Python Memory Model

Why variables are name bindings not boxes, how PyObject refcounting works, the small int cache that makes is lie, and how closures keep state alive after their creator returns.

Stage 1 — Names, Not Boxes1 / 22

Namespace dict

empty

C / C++ model

int x = 5;

x IS a memory slot. Assignment copies the value.

Python model

x = 5

x is a name in a dict. Assignment binds the name.

points to

Heap (PyObjects)

empty

FastSlow

In C, a variable IS a memory box — int x = 5 writes the value 5 directly into a stack slot. In Python, a variable is a NAME — a label in a dictionary that points to an object living on the heap. This single distinction explains most Python "surprises".

Key facts

x = 5binds name, doesn't copy

y = xtwo names, one object

x = 10rebinds x, y unchanged

b = adangerous for mutables!

a[:]shallow copy of a list

Progress

Names, Not Boxes

PyObject & Refcount

Small Int Cache

Frames & Closures

Active Recall Quiz

Q1 of 3

a = [1,2,3]; b = a; b.append(4). What does print(a) output?

Under the Hood

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DNSresolving host

TCPconnecting

TLShandshake

HTTPrequesting

DSAverse

Python Memory Model

Python Memory Model