On 22Oct2018 1007, Serhiy Storchaka wrote: > 22.10.18 16:24, Steve Dower пише: >> Yes, that's true. But "should reduce ... footprint" is also an >> optimisation that deserves a benchmark by that standard. Also, I'm >> proposing keeping the 'kind' as UCS-2 when the string is created from >> UCS-2 data that is likely to be used as UCS-2. We would not create the >> UCS-1 version in this case, so it's not the same as prefilling the >> cache, but it would cost a bit of memory in exchange for CPU. If >> slicing and concatentation between matching kinds also preserved the >> kind, a lot of path handling code could avoid back-and-forth conversions. > > Oh, I afraid this will complicate the whole code of unicodeobject.c (and > several other files) a much and can introduce a lot of subtle bugs. > > For example, when you search a UCS2 string in a UCS1 string, the current > code returns the result fast, because a UCS1 string can't contain codes > > 0xff, and a UCS2 string should contain codes > 0xff. And there are > many such assumptions. That doesn't change though, as we're only ever expanding the range. So searching a UCS2 string in a UCS2 string that doesn't contain any actual UCS2 characters is the only case that would be affected, and whether that case occurs more than the UCS2->UCS1->UCS2 conversion case is something we can measure (but I'd be surprised if substring searches occur more frequently than OS conversions). Currently, unicode_compare_eq exits early when the kinds do not match, and that would be a problem (but is also easily fixable). But other string operations already handle mismatched kinds. Cheers, Steve
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