[issue25709] Problem with string concatenation and utf-8 cache.

[Steven D'Aprano]

Steven D'Aprano added the comment:

On Mon, Nov 23, 2015 at 09:48:46PM +0000, STINNER Victor wrote:

> * the string has a cached UTF-8 byte string (ex: int(s) was called before the resize)

Why do strings cache their UTF-8 encoding?

I presume that some of Python's internals rely on the UTF-8 encoding 
rather than the internal Latin-1/UCS-2/UTF-32 representation (PEP 393). 
E.g. I infer from the above that int(s) parses the UTF-8 representation 
of s rather than the internal representation. Is that right?

Nevertheless, I wonder why the UTF-8 representation is cached. Is it 
that expensive to generate that it can't be done on the fly, as needed? 
As it stands now, non-ASCII strings may be up to twice as big as they 
need be, once you include the UTF-8 cache. And, as this bug painfully 
shows, the problem with caches is that you run the risk of the cache 
being out of date.

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<http://bugs.python.org/issue25709>
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