$ ls
cpython devguide prog.py pypy rm-unused-function.patch
$ ls pypy
ctypes_configure demo dotviewer include lib_pypy lib-python ...
$ ls -l
total 20
drwxr-xr-x 19 wena wena 4096 Feb 18 18:51 cpython
drwxr-xr-x 4 wena wena 4096 Feb 8 12:04 devguide
-rwxr-xr-x 1 wena wena 535 Feb 19 00:05 prog.py
drwxr-xr-x 14 wena wena 4096 Feb 7 00:59 pypy
-rw-r--r-- 1 wena wena 741 Feb 18 01:01 rm-unused-function.patch
$ ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

import argparse
parser = argparse.ArgumentParser()
parser.parse_args()

$ python prog.py
$ python prog.py --help
usage: prog.py [-h]

optional arguments:
 -h, --help show this help message and exit
$ python prog.py --verbose
usage: prog.py [-h]
prog.py: error: unrecognized arguments: --verbose
$ python prog.py foo
usage: prog.py [-h]
prog.py: error: unrecognized arguments: foo

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("echo")
args = parser.parse_args()
print args.echo

$ python prog.py
usage: prog.py [-h] echo
prog.py: error: the following arguments are required: echo
$ python prog.py --help
usage: prog.py [-h] echo

positional arguments:
 echo

optional arguments:
 -h, --help show this help message and exit
$ python prog.py foo
foo

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("echo", help="echo the string you use here")
args = parser.parse_args()
print args.echo

$ python prog.py -h
usage: prog.py [-h] echo

positional arguments:
 echo    echo the string you use here

optional arguments:
 -h, --help show this help message and exit

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", help="display a square of a given number")
args = parser.parse_args()
print args.square**2

$ python prog.py 4
Traceback (most recent call last):
 File "prog.py", line 5, in <module>
  print args.square**2
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", help="display a square of a given number",
          type=int)
args = parser.parse_args()
print args.square**2

$ python prog.py 4
16
$ python prog.py four
usage: prog.py [-h] square
prog.py: error: argument square: invalid int value: 'four'