[Python-Dev] folding cElementTree behind ElementTree in 3.3 (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Tue Feb 21 22:47:43 CET 2012

Am 21.02.2012 11:41, schrieb Eli Bendersky:

On Tue, Feb 21, 2012 at 03:59, Nick Coghlan <ncoghlan at gmail.com_ _<mailto:ncoghlan at gmail.com>> wrote: On Tue, Feb 21, 2012 at 11:39 AM, Eli Bendersky <eliben at gmail.com_ _<mailto:eliben at gmail.com>> wrote: > So the two choices here are either change the documentation or the C > implementation to actually make Element a class. The first is of course > simpler. However, someone somewhere may have written code that knowingly > forces the Python implementation to be used and subclasses Element. Such > code will break in 3.3, so it probably makes sense to invest in making > Element a class in the C implementation as well. Yeah, that's my take as well (especially since, in 3.2 and earlier, "forcing" use of the pure Python version was just a matter of importing ElementTree instead of cElementTree). I can't fathom why someone would do it though, since bar tiny differences (like this one) cET is just a faster ET and it's available practically everywhere with CPython. I mean, is it really important to be able to subclass ET.Element? What goal does it serve?

Statements like this make me extremely worried. Please try to adopt a position of much higher caution, accepting that a change is "incompatible" if there is a remote possibility that someone might actually rely on the original behavior. Otherwise, I predict that you will get flooded with complaints that you broke ET for no good reason.

In the specific case, I tried to write a script that determines the memory usage of ET. As Element is lacking gc.get_referents support, I tried isinstance(o, Element), which failed badly.

Feel free to dismiss this application as irrelevant, but I do wish that somebody was in charge of ET who was taking backwards compatibility as serious as Fredrik Lundh.

Regards, Martin

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