Are dicts supposed to raise comparison errors

[Chris Angelico]

On Wed, Aug 1, 2018 at 7:43 PM, Robin Becker <robin at reportlab.com> wrote:
> On 01/08/2018 09:52, Chris Angelico wrote:
>>
>> On Wed, Aug 1, 2018 at 6:36 PM, Robin Becker <robin at 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.
>

I'm not sure how you're interpreting the word 'or' in my explanation,
but it has the same meaning it has in Python code.

ChrisA