On 01/08/2018 09:52, Chris Angelico wrote:
On Wed, Aug 1, 2018 at 6:36 PM, Robin Becker <ro...@reportlab.com> wrote:
On 31/07/2018 16:52, Chris Angelico wrote:
..........
it says explicitly that numeric keys will use numeric comparison, but no
.........
Technically, the comparison used is:
a is b or a == b
in other words, identity will match, but mainly, equality is used. The
identity check improves performance in many common cases, and also
avoids pathological cases involving float("nan"), but in general
discussion, it's assumed that value rather than identity is the
comparison used.
ChrisA
If the testing were done in that order then no comparison warning would occur
as inspection shows 'a' is not b'a'
> C:\code\hg-repos\reportlab\tmp>\python37\python.exe -b -Wall
Python 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:59:51) [MSC v.1914 64 bit
(AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
'a' is b'a'
False
so presumably the testing goes something like
a is b or (a==b if comparable(a,b) else False)
even so I still think errors/warnings created internally by implementers should not be exposed. It's not a big deal. I'm a bit
surprised that we don't have a mapping which uses only identity as that would be faster.
--
Robin Becker
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