On Tue, 19 Mar 2019 at 23:13, David Mertz <me...@gnosis.cx> wrote: > In a way, this case makes bugs worse because they are not only a Python > internal matter. XML is used to communicate among many tools and > programming languages, and relying on assumptions those other tools will > not follow us a bad habit. >
I have a recent example I encountered where the 3.7 behaviour (sorting attributes) results in a third-party tool behaving incorrectly, whereas maintaining attribute order works correctly. The particular case was using HTML <meta> tags for importing into Calibre for converting to an ebook. The most common symptom was that series indexes were sometimes being correctly imported, and sometimes not. Occasionally other <meta> tags would also fail to be correctly imported. Turns out that <meta name="series_index" content="3"/> gave consistently correct results, whilst <meta content="3" name="series_index"/> was erratic. And whilst I'd specified the <meta> tags with the name attribute first, I was then passing the HTML through BeautifulSoup, which sorted the attributes. Now Calibre is definitely in the wrong here - it should be able to import regardless of the order of attributes. But the fact is that there are a lot of tools out there that are semi-broken in a similar manner. This to me is an argument to default to maintaining order, but provide a way for the caller to control the order of attributes when formatting e.g. pass an ordering function. If you want sorted attributes, pass the built-in sorted function as your ordering function. But I think that's getting beyond the scope of this discussion. Tim Delaney
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