[Python-Dev] Using PEP384 Stable ABI for the lzma extension module (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Tue Oct 4 21:33:34 CEST 2011

Am 04.10.11 21:06, schrieb Amaury Forgeot d'Arc:

2011/10/4 "Martin v. Löwis"<martin at v.loewis.de>:

- PyBytesResize() is missing; I moved it under a PyLIMITEDAPI section. ??? Are you proposing to add PyBytesResize to the PyLIMITEDAPI set of functions? It's not even an API function in the first place (it starts with an underscore), so how can it be a limited API function? It's not a proposal of any kind; it's just the workaround I used to compile and test. OTOH, it seems that many modules already use this function. Is there another method that does not need to copy data?

Not sure what you are using it for. If you need to extend the buffer in case it is too small, there is absolutely no way this could work without copies in the general case because of how computers use address space. Even _PyBytes_Resize will copy the data.

The only way to avoid copying is to run over the input twice: once to determine how large the output will have to be, and then another time to actually produce the output. Whether or not that's actually faster than copying the output depends on how much work this size computation requires. It would be nice if LZMA had "output size" information embedded in it, but it may not.

Regards, Martin

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