Using 'argparse.ArgumentError' in Python

Question

I\'d like to use the ArgumentError exception in the argparse module in Python, but I can\'t figure out how to use it. The signature says that it sh

Answer 1

While parser.error() is what most people probably want, it is also possible to use argparse.ArgumentError() (as the question asks.) You need a reference to the argument, like the bar_arg in the example below:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--foo')
bar_arg = parser.add_argument('--bar')

args = parser.parse_args()
if args.bar == 'xyzzy':
    raise argparse.ArgumentError(bar_arg, "Can't be 'xyzzy'")

if args.foo == 'xyzzy':
    parser.error("Can't be 'xyzzy'")

This will result in output like the one below:

$ python argparse_test.py --foo xyzzy
usage: argparse_test.py [-h] [--foo FOO] [--bar BAR]
argparse_test.py: error: Can't be 'xyzzy'

$ python argparse_test.py --bar xyzzy
Traceback (most recent call last):
  File "argparse_test.py", line 10, in 
    raise argparse.ArgumentError(bar_arg, "Can't be 'xyzzy'")
argparse.ArgumentError: argument --bar: Can't be 'xyzzy'