[Python-Dev] Tuples vs. lists

[Aahz Maruch]

Guido van Rossum wrote:
> Aahz:
>>
>> Sure, but then I can't just copy references to the tuple when creating a
>> copy of an instance, I'd have to copy the entire list.  That's what I
>> meant by efficiency.  There are important semantic differences coming
>> from the fact that tuples are immutable and lists are mutable, and I
>> think that a strict heterogeneous/homogenous distinction loses that.
> 
> Well, as long as you promise not to change it, you *can* copy a
> reference, right?  I guess I don't understand your application
> enough -- do you intend this to be a starting point that is modified
> during the program's execution, or is this a constant array?

It's a constant.  The BCD module is Binary Coded Decimal; instances are
intended to be as immutable as strings and numbers (well, it *is* a
number type).  Modifying an instance is guaranteed to produce a new
instance.  To a large extent, I guess I feel that if a class is intended
to be immutable, each of its underlying data attributes should also be
immutable.
-- 
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