Python: Variables & Data Types
What you will learn
How to store data in variables, the main built-in types, and how type conversion works. Python is dynamically typed — you never declare a type, and a variable can hold a string now and an integer later.
Variables
name = "Alice" # string
age = 25 # integer
height = 5.6 # float
is_student = True # boolean
Variable names: letters, digits (not first char), underscores. Case-sensitive. Convention: snake_case.
Common built-in types
| Type | Example | Mutable? | Use |
|---|---|---|---|
int |
42, -3 |
No | Whole numbers |
float |
3.14 |
No | Decimals |
str |
"hello" |
No | Text |
bool |
True, False |
No | Conditions |
list |
[1, 2, 3] |
Yes | Ordered collection |
tuple |
(1, 2, 3) |
No | Immutable sequence |
dict |
{"key": "val"} |
Yes | Key-value pairs |
set |
{1, 2, 3} |
Yes | Unique items |
Type conversion
int("25") # 25 (string to integer)
str(3.14) # "3.14" (float to string)
float("2.5") # 2.5
bool(0) # False (zero is falsy)
bool("hello") # True (non-empty is truthy)
Common mistakes
- Forgetting that dividing two ints with
/gives a float:5/2returns2.5, not2(use//for integer division). - Confusing
=(assignment) with==(equality check).
Quick check below!