[Python-Dev] A new dictionary implementation

[Yury Selivanov]

Hello Mark,

First, I've back-ported your patch on python 3.2.2 (which was relatively
easy).  Almost all tests pass, and those that don't are always failing on
my machine if I remember.  The patch can be found here: http://goo.gl/nSzzY

Then, I compared memory footprint of one of our applications (300,000 LOC) 
and saw it about 6% less than on vanilla python 3.2.2 (660 MB of reserved
process memory compared to 702 MB; Linux Gentoo 64bit) The application is 
written in heavy OOP style (for instance, ~1000 classes are generated by our 
ORM on the fly, and there are approximately the same amount of hand-written 
ones) so I hoped for a much bigger saving.

As for the patch itself I found one use-case, where python with the patch
behaves differently::

  class Foo:
      def __init__(self, msg):
          self.msg = msg

  f = Foo('123')

  class _str(str):
      pass

  print(f.msg)
  print(getattr(f, _str('msg')))

The above snippet works perfectly on vanilla py3.2, but fails on the patched 
one  (even on 3.3 compiled from your 'cpython_new_dict' branch)  I'm not sure
that it's a valid code, though.  If not, then we need to fix some python 
internals to add exact type  check in 'getattr', in the 'operator.getattr', etc.  
And if it is - your  patch needs to be fixed.  In any case, I propose to add 
the above code to the  python test-suite, with either expecting a result or an 
exception.

Cheers,
Yury

On 2012-02-15, at 12:58 PM, Mark Shannon wrote:

> Any opinions on my new dictionary implementation?
> 
> I'm happy to take silence on the PEP as tacit approval,
> but the code definitely needs reviewing.
> 
> Issue:
> http://bugs.python.org/issue13903
> 
> PEP:
> https://bitbucket.org/markshannon/cpython_new_dict/src/6c4d5d9dfc6d/pep-new-dict.txt
> 
> Repository
> https://bitbucket.org/markshannon/cpython_new_dict
> 
> Cheers,
> Mark.
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