How do I determine the size of an object in Python?

Just use the sys.getsizeof function defined in the sys module.

sys.getsizeof(object[, default]):

Return the size of an object in bytes.
The object can be any type of object.
All built-in objects will return
correct results, but this does not
have to hold true for third-party
extensions as it is implementation
specific.

Only the memory consumption directly attributed to the object is
accounted for, not the memory consumption of objects it refers to.

The default argument allows to define
a value which will be returned if the
object type does not provide means to
retrieve the size and would cause a
TypeError.

getsizeof calls the object’s
__sizeof__ method and adds an additional garbage collector overhead
if the object is managed by the
garbage collector.

See recursive sizeof recipe for an example of using getsizeof() recursively to find the size of containers and all their contents.

Usage example, in python 3.0:

>>> import sys
>>> x = 2
>>> sys.getsizeof(x)
24
>>> sys.getsizeof(sys.getsizeof)
32
>>> sys.getsizeof('this')
38
>>> sys.getsizeof('this also')
48

If you are in python < 2.6 and don’t have sys.getsizeof you can use this extensive module instead. Never used it though.