__main__":     exit (main()) 

If an explicit return value is not given in main(), the default value of None will be returned. This produces the same system return code as explicitly specifying return 0. If main returns anything other than an integer or None a system return code of 1 will be produced.

Answer 2

If you execute a Python script directly, __name__ is set to "__main__", but if you import it from another script, it is not.

So in this case, the script is seeing if you're executing it directly. If it is, it calls the main() function to perform some work, and returns the return value of the main() function to the system via exit(). If the script is being imported from another module, it doesn't execute the main() function and simply provides the script's functions and classes to the importing script.

This is a common idiom in Python. It allows you to have scripts that are standalone programs, but can also be imported without trying to do work that the importing script doesn't want done.