[Python-ideas] Fast sum() for non-numbers

[Sergey]

On Jul 18, 2013 Terry Reedy wrote:

>>>> [1] http://bugs.python.org/file30917/fasttuple.py
>>>
>>> I do not like that implementation, because it shares the underlying
>>> storage. This means that tuples which ought to be small will grow and
>>> grow and grow just because you have called __add__ on a different tuple.
>>>
>>> Using Python 2.7 and your implementation above:
>>>
>>> py> a = ft([])  # empty tuple
>>> py> len(a._store)
>>> 0
>>> py> b = ft([1])
>>> py> c = a + b
>>> py> d = ft([2]*10000)
>>> py> c = c + d
>>> py> len(a._store)
>>> 10001
>>>
>>> So adding a big tuple to c changes the internal storage of a.
>>
>> Yes, that's right. All 3 variables `a`, `b` and `c` share the same
>> storage, so you effectively get 3 variables for the price of one. :)
>> That's the concept. Why is that bad?
> 
> What happens to len(a._store) after del c?

In that proof-of-concept implementation? Nothing. I tried to keep
it simple, so that the idea was easier to understand.

Its technically possible to have __del__ resizing internal store,
but is it really needed?

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