6 
import sys


class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y


v1 = Vector(1, 2)
v2 = Vector(1, 2)
print(f"v1 __dict__ : {sys.getsizeof(v1.__dict__)} bytes")
print(f"v2 __dict__ : {sys.getsizeof(v2.__dict__)} bytes")

v3 = Vector(1, 2)
v4 = Vector(1, 2)
print(f"v3 __dict__ : {sys.getsizeof(v3.__dict__)} bytes")
print(f"v4 __dict__ : {sys.getsizeof(v4.__dict__)} bytes")

v5 = Vector(1, 2)
print(f"v5 __dict__ : {sys.getsizeof(v5.__dict__)} bytes")

v6 = Vector(1, 2)
print(f"v6 __dict__ : {sys.getsizeof(v6.__dict__)} bytes")

Anyone can tell me why the result of the code above is

v1 __dict__ : 288 bytes
v2 __dict__ : 288 bytes
v3 __dict__ : 272 bytes
v4 __dict__ : 272 bytes
v5 __dict__ : 264 bytes
v6 __dict__ : 256 bytes

I try to ask AI and the explanation seems to be strange and i can't understand that clearly.

and if I move the print statement up and down ,it will lead to different results,so why this matters?

Why v2 and v3 differ?

I found the code acts differently from various python versions,and the result above is in Python3.13

A really strange phenomenon for me ,thank you all .

Improve this question
10
  • This question is similar to: Why is the __dict__ of instances so much smaller in size in Python 3?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. Commented Jun 27 at 11:54
  • 2
    @user2722968 This question isn't about the difference between python versions, it's about the difference between instances in the same version. Commented Jun 27 at 13:55
  • 1
    See also: sys.getsizeof is not what you want that alludes to internal book keeping and overallocation of memory Commented Jun 27 at 14:57
  • 2
    @Barmar the answer that explains the split table implementation for key-sharing attribute dicts may actually be the answer here, though I think this could serve as an independent question and shouldn't be closed as a duplicate. Commented Jun 27 at 15:26
  • 1
    Running it longer shows me that the size shrinks by 8 bytes for each new instance until it reaches 88 bytes. Commented Jun 27 at 17:18
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