[Python-Dev] argparse ambiguity handling (original) (raw)

Eric Smith eric at trueblade.com
Wed Apr 21 09:53:16 CEST 2010

Cameron Simpson wrote:

On 20Apr2010 15:27, Neal Becker <ndbecker2 at gmail.com> wrote: | Steven Bethard wrote: | | > On Tue, Apr 20, 2010 at 11:55 AM, Neal Becker <ndbecker2 at gmail.com> wrote: | >> I've noticed argparse ambiguity handling has changed a bit over last few | >> revisions. | >> | >> I have cases where 1 valid input is a prefix of another: | >> | >> e.g.: | >> '--string' | >> '--string2' | >> | >> With the most recent 1.1, the behavior is: | >> | >> --string=hello | >> | >> is accepted, while: | >> | >> --strin=hello | >> | >> is marked as ambiguous. | >> | >> I'm OK with this, but just want to know if there is agreement that this | >> is the behavior we want. | > | > I don't have a strong feeling about this. What was the behavior before? | > Steve | | At least 1 earlier version said that even exact match was ambiguous. | | I have a preference to allow at least exact matches to succeed even in the | case of ambiguity - mainly because I accidentally created this already once, | and I feel it's better to at least work somewhat. Not sure if there is any | more elegant solution. OTOH, I feel this is somewhat inelegant, as it | appears to treat exact match as a special case.

I think the new behaviour is desirable. Plenty of commands have both --foo and --foo-tweak. Usually because --foo came first and --foo-tweak came later, or simply because --foo is the simple and obvious and commonly wanted mode and --foo-tweak is a special case. Real world example: rsync and the --delete* options. I'm sure plenty of others can be found. The new behaviour makes this doable. The old behaviour made it unimplementable. Maybe it is desirable to be able to forbid this arguably-ambiguous option set, but I definitely feel that the current behaviour should be available.

I agree the new behavior is desirable. And I also think it should be the default, although I feel less strongly about that.

But since this behavior seems to be an accident of the implementation (based on Steve's comment above), I think a test should be added for it if it's accepted as a Good Thing (tm). Otherwise it's possible that it will vanish as the implementation changes.

Eric.

More information about the Python-Dev mailing list