On Tue, Jul 23, 2013 at 9:09 AM, Jim Mooney <cybervigila...@gmail.com>wrote:
> I've noticed that when I create a number of objects from a class, one > after another, they're at different IDs, but the IDs all appear to be > equidistant, so that they all appear to have the same size. But what does > that size represent? is it bytes? ie - if I run this over and over I get > different id numbers but they are always 40 apart. Or is that distance > machine-specific as to units?: > > In Python, the id is just a number that identifies the object. You can't count on it to represent object size, or anything else for that matter. The only requirement for python implementations is that different objects can not have the same id. The CPython implementation uses the memory address of the object as its id because it's simple and satisfies the above requirement. Still, i'd say it's very unsafe to try to infer object sizes from this. It depends on how memory addresses work on your machine, what type of memory allocator is used and how much overhead it has, and many more factors. Furthermore, other python implementations (I believe Jython and IronPython among them) do not even use memory addresses as id numbers, but simply assign consecutive integers to each created object. In general, relying on the id number to tell you anything other than whether two variables point to the same object is highly unreliable at best and impossible in the general case. HTH, Hugo
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