[Python-3000] Detecting conflicts in dict displays

[Aaron Bingham]

Fredrik Lundh wrote:

>Guido van Rossum wrote:
>
>  
>
>>>Wouldn't the behavior of the above be undefined for the case where a ==
>>>b?  I'd much rather get an exception than undefined behavior.
>>>      
>>>
>>There's nothing undefined in the language currently about {a: 1, b:
>>2}. It creates an empty dict d, and then does d[a] = 1; d[b] = 2. If a
>>and b are equal, you end up with {a: 2}.
>>    
>>
>
>for the formal definition, see "dictionary displays" in the language reference:
>
>    The key/datum pairs are evaluated from left to right to define the
>    entries of the dictionary: each key object is used as a key into the
>    dictionary to store the corresponding datum. /.../
>
>    Clashes between duplicate keys are not detected; the last datum
>    (textually rightmost in the display) stored for a given key value pre-
>    vails.
>
>    ( http://pyref.infogami.com/dictionary-displays )
>  
>
Thanks for the clarification.  That is reassuring.  Of course, this may 
not do what was intended under certain circumstances, but at least the 
behavior is well defined.

Regards,

-- 
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Aaron Bingham
Senior Software Engineer
Cenix BioScience GmbH
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