On 14/03/2012 13:30, Roy Smith wrote:
In article<87399bgw18....@benfinney.id.au>,
Ben Finney<ben+pyt...@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).
In other words, if there's a default but no explicit type, then the
type is the type of the default.
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.
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