CODEWITHSUNDEEP
pythonmemorysizeofcomplex-numbers
audeoudh
audeoudh

Reputation: 1479

What's the relationship between size of integer and complex objects?

I recently heard about Python integer cache. After having searched on internet, I have found this well-written article : http://www.laurentluce.com/posts/python-integer-objects-implementation. It explains what I wanted to know about this subject.

In this article, it explains why a integer object is not only 16 or 32 bits wide, as in C. Indeed, Python needs to store the object header (because a int Python integer is an object) and the value of this integer (with long C type, so at least 32 bits according to http://en.wikipedia.org/wiki/C_data_types).

On my machine, I get :

>>> x = 5
>>> type(x)
<type 'int'>
>>> sys.getsizeof(x)
12

Ok. So a Python int object is 12 bytes wide.

My question comes from a comparison between integer and complex sizes. I typed, on the same machine :

>>> z = 5 + 5j
>>> type(z)
<type 'complex'>
>>> sys.getsizeof(z);
24

I believe that complex is an object. So, as int, each complex object has to store its object header. But, if the header of a int plus its value equals 12, why does the header of complex (same size as int, I suppose !) plus its value (2 times the size of an integer ?) equals 24 ?

Many thanks in advance !

Upvotes: 1

Views: 1241

Answers (2)

Kasravnd
Kasravnd

Reputation: 107307

Its because of that complex numbers are represented as a pair of floating point number:

An imaginary literal yields a complex number with a real part of 0.0. Complex numbers are represented as a pair of floating point numbers and have the same restrictions on their range. To create a complex number with a nonzero real part, add a floating point number to it, e.g., (3+4j). Some examples of imaginary literals:

Upvotes: 1

jonrsharpe
jonrsharpe

Reputation: 122067

Because a complex contains two floats, not two integers: 

>>> import sys
>>> z = 5 + 5j
>>> z.imag
5.0
>>> z.real
5.0
>>> sys.getsizeof(z.imag)
16
>>> sys.getsizeof(z.real)
16
>>> sys.getsizeof(z)
24

You can see the complexobject source code in the Python repo.

Upvotes: 1

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