Using positional arguments from argparse as function name

Question

I have set up a script with argparse that gives me the following NameSpace:

Namespace(action='list', input='all', target='domain')

I have made a few functions which are called according to the positionals, and at the moment I have a working situation by calling them with blurbs of code like this one:

if args.action == 'list':
    if len(sys.argv) == 2:
        parser.print_help()
        sys.exit(0)
elif args.target == 'domain':
    domain_list()
elif args.target == 'forwarding':
    forwarding_list()
elif args.target == 'transport':
    transport_list()
elif args.target == 'user':
    user_list()
else:
    all_list()

I know this can be done way, way better than this; but with my limited knowledge of Python, I can't seem to figure this one out.

Recap: I want something like, if at all possible (pseudocode)

if args.action == 'add':
    target = args.target
    target_add()

where target_add() is something like domain_add().

Thanks in advance!

Would something like this help? http://stackoverflow.com/questions/3061/calling-a-function-from-a-string-with-the-functions-name-in-python — favoretti, Dec 31 '12 at 13:11
You may be interested in [docopt](https://github.com/docopt/docopt), it is "argparse for humans". — Paulo Scardine, Dec 31 '12 at 13:20
@favoretti; yeah, as far as I can see this is much like the accepted answer to this question :) @PauloScardine I understand argparse after reading a lot of the documentation and lots of questions about it on stackoverflow :), however, I got stuck with on the inner workings of python-code itself ^_^ — Peter van Arkel, Dec 31 '12 at 14:23

unutbu · Accepted Answer · 2012-12-31T13:50:36.233

It sounds like action could be list or add, while target could be domain, forwarding, transport, or user. Yes, you would end up with a lot of if..then..else code if you had to manually list what each combination of options would do.

Here is a way to simplify this:

Use itertools.product to generate all the possible combinations of options.
Use a whitelist dispatch dict to map options to functions. The keys are 2-tuples, such as ('domain','list'), or ('transport','add'). The values are the associated function objects.

import itertools as IT

targets = 'domain forwarding transport user'.split()
actions = 'list add'.split()

dispatch = {key:globals()['%s_%s' % key] for key in IT.product(targets, actions)}

# This calls the function specified by (target, action).
# The `dict.get` method is used so that if the key is not in `dispatch`, the `all_list` function is called.
dispatch.get((args.target, args.action), all_list)()

Awesome, this works like a charm for me and has also cut my code in half! :) — Peter van Arkel, Dec 31 '12 at 14:19

Using positional arguments from argparse as function name

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