6.1 Introduction to Variables

flowchart TD V["Variable"] V --> R["References\nlabel, not a box"] V --> M["Stack vs Heap\nwhere things live"] V --> C["Copying\nshallow vs deep"] V --> G["Garbage Collection\nrefcounting + cycles"] V --> S["Scope\nLEGB"] V --> F["Function Arguments\nmutable vs immutable"]

The topics this chapter covers, once the basic syntax of declaring and naming variables is already familiar.

What Is a Variable, Really?

What Is It?

Syntactically, a variable is just a name bound with = — that part is covered in 4.8 Variables. Underneath that syntax, a variable is a name bound to an object living in memory, not a container holding a value directly.

Why Does It Matter?

Whether a variable “contains” a value or merely points at one changes how assignment, function calls, and copying behave — this is the single idea the rest of this chapter builds on.

>>> server_name = "web01"
>>> print(server_name)
web01

How Is It Used?

Assign with =, then refer to the name anywhere afterward in the same scope — the mechanics of where it’s visible are covered in 6.8 Variable Scope.

Already Covered Elsewhere

This chapter assumes the basics are familiar and doesn’t re-teach them. If any of the following are new, read these first:

Declaring, assigning, and dynamically typing variables — 4.8 Variables
Naming rules and PEP 8 conventions — 4.7 Identifiers
The UPPER_SNAKE_CASE constant convention — 4.9 Constants
Every value being an object with identity/type/value — 5.2 Python Object Model

Real-World Examples

current_user = "alice" — tracking who’s logged in
retry_count = 0 — tracking state across a loop
response = requests.get(url) — holding a result for later use

Variables in DevOps Scripts

DevOps scripts lean on variables constantly to avoid hardcoding values that change per environment (expanded on in 6.11 Variables in DevOps):

region = "us-east-1"
instance_type = "t3.medium"
max_retries = 3

print(f"Launching {instance_type} in {region}")

Quick Interview Answer

“Syntactically a variable is a name bound with =, but underneath, it’s a label pointing at an object living in memory — not a box holding a value. That distinction is why assignment copies a reference rather than data, why mutable and immutable arguments behave differently in functions, and why copying a list needs copy/deepcopy instead of plain assignment.”

Common Mistakes

Treating a variable as a box that “holds” a value, then being surprised that b = a shares one object instead of duplicating it (see 6.2 Objects and Variable References).
Assuming this chapter re-explains naming rules or basic assignment — that groundwork lives in Chapter 4: Python Syntax.