[Python-Dev] [NPERS] Re: a feature i'd like to see in python #2: indexing of match objects (original) (raw)

Talin talin at acm.org
Thu Dec 7 19:24:02 CET 2006

Fredrik Lundh wrote:

Talin wrote:

Maybe instead of considering a match object to be a sequence, a match object should be considered a map? sure, except for one small thing. from earlier in this thread: > Ka-Ping Yee wrote: > >> I'd say, don't pretend m is a sequence. Pretend it's a mapping. >> Then the conceptual issues go away. to which I replied: > almost; that would mean returning KeyError instead of IndexError for > groups that don't exist, which means that the common pattern > > a, b, c = m.groups() > > cannot be rewritten as > > , a, b, c = m > > which would, perhaps, be a bit unfortunate.

I think the confusion lies between the difference between 'group' (which takes either an integer or string argument, and behaves like a map), and 'groups' (which returns a tuple of the numbered arguments, and behaves like a sequence.)

The original proposal was to make m[n] a synonym for m.group(n). "group()" is clearly map-like in its behavior.

It seems to me that there's exactly three choices:

-- Match objects behave like 'group' -- Match objects behave like 'groups' -- Match objects behave like 'group' some of the time, and like 'groups' some of the time, depending on how you refer to it.

In case 1, a match object is clearly a map; In case 2, it's clearly a sequence; In case 3, it's neither, and all talk of consistency with either map or sequence is irrelevant.

-- Talin

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