[Python-Dev] Very Strange Argument Handling Behavior

[Steve Holden]

Raymond Hettinger wrote:
> 
> On Apr 16, 2010, at 2:42 PM, Daniel Stutzbach wrote:
>>
>> IIRC, there's a performance hack in dictobject.c that keeps track of
>> whether all of the keys are strings or not.  The hack is designed so
>> that lookup operations can call the string compare/hash functions
>> directly if possible, rather than going through the slower PyObject_
>> functions.
>>
>> Consequently, validating **kwds should be cheap.
>>
> Good thinking.
> 
> That would definitely be better than scanning the full dict on every call.
> 
I'm sure we wouldn't want to go so far as to inhibit this. (Py 3.1)

>>> def f(**kwargs):
...   kwargs[1] = "dummy"
...   print(kwargs)
...
>>> f(this="Guido", that="Raymond", the_other="Steve")
{'this': 'Guido', 1: 'dummy', 'the_other': 'Steve', 'that': 'Raymond'}
>>>

Or would we? If it's OK to mutate kwargs inside the function to contain
a non-string key, why isn't it OK to pass a non-string key in?

I understand that it couldn't be generated using keyword argument
syntax, but I don't see why we discriminate against f(**dict(...)) to
limit it to what could be generated using keyword argument syntax. Is
this such a big deal?

regards
 Steve
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