On Tue, Sep 13, 2016 at 5:25 PM, Antoon Pardon
<antoon.par...@rece.vub.ac.be> wrote:
> Op 12-09-16 om 23:29 schreef Chris Angelico:
>> On Tue, Sep 13, 2016 at 7:19 AM, BartC <b...@freeuk.com> wrote:
>>> By the same argument, then strings and ints are also mutable.
>>>
>>> Here, the original tuple that a refers to has been /replaced/ by a new one.
>>> The original is unchanged. (Unless, by some optimisation that recognises
>>> that there are no other references to it, the original is actually appended
>>> to. But in general, new objects are constructed when implementing +=.)
>> And by definition, that optimization cannot be detected. At best, all
>> you could do is something like:
>>
>> old_id = id(a)
>> a += something
>> if id(a) == old_id:
>> print("We may have an optimization, folks!")
>>
>> But that can have false positives. If two objects do not concurrently
>> exist, they're allowed to have the same ID number.
>
> You could do the following:
>
> old_a = a
> a += something
> if old_a is a:
> print("We have an optimization, folks!")
>
Uhm... that defeats the whole point of it being an optimization. See
above, "there are no other references to it". :)
If this condition is ever true, Python's language spec has been violated.
ChrisA
--
https://mail.python.org/mailman/listinfo/python-list
