Stage 1 · 20 min · 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 and bool apart
• Use type() to see a type
• Name variables correctly

Why learn this

Programs need to remember information: a user's name, a score, a price. A variable is a "labelled box" to store that information and get it back.

Concept

Write variable_name = value to create a variable. In Python, = means assignment (putting a value in the box), not "is equal to".

The four basic types: int is a whole number (10, -3), float is a decimal number (3.14, 5.0), str is text ("Lan"), bool is true/false (True, False).

Variable names contain letters, digits and _, can't start with a digit and have no spaces. Prefer meaningful names like math_score 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 explanation

1. Line 1: creates the variable ten holding the string "Lan".
2. Line 2: creates the variable tuoi holding the integer 15.
3. Line 3: takes the old value 15, adds 1 and assigns it back to tuoi, so tuoi is now 16.
4. Line 4: prints the values, separated by spaces.
5. Line 5: type(ten) tells you that ten is a str.

Common mistakes

2ten = "Lan"

ten2 = "Lan"

ho ten = "Lan"

ho_ten = "Lan"

print(Tuoi)

print(tuoi)

Summary

• = is assignment.
• int, float, str and bool are the 4 basic types.
• type() tells you a value's type.
• Variable names are case-sensitive; choose meaningful names.