[Python-ideas] Ordered storage of keyword arguments

M.-A. Lemburg mal at egenix.com
Thu Oct 28 10:13:09 CEST 2010

Chris Rose wrote:
> I'd like to resurrect a discussion that went on a little over a year
> ago [1] started by Michael Foord suggesting that it'd be nice if
> keyword arguments' storage was implemented as an ordered dict as
> opposed to the current unordered form.
> I'm interested in picking this up for implementation, which presumably
> will require moving the implementation of the existing ordereddict
> class into the C library.
> Are there any issues that this might cause in implementation on the
> py3k development line?
> [1] http://mail.python.org/pipermail/python-ideas/2009-April/004163.html

Ordered dicts are a lot slower than normal dictionaries. I don't
think that we can make such a change unless we want to make
Python a lot slower at the same time.

If you only want to learn about the definition order of the
keywords you can use the inspect module.

>>> def f(a,b,c=1,d=2): pass
>>> inspect.getargspec(f)
(['a', 'b', 'c', 'd'], None, None, (1, 2))

I don't see much use in having the order of providing the
keyword arguments in a function call always available.
Perhaps there's a way to have this optionally, i.e. by
allowing odicts to be passed in as keyword argument dict ?!

Where I do see a real use is making the order of class
attribute and method definition accessible in Python
(without having to use meta-class hacks like e.g. Django's
ORM does).

It would then be must easier to use classes to represent
external resources that rely on order, e.g. database table
schemas or XML schemas.

Classes are created using a keyword-like dictionary as
well, so the situation is similar. The major difference
is that classes aren't created as often as functions are

Marc-Andre Lemburg

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