functions, list, default parameters

[Robert Kern]

On 2010-11-01 22:31 , Lawrence D'Oliveiro wrote:
> In message<8j1seqFa1eU2 at mid.individual.net>, Gregory Ewing wrote:
>
>> Steven D'Aprano wrote:
>>
>>> And how does Python know whether some arbitrary default object is mutable
>>> or not?
>>
>> It doesn't, that's the whole point.
>
> Of course it knows. It is the one defining the concept in the first place,
> after all.

No, the Python interpreter doesn't define the concept. The Python language 
developers did. "Immutable objects" are just those without an obvious API for 
modifying them. With various trickeries, I can mutate any immutable object. The 
Python interpreter doesn't know what's an "obvious API" and what isn't. It's a 
reasonably vague concept that doesn't have an algorithmic formulation.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco