Python argparse ignore unrecognised arguments

Question

Optparse, the old version just ignores all unrecognised arguments and carries on. In most situations, this isn't ideal and was changed in argparse. But there are a few situations where you want to ignore any unrecognised arguments and parse the ones you've specified.

For example:

parser = argparse.ArgumentParser()
parser.add_argument('--foo', dest="foo")
parser.parse_args()

$python myscript.py --foo 1 --bar 2
error: unrecognized arguments: --bar

Is there anyway to overwrite this?

Answer 1

Replace

args = parser.parse_args()

with

args, unknown = parser.parse_known_args()

For example,

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--foo')
args, unknown = parser.parse_known_args(['--foo', 'BAR', 'spam'])
print(args)
# Namespace(foo='BAR')
print(unknown)
# ['spam']

Answer 2

You can puts the remaining parts into a new argument with parser.add_argument('args', nargs=argparse.REMAINDER) if you want to use them.

Answer 3

Actually argparse does still "ignore" _unrecognized_args. As long as these "unrecognized" arguments don't use the default prefix you will hear no complaints from the parser.

Using @anutbu's configuration but with the standard parse.parse_args(), if we were to execute our program with the following arguments.

$ program --foo BAR a b +cd e

We will have this Namespaced data collection to work with.

Namespace(_unrecognized_args=['a', 'b', '+cd', 'e'], foo='BAR')

If we wanted the default prefix - ignored we could change the ArgumentParser and decide we are going to use a + for our "recognized" arguments instead.

parser = argparse.ArgumentParser(prefix_chars='+')
parser.add_argument('+cd')

The same command will produce

Namespace(_unrecognized_args=['--foo', 'BAR', 'a', 'b'], cd='e')

Put that in your pipe and smoke it =)

nJoy!