Check memory usage of your Python objects

With sys.getsizeof() you can check the memory usage of an object:

import sys

mylist = range(0, 10000)
print(sys.getsizeof(mylist))
# 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 a lot 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)]
print(sys.getsizeof(myreallist))
# 87632

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

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