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Re: Enchancement suggestion for argparse: intuit type from default

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On 3/15/12 5:59 AM, Cameron Simpson wrote:
> On 15Mar2012 12:22, Ben Finney<ben+python@benfinney.id.au>  wrote:
> | Roy Smith<roy@panix.com>  writes:
> |>  I'll admit I hadn't considered that, but I don't see it as a major
> |>  problem. The type intuition could be designed to only work for types
> |>  other than NoneType.
> |
> | −1, then. It's growing too many special cases, and is no longer simple
> | to describe, so that indicates it's probably a bad idea.
>
> If `type` is not supplied and `default` is present and not None, `type`
> shall be the type of `default`.
>
> That seems straightforward to me. It's a single sentence, easy to read
> and understand, and potentially saves a lot of code verbiage (gratuitous
> type= prarameters). I say "gratuitous" because unless `default` is a
> sentinel for "no option supplied", the `type` should always match
> type(default). Or am I wrong about that?

Yes. Not all type(default) types can be called with a string to produce a valid 
value. Note that "type=" is really a misnomer. argparse doesn't really want a 
type object there; it wants a converter function that takes a string to an object.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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Enchancement suggestion for argparse: intuit type from default roy@panix.com (Roy Smith) - 2012-03-13 17:08 -0400
  Re: Enchancement suggestion for argparse: intuit type from default Ben Finney <ben+python@benfinney.id.au> - 2012-03-14 08:35 +1100
    Re: Enchancement suggestion for argparse: intuit type from default Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-14 12:53 +0000
      Re: Enchancement suggestion for argparse: intuit type from default Ben Finney <ben+python@benfinney.id.au> - 2012-03-15 00:19 +1100
        Re: Enchancement suggestion for argparse: intuit type from default Roy Smith <roy@panix.com> - 2012-03-14 09:30 -0400
          Re: Enchancement suggestion for argparse: intuit type from default MRAB <python@mrabarnett.plus.com> - 2012-03-14 17:26 +0000
          Re: Enchancement suggestion for argparse: intuit type from default Ian Kelly <ian.g.kelly@gmail.com> - 2012-03-14 13:03 -0600
  Re: Enchancement suggestion for argparse: intuit type from default rusi <rustompmody@gmail.com> - 2012-03-14 03:22 -0700
  Re: Enchancement suggestion for argparse: intuit type from default Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-03-14 13:26 +0100
  Re: Enchancement suggestion for argparse: intuit type from default John Nagle <nagle@animats.com> - 2012-03-14 16:32 -0700
    Re: Enchancement suggestion for argparse: intuit type from default Roy Smith <roy@panix.com> - 2012-03-14 20:52 -0400
      Re: Enchancement suggestion for argparse: intuit type from default Ben Finney <ben+python@benfinney.id.au> - 2012-03-15 12:22 +1100
        Re: Enchancement suggestion for argparse: intuit type from default Cameron Simpson <cs@zip.com.au> - 2012-03-15 16:59 +1100
        Re: Enchancement suggestion for argparse: intuit type from default Robert Kern <robert.kern@gmail.com> - 2012-03-15 10:06 +0000
          Re: Enchancement suggestion for argparse: intuit type from default Roy Smith <roy@panix.com> - 2012-03-15 09:28 -0400
            Re: Enchancement suggestion for argparse: intuit type from default Cameron Simpson <cs@zip.com.au> - 2012-03-16 08:18 +1100
      Re: Enchancement suggestion for argparse: intuit type from default MRAB <python@mrabarnett.plus.com> - 2012-03-15 02:10 +0000

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