[Python-Dev] Reducing memory overhead for dictionaries by removing me_hash

[Kirat Singh]

Hi, this is my first python dev post, so please forgive me if this topic has
already been discussed.

It seemed to me that removing me_hash from a dict entry would save 2/3 of
the space used by dictionaries and also improve alignment of the entries
since they'd be 8 bytes instead of 12. And sets end up having just 4 byte
entries.

I'm guessing that string dicts are the most common (hence the specialized
lookupdict_string routine), and since strings already contain their hash,
this would probably mitigate the performance impact. One could also add a
hash to Tuples since they are immutable.

If this isn't a totally stupid idea, I'd be happy to volunteer to try the
experiment and run any suggested tests.

thanks!
-Kirat

PS any opinion on making _Py_StringEq a macro? inline function would be nice
but I hesitate to bring up the C/C++ debate, both languages suck in their
own special way ;-)
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