Is it possible to have 2 actions on argparse argument?

Question

like the title says, I have a parser that has to do 2 things on an argument,

it has to append a const to a list (a list that gives the program all the functions it has to process)
it has to add the value after this argument to a variable, so it can be used later

some code of the parser (will fail, as defining 2 times '-copy' wont work:

parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter, description="""some help text""") # ... more arguments, but not a problem parser.add_argument('-ls','--list',action='append_const', dest='tasks',const=ls, help='outputs the filelocation if match was found') parser.add_argument('-copy', action='append_const', dest='tasks',const=copy, help='copies the file to the given location if a match was found') parser.add_argument('-copy', dest='copyLocation', help='outputs the filelocation if match was found')

anyone an idea of how to work around this and make the -copy argument do both a store and a append_const?

I know I could just 'postprocess' the args and check if there is a -copy in it, and if so then add the function copy to the list tasks. But this seams like a workaround, so I hoped there is a better way of doing things without postprocessing the arguments.

Why don't you add another argument, then argument #1 does thing #1 and argument #2 does thing #2? — Bogdan Doicin
– Bogdan Doicin, Commented Jun 5, 2019 at 9:27
those custom actions look promising :D, thanks I will look at them directly! — Joris D R.
– Joris D R., Commented Jun 5, 2019 at 9:30

Joris D R. · Accepted Answer · 2019-06-05 10:17:34Z

thanks to the comment on custom actions I found a nice way of adding this :)

#custom action for store and append_const class StoreValueAndAppendConst(argparse.Action): def __init__(self, option_strings, dest, nargs=None, **kwargs): if nargs is not None: raise ValueError("nargs not allowed") if "task" in kwargs: self.task = kwargs["task"] del kwargs["task"] super(StoreValueAndAppendConst, self).__init__(option_strings, dest, **kwargs) def __call__(self, parser, namespace, values, option_string=None): #add the task to the list of tasks. if not namespace.tasks: namespace.tasks = [] namespace.tasks.append(self.task) setattr(namespace, self.dest, values) #do the normal store

and the actually calling changes into:

parser.add_argument('-copy', action=StoreValueAndAppendConst, dest='copy', task=copy, help='outputs the filelocation if match was found')

I might be able to make the custom function more generic, but this is enough for this case.

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