Enchancement suggestion for argparse: intuit type from default

[Roy Smith]

In article <87399bgw18.fsf at benfinney.id.au>,
 Ben Finney <ben+python at benfinney.id.au> wrote:

> Right. I dislike proposals for run-time type inference in Python, since
> they are too magical.
> 
> Especially since we're talking about user input (arguments from the
> command line to the program); that requires more explicit declarations
> and checking, not less.
> 
> > What if you want an argument --foo that will accept arbitrary types? Then 
> > you would need some way to tell argparse not to infer the type from the 
> > default.
> 
> So we would then need to special-case the special-case? Even more reason
> to dislike this proposal.
> 
> > Explicit declarations should be used only for the uncommon cases where
> > type inference cannot cope.
> 
> That's our point of disagreement, then: I think explicit declarations
> should be required regarding user input.

I wasn't suggesting that the type be inferred from what the user 
entered.  I was suggesting it be inferred from what the programmer had 
done (i.e. what value they had given the 'default' parameter).

It's already inferred that the type is a string if you don't give it any 
value.  What possible meaning could:

parser.add_argument('--foo', default=100)

have?  If I run the program with:

$ prog

then foo defaults to the integer 100, but if I run it with:

$ prog --foo=100

then I get the string "100"?  Surely there's not much of a use case for 
that.