Python argparse: diiference between -o and --option

Question

I am trying to understand the argparse package and I really can't find an answer to this very simple question:

• What is the difference between -a and --argument when adding an argument?

Sometimes, I find both in one add_argument() like here:

parser.add_argument(
        "-f", "--file",
        help="file path"
        )

Answer 1

If both are specified, then argparse will store the value in the long form ('argument') rather than the short form ('a'). It will infer the destination, so "--foo-bar" will be stored in foo_bar.

You can mash together short forms and use a single hyphen (-af) but unlike some *NIX commands, order is important: If your argument requires a value (-f filename) then the argument must appear as the final argument of the group of short-form arguments:

cmd -af my_file   # works
cmd -fa my_file   # does not work

Compare this with the monster tar(1) which allows tar -cfC myfile.tar ./directory and will correctly sort it out as logically equivalent to tar -c -f myfile.tar -C ./directory. Also, some long forms allow the use of '=' when specifying the option tar -cf myfile.tar, versus tar -c --file=myfile.tar. You cannot use '=' on short forms.

Fortunately, python argparse doesn't care about '='. Use it or not, with short form or long form.

# All equivalent:
  cmd -af=my_file
  cmd -a -f my_file
  cmd -a -fmy_file
  cmd -afmy_file
  cmd --file my_file -a
  cmd --file=my_file -a

Does it matter? As another answer suggests, the long form can help with readability. Short form can make your power-users happier.