cs at cskk.id.au
Thu Jul 5 19:21:13 EDT 2018
On 05Jul2018 11:22, Rhodri James <rhodri at kynesim.co.uk> wrote:
>On 05/07/18 09:43, Abdur-Rahmaan Janhangeer wrote:
>>just when to use main() in
>>if __name__ == '__main__' :
>>is far is it good in py?
>>or should file intended to be run just not include it?
>It's a matter of taste. If your "file intended to be run" also
>contains things that might be useful as a module, use the "if __name__
>== '__main__'" trick. Otherwise it can be more of a distraction than
>a help. I'm not a big fan of "main()" functions myself; creating a function
>which will be called exactly once seems rather wasteful.
I almost always make a main. For several of my modules there's a meaningful
command line mode, and for most of the rest I make main run the self tests.
The main function has some advantages:
- I put it at the top of the module, before anything other functions: that way
the "main" operation of the module, if there is one, is in your face them you
open the file, easy to find. Also, it is _immediately_ apparent that this
module has a "main programme" mode.
- You don't need to call it just once. Making a main() function, should it make
sense, lets you call it _from other code_. Consider a wrapper which relies on
the main function of this module for the core command line operation, or
which runs this module's main as some kind of "subcommand" in a larger tool,
such as most VCS commands, GraphicsMagick, etc - all have subcommandswhich
are effectively standalone things in their own right.
I also advocate making the boilerplate like this:
if __name__ == '__main__':
and make main() like this:
if argv is None:
argv = sys.argv
... code here ...
The "argv is None" shuffle is for PyPI packaging, where the standard script
wrapper _doesn't_ pass in sys.argv, (no idea why, I should submit an
enhancement proposal). Otherwise, there's argv, ready for reuse of the main()
function from arbitrary code.
Cameron Simpson <cs at cskk.id.au>
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