[Python-Dev] PEP for new dictionary implementation (original) (raw)

Mark Shannon mark at hotpy.org
Sat Feb 11 22:22:01 CET 2012

Antoine Pitrou wrote:

Hello Mark,

I think the PEP should explain what happens when a keys table needs resizing when setting an object's attribute.

If the object is the only instance of a class, it remains split, otherwise the table is combined. Most OO code will set attributes in the init method so all attributes are set before a second instance is created. For more complex use patterns, it is impossible to know what is the best approach, so the implementation allows extra insertions up to the point of a resize when it reverts to the combined table (non-shared keys). (This may not be the case in the bitbucket repository, I'll push the newer version tomorrow).

Reading the implementation, it seems the sharing can disappear definitely, which seems a bit worrying.

It is immediately re-split (to allow sharing) when only one instance of the class exists. I've implemented it that way (resize->combined then re-split) as most resizes (999 out of 1000) will be of combined tables, and I don't want to complicate the fast path.

Cheers, Mark.

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