argparse

argparse is a python library for creating command line interfaces and parsing command line arguments.

argparse creates an object that matches the different input fields defined for your command line interface, these fields are populated from the data submitted by a user or are assigned as defaults, or otherwise unused. In the example below, we define a CLI that has an optional flag --message, this value defaults to hello (but can be set by the user) and is placed on the destination object when parse_args is called (in this case args) and can be accessed by a field of the same name on the object called message.

#cli.py
import argparse

parser = argparse.ArgumentParser()
parser.add_argument("--message", default="hello", dest="message")

args = parser.parse_args()

print(args.message)

If this is called with no arguments the default value is used:

$ python3 cli.py
$ hello

If this is called with arguments then the value passed in after the flag is used:

$ python3 cli.py --message Greetings
$ Greetings

You can create optional arguments by prefacing argument names with a - hyphen or -- double hyphen. You can give an argument multiple flag names by comma separating a list of names.

parser.add_argument("--message", "-m")

Action

The action argument describes what action should be taken on a particular argument.

You can set configuration flags by using the store_true and store_false actions.