Stage 1 · 20 minutes · Free

Variables and data types

What a variable is, how to name variables, the four basic data types int, float, str, bool, and the type() function.

Objectives

• Create variables and assign values
• Tell int, float, str, bool apart
• Use type() to see a type
• Name variables by the rules

Why learn this

A program needs to remember information: a user name, a score, a price. A variable is a 'labelled box' for storing and retrieving that information.

Concept

Write ten_bien = gia_tri to create a variable. The = in Python means assignment (storing a value in the box), not 'equals'.

Four basic types: int is an integer (10, -3), float is a real number (3.14, 5.0), str is a text string ("Lan"), bool is true/false (True, False).

A variable name contains letters, digits and _, does not start with a digit, and has no spaces. Use meaningful names like diem_toan instead of x.

Assigning a new value replaces the old one.

Syntax

ten = "Lan"
tuoi = 15
chieu_cao = 1.55
da_dang_ky = True
print(type(tuoi))

Example

ten = "Lan"
tuoi = 15
tuoi = tuoi + 1
print(ten, "năm sau", tuoi, "tuổi")
print(type(ten))

Output:

Lan năm sau 16 tuổi
<class 'str'>

Line-by-line walkthrough

1. Line 1: create the variable ten holding the string "Lan".
2. Line 2: create the variable tuoi holding the integer 15.
3. Line 3: take the old value 15, add 1, and assign it back into tuoi; now tuoi is 16.
4. Line 4: print the values, separated by spaces.
5. Line 5: type(ten) tells you ten has type str.

Common mistakes

2ten = "Lan"

ten2 = "Lan"

ho ten = "Lan"

ho_ten = "Lan"

print(Tuoi)

print(tuoi)

Summary

• = is assignment.
• int, float, str, bool are the 4 basic types.
• type() tells you the type of a value.
• Variable names are case-sensitive, so pick meaningful names.