Josh Rosenberg <[email protected]> added the comment:
That's a *really* niche use case; you want to store everything to a common
destination list, in order, but distinguish which switch added each one? I
don't know of any programs that use such a design outside of Python (and
therefore, it seems unlikely there would be enough demand from argparse users
to justify the development, maintenance, and complexity cost of adding it).
argparse does support defining custom Actions, so it's wholly possible to add
this sort of support for yourself if there isn't enough demand to add it to
argparse itself. For example, a simple implementation would be:
class AppendWithSwitchAction(argparse.Action):
def __init__(self, option_strings, dest, *args, **kwargs):
super().__init__(option_strings, dest, *args, **kwargs)
# Map all possible switches to the final switch provided
# so we store a consistent switch name
self.option_map = dict.fromkeys(option_strings, option_strings[-1])
def __call__(self, parser, namespace, values, option_string=None):
option = self.option_map.get(option_string)
try:
getattr(namespace, self.dest).append((option, value))
except AttributeError:
setattr(namespace, self.dest, [(option, value)])
then use it with:
parser.add_argument('-p', '--preload', help='preload asset',
action=AppendWithSwitchAction, metavar='NAMESPACE')
parser.add_argument('-f', '--file', help='preload file',
action=AppendWithSwitchAction, metavar='FILE', dest='preload')
All that does is append ('--preload', argument) or ('--file', argument) instead
of just appending the argument, so you can distinguish one from the other (for
switch, arg in args.preload:, then test if switch=='--preload' or '--file').
It's bare bones (the actual class underlying the 'append' action ensures nargs
isn't 0, and that if const is provided, nargs is '?'), but it would serve.
----------
nosy: +josh.r
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<https://bugs.python.org/issue34458>
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