Thanks for your very informative reply.
I replied you in issue41486. Maybe memory blocks will not bring performance
improvement to _PyBytesWriter/_PyUnicodeWriter, which is a bit frustrating.
> For a+b, Python first computes "a", then "b", and finally "a+b". I don't see
> how your API could opt
Some code needs to maintain an output buffer that has an unpredictable size.
Such as bz2/lzma/zlib modules, _PyBytesWriter/_PyUnicodeWriter.
In current code, when the output buffer grows, resizing will cause unnecessary
memcpy().
issue41486 uses memory blocks to represent output buffer in bz2/l
