[Python-Dev] performance of {} versus dict(), de fmd(**kw): return kw trumps all ; -)

[Richard Oudkerk]

On 15/11/2012 4:21pm, Terry Reedy wrote:
> I was thinking that CPython could check the ref count of the input
> keyword dict to determine whether it is newly created and can be
> returned or is pre-existing and must be copied. But it seems not so.
>
>  >>> def d(**x): return sys.getrefcount(x)
>
>  >>> import sys
>  >>> d(a = 3)
> 2
>  >>> d(**{'a': 3})
> 2
>  >>> b = {'a': 3}
>  >>> d(**b)
> 2
>
> I was expecting 3 for the last one.

Isn't it always newly created?

     >>> def f(**x): return x
     ...
     >>> b = {'a':3}
     >>> b is f(**b)
     False

-- 
Richard