Is there any advantage to using a main() in python scripts?
rustompmody at gmail.com
Wed Dec 11 15:24:26 CET 2013
On Wednesday, December 11, 2013 7:47:34 PM UTC+5:30, Roy Smith wrote:
> JL 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.
I guess these are important but somewhat advanced considerations.
For a beginner, its important to get that there is a bit of a pun here:
The function habitually called 'main' may be called that or anything else
It can have or not have an argument as Ben pointed out -- maybe more than
The module name __main__ is however sacrosanct and hardwired into python.
The habit of connecting the one with the other is partly conventional and
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