[Python-Dev] RFC: Add a new builtin strarray type to Python?

[Hrvoje Niksic]

On 10/02/2011 06:34 PM, Alex Gaynor wrote:
> There are a number of issues that are being conflated by this thread.
>
> 1) Should str += str be fast. In my opinion, the answer is an obvious and
>     resounding no. Strings are immutable, thus repeated string addition is
>     O(n**2). This is a natural and obvious conclusion. Attempts to change this
>     are only truly possible on CPython, and thus create a worse enviroment for
>     other Pythons, as well as a quite misleading, as they'll be extremely
>     brittle. It's worth noting that, to my knowledge, JVMs haven't attempted
>     hacks like this.

CPython is already misleading and ahead of JVM, because the str += str 
optimization has been applied to Python 2 some years ago - see
http://hg.python.org/cpython-fullhistory/rev/fb6ffd290cfb?revcount=480

I like Python's immutable strings and consider it a good default for 
strings.  Nevertheless a mutable string would be useful for those 
situations when you know you are about to manipulate a string-like 
object a number of times, where immutable strings require too many 
allocations.

I don't think Python needs a StringBuilder - constructing strings using 
a list of strings or StringIO is well-known and easy.  Mutable strings 
are useful for the cases where StringBuilder doesn't suffice because you 
need modifications other than appends.  This is analogous to file writes 
- in practice most of them are appends, but sometimes you also need to 
be able to seek and write stuff in the middle.

Hrvoje