Question: I have a script which is meant to be used like this:
`usage: installer.py dir [-h] [-v]`

`dir` is a positional argument which is defined like this:

```
parser.add_argument('dir', default=os.getcwd())

```

I want the `dir` to be optional: when it's not specified it should just be `cwd`.

Unfortunately when I don't specify the `dir` argument, I get `Error: Too few arguments`.

Answer: 
Use [`nargs='?'`](https://docs.python.org/3/library/argparse.html#nargs) (or `nargs='*'` if you need more than one dir)

```
parser.add_argument('dir', nargs='?', default=os.getcwd())

```

extended example:

```
>>> import os, argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('-v', action='store_true')
_StoreTrueAction(option_strings=['-v'], dest='v', nargs=0, const=True, default=False, type=None, choices=None, help=None, metavar=None)
>>> parser.add_argument('dir', nargs='?', default=os.getcwd())
_StoreAction(option_strings=[], dest='dir', nargs='?', const=None, default='/home/vinay', type=None, choices=None, help=None, metavar=None)
>>> parser.parse_args('somedir -v'.split())
Namespace(dir='somedir', v=True)
>>> parser.parse_args('-v'.split())
Namespace(dir='/home/vinay', v=True)
>>> parser.parse_args(''.split())
Namespace(dir='/home/vinay', v=False)
>>> parser.parse_args(['somedir'])
Namespace(dir='somedir', v=False)
>>> parser.parse_args('somedir -h -v'.split())
usage: [-h] [-v] [dir]

positional arguments:
  dir

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

```
`parser.add_argument` also has a switch **required**. You can use `required=False`.
Here is a sample snippet with Python 2.7:

```
parser = argparse.ArgumentParser(description='get dir')
parser.add_argument('--dir', type=str, help='dir', default=os.getcwd(), required=False)
args = parser.parse_args()

```