Python file structure

[Terry Reedy]

On 5/12/2015 3:49 PM, Ned Batchelder wrote:
> 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.

I was about to suggest the same.  One advantage of 'write tests first' 
is that you force yourself to write testable code from the beginning, 
instead of refactoring later.

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

Better not to have mutable module globals if you can avoid it.  If you 
want application globals, put them in a separate module.

> 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.

And you need to import to test.

-- 
Terry Jan Reedy