Memory-usage of dictionary in Python?

Question

I am slightly confused when I use the getsizeof method in the sys module for dictionaries. Below I have created a simple dictionary of two strings.

Answer 1

From the PythonDocs

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

So it only counts the overhead, but you can use the function in this link to calculate it for containers like dicts.

Answer 2

Well, dictionaries don't store the actual string inside them, it works a bit like C/C++ pointers, so you only get a constant overhead in the dictionary for every element.

The total size is

size = getsizeof(d)
size += sum(map(getsizeof, d.itervalues())) + sum(map(getsizeof, d.iterkeys()))

Answer 3

The recursive getsizeof would get the actual size, but if you have multiple layers of dictionaries and only want to get a rough estimate. The json comes handy.

>>> first = 'abc'*1000
>>> second = 'def'*1000
>>> my_dictionary = {'first': first, 'second': second}
>>> getsizeof(first)
3049
>>> getsizeof(second)
3049
>>> getsizeof(my_dictionary)
288
>>> getsizeof(json.dumps(my_dictionary))
6076
>>> size = getsizeof(my_dictionary)
>>> size += sum(map(getsizeof, my_dictionary.values())) + sum(map(getsizeof, my_dictionary.keys()))
>>> size
6495