Variables in Python

Names bind to objects at assignment time. Python is dynamically typed; names don’t carry types—objects do.

Assignment and multiple assignment

Parallel assignment and unpacking keep code concise; swaps need no temp variable.

x = 1
x, y = 10, 20
x, y = y, x
first, *rest = [1,2,3,4]
head, *_, tail = [1,2,3,4]  # ignore middle

Mutability and identity

Assignment binds names; lists and dicts are mutable, tuples and strings are immutable.

a = [1, 2]
b = a           # b references the same list
b.append(3)
# a is now [1, 2, 3]

Copy when you need independence:

import copy
b = a.copy()          # shallow copy
c = copy.deepcopy(a)  # deep copy

Scope (LEGB)

Resolution order: Local, Enclosing, Global, Built‑in.

g = 0

def outer():
    x = 1
    def inner():
        nonlocal x
        x += 1
    inner()
    return x

• Use global sparingly to assign to module‑level names
• Use nonlocal to write to an enclosing function’s variable

Naming

• snake_case for variables/functions, CapWords for classes
• UPPER_CASE for constants by convention
• Avoid shadowing built‑ins like list, dict, str

Annotations (optional)

Type hints document intent and enable tooling.

count: int = 0
from typing import List
names: List[str] = ["Ada", "Guido"]

Summary

• Assignment binds names; unpacking/swap are idiomatic
• Understand mutability and LEGB to avoid surprises
• Use annotations for clarity and better tooling