An integer is a whole-number value. In Python, its type is called int: 0, 5, and -4 are integers. A value’s type determines which operations you can use with it. For example, you can add two integers with 1 + 2 to get 3. section 5.2
An integer is not the same type as a float, even when their values look similar: 1 is an int, while 1.0 is a float. You can check a value’s type with type(), such as type(3). section 5.2 section 5.3
The int() constructor also converts suitable values to integers:
- int("4") gives 4. The first value is a string; the result is an integer. int("a") causes an error because the string is not a number. section 5.3
- int(3.94) gives 3: conversion removes the decimal part. int(False) gives 0, and int(True) gives 1. section 5.3
Table 5.1. Mathematical operations on ints and floats and the resulting types
| Operation(s) |
Type of second object |
Type of result |
Example |
||
|---|---|---|---|---|---|
| int | + - * ** % | int | int | 3 + 2 3 - 2 3 * 2 3 ** 2 3 % 2 | gives 5 gives 1 gives 6 gives 9 gives 1 |
| int | / | int | float | 3 / 2 | gives 1.5 |
| int | + - * / ** % | float | float | 3 + 2.0 3 - 2.0 3 * 2.0 3 / 2.0 3 ** 2.0 3 % 2.0 | gives 5.0 gives 1.0 gives 6.0 gives 1.5 gives 9.0 gives 1.0 |
| float | + - * / ** % | int | float | 3.0 + 2 3.0 - 2 3.0 * 2 3.0 / 2 3.0 ** 2 3.0 % 2 | gives 5.0 gives 1.0 gives 6.0 gives 1.5 gives 9.0 gives 1.0 |
| float | + - * / ** % | float | float | 3.0 + 2.0 3.0 - 2.0 3.0 * 2.0 3.0 / 2.0 3.0 ** 2.0 3.0 % 2.0 | gives 5.0 gives 1.0 gives 6.0 gives 1.5 gives 9.0 gives 1.0 |
Compare the result types as well as the numbers: 3 + 2 produces an int, but 3 / 2 produces the float 1.5. Operations mixing an int and a float also produce floats in the examples shown. section 5.3
Find whole hours
Suppose you need to express 123 minutes as hours and leftover minutes. Dividing by 60 gives 2.05; int(123 / 60) gives 2 whole hours. The leftover minutes need a separate calculation. Try the same first step with 800 minutes: what whole-hour count do you get? section 6.3
Listing 11.5. Calculations with user input
user_input = input("Enter a number to find the square of: ") #1
num = int(user_input) #2
print(num*num) #3
input() supplies a string, even when someone types a number. This program converts that string with int() before multiplying the number by itself. section 11.2
Integers are useful beyond ordinary arithmetic. In a string expression, an integer can specify how many repetitions to make: "-" * 10 creates ten dashes. section 8.2
