[Python-ideas] creating dicts with duplicates on purpose [was Re: dictionary constructor should not allow duplicate keys]

[Ethan Furman]

On 05/04/2016 07:54 AM, Paul Moore wrote:
> On 4 May 2016 at 13:42, Ethan Furman wrote:
>> On 05/04/2016 02:48 AM, Paul Moore wrote:

>>> The problem is that it could also break code that works at the moment.
>>> Consider a mapping of constants to names:
>>>
>>> colors = {
>>>       RED: "Red",
>>>       BLUE: "Blue",
>>>       PINK: "Pink",
>>>       LIGHT_BLUE: "Light Blue",
>>>       DARK_BLUE: "Dark Blue",
>>> }
>>>
>>> On a certain output device, there may be no "light blue", and in that
>>> case the code sets LIGHT_BLUE = BLUE. That's entirely reasonable, and
>>> the author may be perfectly happy with the current behavior in that
>>> case.
>>
>> Actually, that code is setting BLUE = "Light Blue".  ;)
>
> You missed my point, I think. BLUE and LIGHT_BLUE are "constant"
> values (set once at the top of the program).

No, I got your point, and I agree.  But one of us is confused about your 
explanation of that example (it could easily be me).  Here's how I think 
it works:

RED = 1
BLUE = 2
PINK = 3
LIGHT_BLUE = 4
DARK_BLUE = 5

# oops, light blue not supported on this machine, just use blue
LIGHT_BLUE = 2

 >>> colors = {
       RED: "Red",
       BLUE: "Blue",
       PINK: "Pink",
       LIGHT_BLUE: "Light Blue",
       DARK_BLUE: "Dark Blue",
      }

 >>> colors
{1: 'Red', 2: 'Light Blue', 3: 'Pink', 5: 'Dark Blue'}

So my issue was not with your point, but with your explanation of the 
example of your point.

--
~Ethan~