For reasons well outside the scope of this entry, the other day I looked at the --help output from one of my old Python programs. This particular program has a lot of options, but when I'd written it, I had used argparse argument groups to break up the large list of options into logical groups, starting with the most important and running down to the 'you should probably ignore these' ones. The result was far more readable than it would have been without the grouping.

(I want to call these 'option groups', because that's what I use them for.)

I've regularly used mutual exclusion groups in my recent Python programs, but for some reason I've fallen so much out of the habit of using argparse groups to break up walls of options that I'd forgot they even existed until I was reminded by my own program's --help output. Now that I've been reminded, there are probably some programs that I should go back to and add some groups to.

(Most or all of my programs with a lot of options have a structure to them; it's not just a kitchen sink of a lot of things. Even if there is no real structure I can at least separate things into frequent, less frequent, and obscure options.)

Although you can't put either sort of group inside a mutual exclusion group , the argparse documentation is explicit that you can put a mutual exclusion group inside a regular argument group (a detail that I hadn't remembered until I reread my entry on this ). Now that I look, one reason to do this is so that you can give the block of mutually exclusive options a title and description that actually tells people that they're mutually exclusive.

(Maybe it would be nicer if a a mutual exclusion group could have an optional title and description, but that's not the API we have.)

As the argparse documentation says, anything not in an argument group is put in the usual sections in your --help. Another way to put this is that the moment you put something in an argument group, it drops down to the bottom of your remaining regular --help output (with a blank line between the regular help and the argument groups). Then each argument group is separated from the next with a blank line, whether or not you gave them a title or a description.

My view is that this can make argument groups a relatively all or nothing thing. If you just want to put a blank line and a title to group your already properly ordered options into digestible chunks, the only ones you can leave out of a group are the first options. After you add the first group, everything afterward has to also be in a group or it will get reordered on you. Fortunately this is easy to do in the sort of code I tend to write to set up argparse stuff, but I'm going to have to remember it when I start adding argument groups to my programs.

(Argparse --help prints options in the order you defined them, so it's conventional to put the most important options first and the least important ones last.)