[Python-Dev] A new dictionary implementation

[Alex]

Guido van Rossum <guido <at> python.org> writes:

> Hey, I like this! It's a subtle encouragement for developers to
> initialize all their instance variables in their __init__ or __new__
> method, with a (modest) performance improvement for a carrot. (Though
> I have to admit I have no idea how you do it. Wouldn't the set of dict
> keys be different while __init__ is in the middle of setting the
> instance variables?)
> 
> Another question: a common pattern is to use (immutable) class
> variables as default values for instance variables, and only set the
> instance variables once they need to be different. Does such a class
> benefit from your improvement?
> 
> > -- HansM
> 


While I absolutely cannot speak to this implementation. Traditionally this type
of approach is refered to as maps, and was pioneered in SELF, originally
presented at OOPSLA '89: http://dl.acm.org/citation.cfm?id=74884 .  PyPy also
uses these maps to back it's object, although from what I've read the
implementation looks nothing like the proposed one for CPython, you can read
about that here: http://bit.ly/zwlOkV , and if you're really excited about this
you can read our implementation here:
https://bitbucket.org/pypy/pypy/src/default/pypy/objspace/std/mapdict.py .

Alex