Python Numbers and Casting

Python has three number types, and it is easy to convert values from one type to another.

The Three Number Types

students = 35
temperature = 31.6
z = 2 + 3j
print(type(students))
print(type(temperature))
print(type(z))

<class 'int'>
<class 'float'>
<class 'complex'>

Basic Maths

a = 17
b = 5
print(a + b)
print(a - b)
print(a * b)
print(a / b)
print(a // b)
print(a % b)
print(a ** 2)

22
12
85
3.4
3
2
289

Notice that / always gives a float, even when the answer is whole. // divides and drops the decimal part. % gives the remainder.

Useful Number Functions

print(round(3.14159, 2))
print(round(7.6))
print(abs(-250))
print(max(12, 45, 8))
print(min(12, 45, 8))
print(pow(2, 5))

3.14
8
250
45
8
32

Casting: Changing the Type

Casting means converting a value to another type.

print(int(9.8))
print(int("120"))
print(float(4))
print(float("2.75"))
print(str(50) + " rupees")

9
120
4.0
2.75
50 rupees

int() does not round. It simply removes the part after the decimal point.

Why Casting Matters: input()

The input() function reads what the user types, but it always returns a string. To do maths with it, convert it first:

qty = input("How many kg of apples? ")   # user types 3
price_per_kg = 280
total = int(qty) * price_per_kg
print(f"Total: Rs {total}")

How many kg of apples? 3
Total: Rs 840

Without int(), Python would raise an error, because you cannot multiply text by a number in this way.

Random Numbers

Python has a built-in module called random:

import random
print(random.randint(1, 6))   # like rolling a dice

The result changes every time you run it, a whole number from 1 to 6.

Exercise