Python Numbers

Numbers are one of the most common things you’ll use in programming. Just like in everyday life, we need numbers to count, measure, and calculate. In Python, numbers are treated as special data types, which means the computer knows how to work with them in a mathematical way.

For example, you might want to:

Keep track of a score in a game.
Work out the total price of shopping.
Measure a distance or a temperature.
Calculate someone’s age from their birth year.

Python makes all of this possible by giving us different types of numbers, each designed for a specific job. The two you’ll start with are:

Integer (int) – whole numbers (…−3, −2, −1, 0, 1, 2, 3…).
Examples: 0, 7, -42, 2025
Floating-point (float) – numbers with a decimal point.
Examples: 3.14, -0.5, 2.0, 1e3 (which means 1000.0)

a = 7          # int
b = 3.5        # float
c = 1e3        # float (scientific notation = 1000.0)

print(type(a)) # <class 'int'>
print(type(b)) # <class 'float'>

Try it

Make one int and one float. Print both and use type() to check their types.

Basic arithmetic

Python supports the usual arithmetic operators:

Operator	Meaning	Example	Result
`+`	addition	`7 + 3`	`10`
`-`	subtraction	`7 - 3`	`4`
`*`	multiplication	`7 * 3`	`21`
`/`	true division	`7 / 2`	`3.5` (float)
`//`	floor division	`7 // 2`	`3` (int)
`%`	remainder (modulo)	`7 % 2`	`1`
`**`	power	`2 ** 3`	`8`

print(7 / 2)   # 3.5
print(7 // 2)  # 3
print(7 % 2)   # 1
print(2 ** 5)  # 32

Order of operations (BODMAS/PEMDAS) applies: brackets first, then powers, then multiply/divide, then add/subtract.

print(2 + 3 * 4)     # 14
print((2 + 3) * 4)   # 20

Try it

Work out 9 // 4, 9 % 4, and 9 / 4.
Predict 3 + 2 ** 3 * 2, then run it to check.

Mixing ints and floats

If an operation mixes int and float, the result is a float:

print(3 + 2.0)   # 5.0
print(7 / 2)     # 3.5 (division is always float)

Converting types

int(x) converts to an integer (truncates towards zero).
float(x) converts to a float.
str(x) converts to text (string).

age = "18"
print(int(age) + 1)   # 19

height = 172
print(float(height))  # 172.0

Try it

Convert "3.9" to a float and add 1.
Convert 5.9 to an int: what do you get, and why?

Input from a user (and converting it)

input() always returns a string, so you must convert it before doing maths.

year = int(input("Birth year: "))
age = 2025 - year
print(f"You are about {age} years old.")

Try it

Ask for two numbers with input(), convert them to float, and print their average.

Rounding and absolute values

print(round(3.14159, 2))  # 3.14  (2 decimal places)
print(round(2.5))         # 2 or 3? (Banker’s rounding: to nearest even)
print(abs(-7))            # 7 (distance from zero)

Note: Python’s round() uses “banker’s rounding”: round(2.5) → 2, round(3.5) → 4.

Try it

Round 9.995 to 2 decimal places.
Use abs() to turn -123 into positive.

Floating-point gotchas (precision)

Floats are stored in binary, which can’t represent some decimals exactly. You may see tiny errors:

print(0.1 + 0.2)      # 0.30000000000000004
print(round(0.1 + 0.2, 2))  # 0.3 (display nicely)

This is normal in many languages. If exact decimal money maths matters, use decimal.Decimal:

from decimal import Decimal, getcontext
getcontext().prec = 28

price = Decimal("0.10") + Decimal("0.20")
print(price)  # 0.30

Try it

Print 0.3 == 0.1 + 0.2. Then print Decimal("0.3") == Decimal("0.1") + Decimal("0.2").

Comparisons and tests

Use comparison operators to ask true/false questions:

Operator	Meaning	Example	Result
`==`	equal to	`5 == 5`	True
`!=`	not equal to	`5 != 3`	True
`<`	less than	`2 < 7`	True
`<=`	less or equal	`7 <= 7`	True
`>`	greater than	`10 > 3`	True
`>=`	greater or equal	`3 >= 4`	False

Try it

Write a program that asks for a test score (0–100) and prints Pass if it’s >= 50, else Fail.

A few handy maths tools

The built-in math module gives extra functions:

import math

print(math.sqrt(16))   # 4.0
print(math.pi)         # 3.141592653589793
print(math.ceil(3.2))  # 4  (round up)
print(math.floor(3.8)) # 3  (round down)

Try it

Compute the area of a circle with radius r = 2.5 using math.pi * r ** 2.

Mini practice set (answers by running the code)

Write a calculator that reads two numbers and prints: sum, difference, product, true division, floor division, remainder.
Given seconds = 3672, print hours, minutes, seconds (e.g., 1h 1m 12s) using // and %.
Ask for someone’s height in centimetres and print metres as a float with two decimal places.
Create x = 0.1; add it to itself 10 times. Why isn’t it exactly 1.0? Show a round(..., 10) version.
Use Decimal to add 0.1 three times and show that it equals 0.3 exactly.

Common beginner mistakes (and fixes)

Forgetting to convert input n = input("Number: ") print(n + 1) # ❌ TypeError (string + int) print(int(n) + 1) # ✅
Surprised by division print(7 / 2) # 3.5 (float) print(7 // 2) # 3 (floor division)
Float comparison print(0.1 + 0.2 == 0.3) # False (precision) print(round(0.1 + 0.2, 10) == 0.3) # True-ish for display

Summary

Integers are whole numbers; floats include decimals.
Use standard operators (+ - * / // % **) and remember order of operations.
Convert types with int(), float(), str(), and convert input() before maths.
Floats can show tiny precision errors; for exact decimal work, use decimal.Decimal.
round(), abs(), and math functions are your friends.