CODEWITHSUNDEEP
python
Akavall
Akavall

Reputation: 86266

Why is single int 24 bytes, but in list it tends to 8 bytes

Here is what I am looking at:

In [1]: import sys

In [2]: sys.getsizeof(45)
Out[2]: 24

In [3]: sys.getsizeof([])
Out[3]: 72

In [4]: sys.getsizeof(range(1000))
Out[4]: 8072

I know that int in Python is growable (can get bigger that 24 bytes) objects that live on the heap, and I see why that object can be quite large, but isn't a list just a collections of such objects? Apparently it is not, what is going on here?

Upvotes: 6

Views: 502

Answers (3)

dan04
dan04

Reputation: 91179

A list is a collection of pointers to objects, not of the objects themselves. So, assuming a 64-bit system, your list has 8000 bytes of pointers plus 72 bytes of overhead.

Upvotes: 2

kindall
kindall

Reputation: 184270

The list doesn't contain any integers; it contains pointers to various objects, which happen to be integers and which are stored elsewhere. getsizeof() tells you the size only of the object you pass to it, not of any additional objects it points to.

Upvotes: 8

Simeon Visser
Simeon Visser

Reputation: 122456

This is the size of the object - excluding the objects it contains:

>>> d = range(10)
>>> sys.getsizeof(d)
152
>>> d[0] = 'text'
>>> sys.getsizeof(d)
152
>>> d
['text', 1, 2, 3, 4, 5, 6, 7, 8, 9]

The size of the list with 1000 elements, in your case, is 8072 bytes but each integer object is still 24 bytes. The list object keeps track of these integer objects but they're not included in the size of the list object.

Upvotes: 9

Related Questions