Python file structure

[Ned Batchelder]

On Tuesday, May 12, 2015 at 3:13:32 PM UTC-4, zljubi... at gmail.com wrote:
> Hi, I have python file with the following structure:
> 
> import...
> 
> A = configparser.get(...) 
> B = configparser.get(...)
> 
> Command line parameters parsing [they can change variable A or B]
> 
> Def usage()
> 	Print how to use script parameters
> 
> def main():
> 	...
> 
> if __name__ == "__main__":
>     main()
> 
> If I find an error in command line parameters section I cannot call function usage() because it is not defined yet. 
> 
> I have few options here:
> 1.	Put definition of usage function before command line parameters parsing section
> 2.	Make parameters global and put them in the main function
> 3.	...maybe some other options...
> 

I would put all of the code into a function some place.  Don't have
anything at the top level of the file except imports, function (and
class) definitions, and an "if __name__....." clause at the bottom.

If you need to use globals, assign them inside a parse_arguments
function that has a "global" statement in it.

This advice is consistent with Chris' "define things before they
are used."  It does it by defining everything before anything is
run.

As a side note, if you are going to have code at the top-level of
the file, then there's no point in the "if __name__..." clause.
That clause is designed to make a file both runnable and importable.
But your top-level code makes the file very difficult to import.

--Ned.