Using Python’s argparse for a “turn on”/”turn off” argument

What’s argparse ?

Argparse is a Python standard module and “makes it easy to write user-friendly command-line interfaces”. The 2.x doco is here, the 3.x doco is here. Before 2.7 there was the optparse module supplied as part of Python but that’s been deprecated and replaced with argparse.

“turn off” / “turn off” type arguments

I was working on some code yesterday and I wanted an argument of the “turn on” / “turn off” type. So for instance you might want the output to be verbose or not, it’s not uncommon to see this implemented by means of a


argument. When ‘–verbose’ is present the programmer provides verbose output, when it’s absent they don’t.

How then ?

A nice neat way to do this is to make use of the `action` (2.x and 3.x) argument of the `add_argument` method and to combine that with use of the `set_defaults` method so that a value is set in the case when the argument is not used by the user.

Here’s an example taken from my django-row-count project :

parser.add_argument('--echotostdout', dest='echotostdout', action='store_true')
args = parser.parse_args()

In this case a command line argument …


… sets an attribute


… to True if it’s present as an argument on the command line and to False if it’s absent.

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