argparse: some mutually exclusive arguments in required group

Question

I have a set of arguments that can logically be separated in 2 groups:

• Actions: A1, A2, A3, etc.
• Informations: I1, I2, I3, etc.

At least one of these arguments is required for the program to start, but "information" args can be used with "action" args. So

• At least one in Actions or Informations is required
• All Actions are mutually exclusive

I can't find how to do it using argparse. I know about add_mutually_exclusive_group and its required argument, but I can't use it on "Actions" because it's not actually required. Of course, I could add a condition after argparse to manually check my rules, but it seems like an hack. Can argparse do this?

Edit: Sorry, here are some examples.

# Should pass
--A1
--I1
--A1 --I2
--A2 --I1 --I2

# Shouldn't pass
--A1 --A2
--A1 --A2 --I1

Answer 1

There's nothing hacky about verifying arguments after they've been parsed. Just collect them all in a single set, then confirm that it is not empty and contains at most one action.

actions = {"a1", "a2", "a3"}
informations = {"i1", "i2", "i3"}
p = argparse.ArgumentParser()
# Contents of actions and informations contrived
# to make the example short. You may need a series
# of calls to add_argument to define the options and
# constants properly
for ai in actions + informations:
    p.add_argument("--" + ai, action='append_const', const=ai, dest=infoactions)

args = p.parse_args()
if not args.infoactions:
    p.error("At least one action or information required")
elif len(actions.intersection(args.infoactions)) > 1:
    p.error("At most one action allowed")