Python · Lesson 2 of 9

Variables & data types

Creating variables, int, float, str, bool and converting between types.

A variable is a name that points to a value. You create one by assigning with = — no keyword needed. Names use snake_case by convention.

int — whole numbers: 25
float — decimals: 4.5
str — text: "Kochi" or 'Kochi'
bool — True or False (capital letters)
None — “no value yet”

type(x) tells you a value's type. Convert with int(), float(), str() — for example int("42") gives the number 42.

Try it yourself

Code editor

Press Run to see the output.

Edit and press Run (or Ctrl/⌘ + Enter). Python runs in your browser — the first run downloads the Python engine and takes a few seconds.

Key points

Assign with = ; no declaration keyword.
True / False / None are capitalised.
Convert text to numbers with int() or float() before calculations.

Quick check

What does int("7") + 3 give?

"73" 10 An error 7.3

Practice task

Create variables for a job title, a monthly salary and the number of openings. Print the yearly salary (monthly × 12).

Interview corner

What is dynamic typing?

In Python a variable has no fixed type — the value does. The same name can point to an int now and a str later. Type errors appear at run time rather than at compile time.

What is the difference between a mutable and an immutable type?

Mutable objects (list, dict, set) can be changed in place. Immutable objects (int, float, str, tuple) cannot — 'changing' them creates a new object.