Python data types: int, float, str, bool, list, tuple, dict and set

Every value in Python has a type: a whole number, a piece of text, a list of things… The type decides what you can do with the value. 10 + 5 is 15, but "10" + "5" is "105". In this first lesson you'll meet the eight types you'll use every day: int, float, str, bool, list, tuple, dict and set. You'll see what each one is for, and how to check a value's type yourself. Every example runs right here: press Run, then Edit to change it.

Variables and print(), in one minute

Two things you need first. A variable is a name for a value, made with =. print() shows a value. Everything after # is a comment, a note Python skips:

a = 10        # a is now 10
print(a)      # shows 10

And type() tells you a value's type:

a = 10
print(type(a))

<class 'int'> means: this is an int. Now let's meet them all.

Numbers: int and float

An int (integer) is a whole number, with no decimal point. A float is a number with a decimal point:

a = 10       # int
b = 10.5     # float

print(a, type(a))
print(b, type(b))
print(a + b)        # 20.5: an int plus a float gives a float
print(7 / 2)        # 3.5: dividing always gives a float
print(7 // 2)       # 3: two slashes divide and drop the decimals

Use an int for things you count (people, clicks, lives in a game), and a float for things you measure (prices, heights, temperatures).

Text: str

A str (string) is text. You write it in quotes, "double" or 'single', as long as both ends match:

c = "Hello"
name = 'Ada'

print(c, name)
print(type(c))
print(len(c))          # 5: how many characters
print(c.upper())       # HELLO
print(c + " " + name)  # joining strings with +

The quotes are what make it a string. 10 is a number, but "10" is text that happens to contain digits:

print(10 + 10)      # 20
print("10" + "10")  # 1010: two strings joined

Yes or no: bool

A bool (boolean) is either True or False. In Python they start with a capital letter:

h = True
is_raining = False

print(h, type(h))
print(5 > 3)    # True: a comparison gives a bool
print(5 == 3)   # False: == asks "is it equal?"

true (lower case) is an error in Python: it looks for a variable called true. You'll use bools all the time in the lesson on if.

Many values in order: list

A list keeps several values in order, inside square brackets. You can change it: add, remove and replace items.

d = [1, 2, 3, 4, 5]
fruits = ["apple", "banana", "cherry"]

print(fruits[0])     # apple: counting starts at 0
print(fruits[-1])    # cherry: -1 is the last one
print(len(fruits))   # 3

fruits.append("mango")   # add to the end
fruits[1] = "kiwi"       # replace the second item
print(fruits)

The position of an item is its index, and the first index is 0, not 1. A list can hold any type, even mixed: [1, "two", 3.0, True].

A list that never changes: tuple

A tuple is like a list, but in round brackets, and it can't be changed after you make it. That's called immutable:

f = (1, 2, 3, 4, 5)
point = (3, 7)

print(f[0])         # 1: reading works like a list
print(point)

point[0] = 10       # changing it doesn't

The last line stops with a TypeError. That's the point of a tuple: use it for values that belong together and shouldn't change, like the x and y of a point, or a date (2026, 11, 11).

Names and values: dict

A dict (dictionary) stores key-value pairs, in curly brackets. Instead of asking "what's at position 0?", you ask "what's the value for name?":

e = {"name": "John", "age": 30}

print(e["name"])     # John
print(e["age"])      # 30

e["age"] = 31            # change a value
e["city"] = "Lund"       # add a new pair
print(e)
print(e.keys())

Each key appears only once. Use a dict when your data has labels: a user (name, email, age), a product (title, price), the settings of an app.

Unique values: set

A set holds values without duplicates and without order, also in curly brackets, but with no key: parts:

g = {"a", "b", "c", "d", "e"}
numbers = {1, 2, 2, 3, 3, 3}

print(numbers)          # {1, 2, 3}: duplicates are dropped
print("a" in g)         # True: is it in the set?
print(len(g))           # 5

Because a set has no order, it has no index: g[0] is an error, and printing it may show the items in a different order each time. Use a set to remove duplicates, or to check quickly whether something is in a group:

visitors = ["ana", "bo", "ana", "cy", "bo"]
unique = set(visitors)
print(unique)
print(len(unique), "different visitors")

All eight at a glance

Here are your eight from the start of the lesson, with their types:

a = 10
b = 10.5
c = "Hello"
d = [1, 2, 3, 4, 5]
e = {"name": "John", "age": 30}
f = (1, 2, 3, 4, 5)
g = {"a", "b", "c", "d", "e"}
h = True

for value in [a, b, c, d, e, f, g, h]:
    print(type(value).__name__, "→", value)

(The for line goes through the values one by one. You'll learn it properly in the lesson on loops.)

Changing a type

You can turn a value into another type with the type's name:

print(int("42") + 1)       # 43: text to a whole number
print(float("2.5") * 2)    # 5.0: text to a decimal
print(str(100) + "%")      # 100%: number to text
print(list("abc"))         # ['a', 'b', 'c']
print(set([1, 1, 2]))      # {1, 2}

You'll need int() a lot: when a user types a number, Python gives it to you as text.

Common mistakes

Exercise

name = "Lina"
age = 19
height = 1.72
is_member = True
grades = [8, 9, 7]
student = {"name": name, "age": age}

print(type(name), type(age), type(height), type(is_member))
print(type(grades), type(student))
print("Second grade:", grades[1])

Quick check

s = {1, 2, 2, 3}
print(len(s))