How to handle invalid arguments with argparse in Python?

We rewrite the given code as follows

#foo.py
import argparse
class InvalidArgError(Exception):pass
parser = argparse.ArgumentParser()
parser.add_argument("echo")
args = parser.parse_args()
try:
print (args.echo)
raise InvalidArgError
except InvalidArgError as e:
print e

When this script is run at the terminal as follows

$ python foo.py echo bar

We get the following output

usage: foo.py [-h] echo
foo.py: error: unrecognized arguments: bar