Is there any way to find out sizeof an object

["Martin v. Löwis"]

> I have written a class which has some attributes. I want to know how
> do i find out the size of an instance of this class??
> class T(object):
>     def __init__(self, fn_name, *args, **kwds):
>         self.fn_name = fn_name
>         self.args = args
>         self.kwds = kwds

In Python 2.6, you can use sys.getsizeof to find out how large an object
is. Notice that this is a really tricky question: Assuming you have

   t = T(1,2,3, a="hello", b="world")

then you should certainly consider the size atleast

   sys.getsizeof(t) + sys.getsizeof(t.__dict__)

But then you also have the attribute values (i.e. the tuple resp.
dict), which you might want to account for:

   + sys.getsizeof(t.args) + sys.getsizeof(t.dict)

Now, what to do about the sizes of the various items in the dict
and the tuple? One could do

  total = ... # from above
  for o in t.args:
      total+=sys.getsizeof(o)
  for k,v in t.kwds.items():
      total+=sys.getsizeof(k)+sys.getsizeof(v)

However, that might be accounting too much, since the at least
the keys of the dict are shared across other dicts. Likewise,
the integers are shared, and the string literals (as written
above) would be shared if the very same T constructor is run
twice.

In short, "size of an instance" can't be answered without
a specific instance (i.e. you can't answer it in advance for
all instances), plus even for a single instance, its difficult
to answer.

Regards,
Martin