Is there any advantage to using a main() in python scripts?

[Roy Smith]

In article <32615c9a-b983-4399-bb55-6df6c230f247 at googlegroups.com>,
 JL <lightaiyee at gmail.com> wrote:

> Python scripts can run without a main(). What is the advantage to using a 
> main()? Is it necessary to use a main() when the script uses command line 
> arguments? (See script below)
> 
> #!/usr/bin/python
> 
> import sys
> 
> def main():
>     # print command line arguments
>     for arg in sys.argv[1:]:
>         print arg
> 
> if __name__ == "__main__":
>     main()

No, it's not necessary, but it's a good idea.

For one thing, it lets you import your script without actually running 
it.  We recently tracked down a long-standing bug where some maintenance 
script we had started out with:

import os
os.environ['DJANGO_SETTINGS_MODULE'] = 'whatever'

somebody imported that script in another part of the system because 
there was some convenient definition that he wanted to reuse.  
Unfortunately, the act of importing the script changed the environment!

The fix was to move the setting of the environment variable to inside 
the main() routine.  If you always follow the rule that you always put 
all your executable code inside main(), you'll never run into problems 
like that.