[issue10581] Review and document string format accepted in numeric data type constructors

[Marc-Andre Lemburg]

Marc-Andre Lemburg added the comment:

On 14.06.2013 03:43, Alexander Belopolsky wrote:
> 
> Alexander Belopolsky added the comment:
> 
> PEP 393 implementation has already added the fast path to decimal encoding:
> 
> http://hg.python.org/cpython/diff/8beaa9a37387/Objects/unicodeobject.c#l1.3735
> 
> What we can do, however, is improve performance of converting non-ascii numerals by looking up only the first digit's value and converting the rest using simple:
> 
> value = code - (first_code - first_value)
> if not 0 <= value < 10:
>    raise or fall back to UCD lookup

I'm not sure whether just relying on PEP 393 is good enough.

Of course, you can special case the conversion based on the
kind, but that's only one form of optimization.

Slicing operations don't recheck the max code point
used in the substring. As a result, a slice may very well
be of the UCS2 kind, even though the text itself is ASCII.

Apart from the fast-path based on the string kind,
I think the decimal encoder would also have to scan the
string for non-ASCII code points. If it finds non-ASCII
code points, it would have to call the normalizer and
restart the scan based on the normalized string.

-- 
Marc-Andre Lemburg
eGenix.com

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<http://bugs.python.org/issue10581>
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