[Python-ideas] checking for identity before comparing built-in objects

[MRAB]

On 2012-10-04 16:53, Steven D'Aprano wrote:
> On 05/10/12 01:08, Victor Stinner wrote:
>> 2012/10/4 Steven D'Aprano<steve at pearwood.info>:
>>> On 04/10/12 21:48, Max Moroz wrote:
>>>>
>>>> It seems that built-in classes do not short-circuit `__eq__` method
>>>> when the objects are identical, at least in CPython:
>>>>
>>>>       f = frozenset(range(200000000))
>>>>       f1 = f
>>>>       f1 == f # this operation will take about 1 sec on my machine
>>>
>>>
>>> You shouldn't over-generalize. Some built-ins do short-circuit __eq__
>>> when the objects are identical. I believe that strings and ints both
>>> do. Other types might not.
>>
>> This optimization is not implemented for Unicode strings.
>
> That does not match my experience. In Python 3.2, I generate a large
> unicode string, and an equal but not identical copy:
>
> s = "aЖcdef"*100000
> t = "a" + s[1:]
> assert s is not t and s == t
>
>
> Using timeit, s == s is about 10000 times faster than s == t.
>
In Python 3.3 I get a similar result.