[Python-Dev] RFD: how to build strings from lots of slices?

[Fredrik Lundh]

Ka-Ping Yee wrote:
> > 1. introduce a PySliceListObject, which behaves like a
> > simple sequence of strings, but stores them as slices.
>=20
> It occurred to me when i read this that *all* slices
> could be references within the original string, since
> strings are immutable.  That is,
>=20
>     s[x:y]
>=20
> could return a PyStringRefObject that behaves just like
> a string, but contains a length y - x and a pointer to
> &(s->ob_sval) + x instead of the character data itself.
> The creation of this PyStringRefObject would increment
> the reference count of s by 1.
>=20
> Perhaps this has been suggested before.

as an experiment, I actually implemented this for the
original unicode string type (where "split" and "slice"
returned slice references, not string copies).

here are some arguments against it:

a) bad memory behaviour if you slice small strings out
of huge input strings -- which may surprise newbies.

b) harder to interface to underlying C libraries -- the
current string implementation guarantees that a Python
string is also a C string (with a trailing null).

personally, I don't care much about (a) (e.g. match
objects already keep references to the input string,
and if this is a real problem, you can always use a
more elaborate data structure...).

(b) is a bit harder to ignore, though.

</F>