Check memory usage of your Python objects

With sys.getsizeof() you can check the memory usage of an object. To do so, first import the module sys:

import sys

mylist = range(0, 10000)
# 48

Woah… wait… why is this huge list only 48 bytes?

It’s because the range function returns an iterable object that only behaves like a list of numbers, but internally simply keeps count of the last iteration number. A range is magnitudes more memory efficient than using an actual list of numbers.

You can see for yourself by using a list comprehension to create an actual Python list of numbers from the same range:

import sys

myreallist = [x for x in range(0, 10000)]
# 87632

That’s roughly 87KB for 10,000 numbers.

Not very accurate

One thing to note: this method is not very accurate. sys.getsizeof will not recursively calculate the memory usage of all objects in a list or dictionary. So when requesting the size of a list, you request only the size of the list itself and all its references to the content, but the size of all those integers themselves is not taken into account. E.g., a Python integer takes up 28 bytes by itself:

>>> import sys
>>> sys.getsizeof(1)
>>> 10000 * 28

10K integers will take up an additional 280K or so bytes of memory, in addition to the list size of 87K.

Get certified with our courses

Learn Python properly through small, easy-to-digest lessons, progress tracking, quizzes to test your knowledge, and practice sessions. Each course will earn you a downloadable course certificate.

Leave a Comment

Python Newsletter

Before you leave, you may want to sign up for my newsletter.

Tips & Tricks
Course discounts

Googler exit intent popup

No spam & you can unsubscribe at any time.

Share to...