Hi All,

I've been using the argparse library for a long time and one use case that repeatedly shows us is the need to have two arguments appear together i.e either both appear or none of them appear. I'll refer to these as *mutually inclusive* in contrast to the existing *mutual exclusive* feature present. I might be wrong but there seems to be no way to enforce this. Of course it is possible to have two arguments that are *required* but it's not always the case that they will be needed.

A more relevant example would be a situation in which you have a set of mutually exclusive arguments, one of which is a group of arguments. For example, consider a scenario in which a user is required to enter multiple related files that share the same file root (excluding the extension). The program would then infer the various files (co-files) by searching for the extensions. The first option would have the user only need to provide the file name root. However, the user may also provide the paths to the various co-files. In this case, the co-files must occur together but must occur mutually-exclusively from the file root option.

Another example would be a case in which activating one set of options implies the need for other options to be simultaneously activated and for which defaults may not be easily discerned. Quite often the author has to perform pythonic gymnastics to catch such invalid options, which might be better handled by the argparse library.

In evaluating the need for this I've come across the following responses:

I perceive there is a compelling use-case to be addressed here despite an earlier request being turned down.