Python Variables

Satellite · Data Types

Python Variables

Variables are labels pointing to objects. Understand assignment semantics so you never accidentally overwrite shared data.

Practice assignmentsReview mutability

Assignment

count = 10
name = "Ada"

• Variables don't have types; the objects they reference do.
• Multiple assignment works: x = y = [] (be careful with mutables).

Unpacking

lat, lon = location
a, *rest = [1, 2, 3, 4]

Naming conventions

• snake_case for variables/functions
• UPPER_SNAKE_CASE for constants (MAX_RETRIES)
• Avoid single-letter names except for temporary loops

Scope

Scope	Description
Local	Inside current function
Enclosing	Parent function scopes
Global	Module-level
Builtins	Provided by Python

Use global and nonlocal sparingly; prefer passing values explicitly.

Mutability reminders

config = {"debug": True}
alias = config
alias["debug"] = False
# config now shows debug False, too

Copy mutable objects when you need isolation: copy = config.copy().

Next up in your learning path

Type casting

Convert between strings, ints, floats, and more.

Companion

Constants best practices

Keep configuration organized and immutable.

Deep dive

Work with lists next

See how variables reference mutable collections.

Next satellite

Frequently Asked Questions

Is there block scope in Python?

No. Variables defined inside loops or if statements leak into the surrounding scope. Only functions define new scopes.

How do I declare constants?

Python has no true constant keyword. Use naming conventions (UPPER_SNAKE_CASE) and keep them at module level. Tools like mypy can flag reassignment if you annotate with `Final`.

Why does `x is y` sometimes return True for small integers?

CPython caches small integers and strings, so identities may match. Always use `==` for value comparison.