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From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: flaming vs accuracy [was Re: Performance of int/long in Python 3]
Date: Thu, 28 Mar 2013 12:01:25 -0400
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Xref: csiph.com comp.lang.python:42160

On 3/28/2013 10:38 AM, Chris Angelico wrote:

> PEP393 strings have two optimizations, or kinda three:
>
> 1a) ASCII-only strings
> 1b) Latin1-only strings
> 2) BMP-only strings
> 3) Everything else
>
> Options 1a and 1b are almost identical - I'm not sure what the detail
> is, but there's something flagging those strings that fit inside seven
> bits. (Something to do with optimizing encodings later?)

Yes. 'Encoding' an ascii-only string to any ascii-compatible encoding 
amounts to a simple copy of the internal bytes. I do not know if *all* 
the codecs for such encodings are 393-aware, but I do know that the 
utf-8 and latin-1 group are. This is one operation that 3.3+ does much 
faster than 3.2-


-- 
Terry Jan Reedy