Python int function – Ultimate Guide

In this tutorial I will share how the int() function works in python, the purpose of the function, different parameter types the function accepts

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In this tutorial I will share how the int() function works in python, the purpose of the function, different parameter types the function accepts. I will also share example which make the function fails and some use cases where this function is really useful.

The int() function will return an integer constructed from a number or a string. If you pass no arguments, the function will return 0

This function accepts two argument, first the number to convert and second the base of the previous number. If no base is passed, the default base is 10. 

number = int(number_text)


<class 'int'>

If you like to use a custom base, the first parameter should be a string, bytes or byte array type. See the example below:

number_base16 = int('17',16)

number_base3 = int('3',4)



Otherwise, if you passed a float as first parameter and try to convert it to an integer with an specific base for instance base 16, you will get the following error:

number_base16 = int(17.5,16)


Traceback (most recent call last):
  File line 1, in <module>
    number_base16 = int(17.5,16)
TypeError: int() can't convert non-string with explicit base

Example #1: Convert string to int

number_text="1234" # number saved in text
number = int(number_text)


<class 'int'>

Example #2: Convert float to int

float_var = 4.3
int_num = int(float_var)



Keep in mind the int function doesn’t do any rounding, it will just remove the decimal part.

Python int variable size

Since Python 3 there is no limit to the value of integers( Check out the Documentation) . However there is the constant sys.maxsize, value 9223372036854775807 (9,223,372,036,854,775,807) which can be used as an integer, larger than any practical list or string index. That means that sys.maxsize is the maximum a collection index can handle, therefore the maximum number of items the collection can hold.a list See the example below:

import sys



Python int function exercises and solutions

So far we have seen how to use int function and the different parameters the function accepts. Next I will share some exercises where the int function is necessary.

Example #1

First exercise is reading a number entered by the user, and return the absolute number. See the code below:

num = input('Enter a number:')
abs_value = abs(int(num))
print('Absolute Value: '+ str(abs_value))


In line 1 will read the number entered by the user. This number is a string. Next line will convert the string to an absolute value. Since the abs() function only accepts numbers, I need to use the int() function and convert the num variable to number.

Example #2

Another exercise exercise is reading two numbers from the user and return the result of adding the two numbers. The code below illustrates how to achieve that:

num1 = input('Enter a number:')
num1 = int(num1)
num2 = input('Enter a number:')
num2 = int(num2)
print('Result: ' + str(num1 + num2))

In this example above the int() function is used to convert a string to an integer in line 2 and line 4. The num1 and num2 variables need to be converted to integers before the addition can be calculated.

Python int function rounding

The int function will round the number to the whole part toward zero. It will leave the whole part and truncate the decimal part

float1_var = 4.6



Frequent errors

ValueError: invalid literal for int() with base 10

What if you pass to the function something that is not convertible to a number, for instance a character. The function will return the ValueError: invalid literal for int() with base 10, which indicates the parameter passed to the function is not a base 10 number. See an example below:

number1 = int('q')


Traceback (most recent call last):
  File line 1, in <module>
    number1 = int('q')
ValueError: invalid literal for int() with base 10: 'q'


To summarise, this article covers how to use the int() function, a few examples of how to use it and frequent errors to avoid. I hope this tutorial was useful and thank you for reading and supporting the this blog. 

Happy Coding!!

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