On 06/09/2013 10:13 PM, Alexander Belopolsky wrote:
On Sun, May 19, 2013 at 1:47 AM, Guido van Rossum <[email protected]
<mailto:[email protected]>> wrote:
I'm slow at warming up to the idea. My main concern is speed -- since
most code doesn't need it and function calls are already slow (and
obviously very common :-) it would be a shame if this slowed down
function calls that don't need it noticeably.
And we could remove this bit from the docs...
"""
The OrderedDict constructor and update() method both accept keyword
arguments, but their order is lost because Python’s function call semantics
pass-in keyword arguments using a regular unordered dictionary.
"""
Here is an idea that will not affect functions that don't need to know the
order of keywords: a special __kworder__ local variable. The use of this
variable inside the function will signal compiler to generate additional
bytecode to copy keyword names from the stack to a tuple and save it in
__kworder__.
I like the idea of an ordered dict acting the same as a regular dict with
an optional way to access order. It also will catch uses of unordered
dicts in situations where an ordered dict is expected by having the ordered
key words accessed in a way that isn't available in unordered dicts.
I don't care for a magic local variable inside of a function.
With that feature, an OrderedDict constructor, for example
can be written as
>
def odict(**kwargs):
return OrderedDict([(key, kwargs[key]) for key in __kworder__])
There is two situations where this would matter... The packing of
arguments when **kwargs is used in the function definition, and the
unpacking of arguments when **kwargs is used in the function call.
By having the unpackng side also work with ordered dicts, maybe we could
then replace the many *very common* occurrences of (*args, **kwargs) with
just (**all_args) or (***all_args). :)
It's the unordered nature of dictionaries that requires *args to be used
along with **kwargs when forwarding function arguments to other functions.
Another variation of this is to have a way to forward a functions
"signature name space" to another function directly and bypass the
signature parsing those cases.
Cheers,
Ron
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