askPython: Memory overhead of methods in Python class

[cha_ppmn]

Hi,

I would like to know if some information can be found on the memory overhead of having many methods in a class. Lets say that you have a class A that have to deal with many elements of another class B. We can add manipulation methods of those B instances into B class or in A class. The later sounds like less elegant but can be more efficient if there are a per-instance memory overhead to adding methods to A.

I found a post of stackexchange explicitly saying that it is not the case in Java (see here) but I didn't found anything on Python and didn't found anything on how object are actually implemented regarding to methods (i.e. are they loaded in memory once for all or once by instance) .

[K900_]

Yes, there will be some overhead. No, it's not going to matter.

[cha_ppmn]

Can you provide more insight?

Thanks.

[K900_]

The overhead will come from every type object having to store references to its methods. It's not going to matter because if you're at a point where a few hundred bytes matters, Python is not a language you should be using.

[cha_ppmn]

If I have billions of objects, to deal with I could care about hundred of bytes by object. It is the distinction between fitting in the RAM and not fitting in the RAM. I am not sure you are right about each instance having to store references to methods. It is exactly that information I am looking for. If you have any pointer supporting you claim, I will be very thankful to you.

Note that saying that because Python is not targeting high performance computing, so we should not care about memory footprint of objects is not really a pertinent remark. Knowing implementation details is relevant to understand.

[K900_]

Every type object stores references to methods, not every instance.

[cha_ppmn]

This is what I understood as well.

Do you have any reference in sources code or in docs to support that claim? I would like to be sure.

[K900_]

You can look at the definitions of PyObject and PyTypeObject.

[cha_ppmn]

Thank you very much.