On Sun, Jul 19, 2020 at 6:38 AM Marco Sulla
<[email protected]> wrote:
>
> On Sat, 18 Jul 2020 at 10:02, Inada Naoki <[email protected]> wrote:
>>
>> On Sat, Jul 18, 2020 at 7:05 AM Marco Sulla
>> <[email protected]> wrote:
>> > For what I know, CPython uses PyDictObject for kwargs. Since dicts are
>> > mutable, it's a problem to cache them properly.
>>
>> On caller side, Python doesn't use dict at all.
>> On callee side, dict is used for `**kwargs`. But changing it to frozendict
>> is
>> backward incompatible change.
>
>
> Not sure of what you mean with caller and callee. If you're talking about
> Python, I agree, kwargs must be dicts. But I was talking about CPython and
> PyDictObject, that is used internally for kwargs.
>
I am talking about CPython VM. Caller is code calling Python. Callee
is the function called.
Look at the caller side first:
# x.py
foo(a=1, b=2)
$ python3 -m dis x.py
1 0 LOAD_NAME 0 (foo)
2 LOAD_CONST 0 (1)
4 LOAD_CONST 1 (2)
6 LOAD_CONST 2 (('a', 'b'))
8 CALL_FUNCTION_KW 2
10 POP_TOP
12 LOAD_CONST 3 (None)
14 RETURN_VALUE
As you can see, dict is not created during calling a function.
On the other hand, if callee is defined as:
def foo(a, b): ...
CPython VM doesn't create a dict at all. If callee is defined as:
def foo(**kwargs): ...
The kwargs is dict, of course. And changing it to frozendict is not
backward compatible.
C function is similar. If the C function is defined using
METH_KEYWORDS, keyword
arguments are passed as dict. If the C function is defined using METH_FASTCALL,
keyword arguments are passed as C array.
> On Sat, 18 Jul 2020 at 10:02, Inada Naoki <[email protected]> wrote:
>>
>> Currently, `for k,v in d.items()`
>> doesn't create
>> temporary list or set-like.
>> I think using "real object" is not good performance optimization.
>
>
> Well, this is true... but they create view objects that are quite slow.
Is it really slow? It is just a thin wrapper object. How is it slow compared
iter(list)? Iterator is just a thin wrapper too.
Regards,
--
Inada Naoki <[email protected]>
--
https://mail.python.org/mailman/listinfo/python-list
