[Python-Dev] The "lazy strings" patch [was: PATCH submitted: Speed up + for string concatenation, now as fast as "".join(x) idiom]

["Martin v. Löwis"]

Larry Hastings schrieb:
> I've significantly enhanced my string-concatenation patch, to the point
> where that name is no longer accurate.  So I've redubbed it the "lazy
> strings" patch.

It's not clear to me what you want to achieve with these patches,
in particular, whether you want to see them integrated into Python or
not.

> The major new feature is that string *slices* are also represented with
> a lazy-evaluation placeholder for the actual string, just as
> concatenated strings were in my original patch.  The lazy slice object
> stores a reference to the original PyStringObject * it is sliced from,
> and the desired start and stop slice markers.  (It only supports step =
> 1.)

I think this specific approach will find strong resistance. It has been
implemented many times, e.g. (apparently) in NextStep's NSString, and
in Java's string type (where a string holds a reference to a character
array, a start index, and an end index). Most recently, it was discussed
under the name "string view" on the Py3k list, see

http://mail.python.org/pipermail/python-3000/2006-August/003282.html

Traditionally, the biggest objection is that even small strings may
consume insane amounts of memory.

> Its ob_sval is NULL until the string is rendered--but that rarely
> happens!  Not only does this mean string slices are faster, but I bet
> this generally reduces overall memory usage for slices too.

Channeling Guido: what real-world applications did you study with
this patch to make such a claim?

> I'm ready to post the patch.  However, as a result of this work, the
> description on the original patch page is really no longer accurate:
>    
> http://sourceforge.net/tracker/index.php?func=detail&aid=1569040&group_id=5470&atid=305470
> Shall I close/delete that patch and submit a new patch with a more
> modern description?  After all, there's not a lot of activity on the old
> patch page...

Closing the issue and opening a new is fine.

Regards,
Martin