We define positional arguments using a name with no "-" decoration. In a case where we have a fixed number of positional arguments, we'll add them appropriately to the parser, as shown in the following code:

parser.add_argument("input_filename", action="store") 
parser.add_argument("output_filename", action="store") 

When parsing argument values, the two positional argument strings will be stored in the final namespace object. We can use config.input_filename and config.output_filename to work with these argument values.

As noted previously, using simple positional parameters to identify output files can cause problems for users. The GNU/Linux cp, mv, and ln programs should be considered exceptional cases where a file can get overwritten. The preferred approach is to use an option with a value to specify the files that can be destroyed. It's almost always safer to force users to use an option like -o name.csv to make it perfectly clear what the output filename will be.