test.py

#!/usr/bin/env python
"""Example of choices with begins.

Python code:
    main()
    main('bar')
    main(arg='baz')

Command line equivalent:
    test.py
    test.py --arg bar
    test.py --arg baz

Deficiencies:
    * main(Choices.bar) doesn't work
    * test.py -h doesn't show the choices
    * @begin.convert(_automatic=True) doesn't work
"""
# enum was introduced in Python 3.4
# For earlier versions, pip install enum34
from enum import Enum

import begin


# Enum values can be abused
class Choices(Enum):
    foo = 1
    bar = 2.0
    baz = '03'


# Choices must be accessed as Choices.foo or Choices['foo']
# Enums should be a special case so we can just use arg=Choices
@begin.start
@begin.convert(arg=Choices.__getitem__)
def main(arg=Choices.foo):
    # Up to you whether you care about the name or the value
    print('you chose Choices.{} -> {}'.format(arg.name, arg.value))