[Python-Dev] PEP 42: sizeof(obj) builtin

[M.-A. Lemburg]

Tim Peters wrote:
> [Raymond Hettinger]
> 
>>I'm about to start working on this one and wanted
>>to check here first to make sure there is still a
>>demand for it and to get ideas on the best implementation
>>strategy.
> 
> 
> Marc-Andre implemented it for mxTools:
> 
>     http://www.lemburg.com/files/python/mxTools.html
> 
>     sizeof(object)
> 
>     Returns the number of bytes allocated for the given Python object.
>     Additional space allocated by the object and stored in pointers is not
>     taken into account (though the pointer itself is). If the object
>     defines tp_itemsize in its type object then it is assumed to be a
>     variable size object and the size is adjusted accordingly.
> 
> I don't know whether anyone finds it useful in real life; maybe MAL has an
> idea about that.

Some do; I wrote this for cache management to at least
have a hint at the memory size being used by the objects in
the cache.

>>I'm thinking of summing all of the tp_basicsize slots
>>while recursing through tp_traverse.
> 
> So you'd add in the size of 0.0 a million times when traversing
> 
>     [0.0] * 1000000
> 
> ?  That wouldn't be useful.  Keeping a memo to avoid double-counting might
> be useful, but then it also gets more complicated, and so much better to
> write it in Python building on something straighforward like mxTool's
> version.

That's what I always telling people too ;-) sizeof() in
mxTools is only way to get at the tp_basicsize value, nothing
more. The rest can easily be done in Python itself.

-- 
Marc-Andre Lemburg
CEO eGenix.com Software GmbH
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