[Python-Dev] argparse ugliness

David Stanek dstanek at dstanek.com
Mon Mar 8 17:55:09 CET 2010

On Mon, Mar 8, 2010 at 11:49 AM, Xavier Morel <python-dev at masklinn.net> wrote:
> On 8 Mar 2010, at 16:53 , David Stanek wrote:
>> On Mon, Mar 8, 2010 at 10:40 AM, Steven Bethard
>> <steven.bethard at gmail.com> wrote:
>>> In argparse, unlike optparse, actions are actually defined by objects
>>> with a particular API, and the string is just a shorthand for
>>> referring to that. So:
>>>  parser.add_argument ('--plot', action='store_true')
>>> is equivalent to:
>>>  parser.add_argument('--plot', argparse._StoreTrueAction)
>>> Because the names are so long and you'd have to import them, I've left
>>> them as private attributes of the module, but if there's really
>>> demand, we could rename them to argparse.StoreTrueAction, etc.
>> Any reason not to do something like:
>>  from argparse import actions
>>  ...
>>  parser.add_argument('--plot', actions.store_true)
>> Basically a small namespace for the constants.
> action is taken from **kwargs, not from a positional argument as *args
> is a sequence of option strings (so you can write
>  add_argument('-p', '/p', '--plot', '--land-mass')). So you'd have to write
> add_argument('--plot', action=actions.store_true) which is straight from
> the department of redundant redundancies.
> An option would be
>  parser.add(actions.StoreTrue('--plot'))
> but I'm not sure this makes any sense API-wise, and it would probably make
> the code a lot messier as the parser would have to reach into the action
> to get the information it needs. Either that, or the action would be an *arg
> and argparse would have to walk all of its *args type-testing each one to find
> if there's an action anywhere.

You could just change my example to:
  from argparse.actions import store_true
  parser.add_argument('--plot', action=store_true)

I would probably still import the actions namespace directly, but
wouldn't have to.

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