[Tut] Hex String to Hex Integer in Python

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Hex String to Hex Integer in Python

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Question: Given a hexadecimal string such as

Code:

'0xf'

in Python. How to convert it to a hexadecimal number in Python so that you can perform arithmetic operations such as addition and subtraction?

The hexadecimal string representation with the

Code:

'0x'

prefix indicates that the digits of the numbers do have a hexadecimal base

Code:

16

.

In this article, I’ll show you how to do some basic conversion and arithmetic computations using the hexadecimal format. So, let’s get started!

Convert Hex to Decimal using int()

You can convert any hexadecimal string to a decimal number using the

Code:

int()

function with the

Code:

base=16

argument. For example,

Code:

'0xf'

can be converted to a decimal number using

Code:

int('0xf', base=16)

or simply

Code:

int('0xf', 16)

.

Code:

>>> int('0xf', base=16) 15 >>> int('0xf', 16) 15

Hexadecimal Number to Integer Without Quotes

Note that you can also write the hexadecimal number without the string quotes like so:

Code:

>>> 0xf 15

The

Code:

0x

prefix already indicates that it is a hexadecimal number.

Using the eval() Function



That’s why an alternative way to convert a hexadecimal string to a numerical value (integer, base 10) is to use the

Code:

eval('0xf')

function like so:

Code:

>>> eval('0xf') 15

However, I wouldn’t recommend it over the

Code:

int()

function as the

Code:

eval()

function is known to be a bit tricky and poses some security risks.

Hex Arithmetic Operators

You can simply add or subtract two hexadecimal numbers in Python by using the normal

Code:

+

and

Code:

-

operators:

Code:

>>> 0xf + 0x1 16 >>> 0xf - 0xa 5 >>> 0x1 + 0x1 2

The result is always shown in decimal values, i.e., with

Code:

base=10

.

You can display the result with

Code:

base=16

by converting it back to a hexadecimal format using the

Code:

hex()

built-in function. For example, the expression

Code:

hex(0x1 + 0x1)

yields the hexadecimal string representation

Code:

'0x2'

.



Here are a couple of examples:

Code:

>>> hex(0x1 + 0x1) '0x2' >>> hex(0xf + 0xf) '0x1e' >>> hex(0xf * 16) '0xf0'

In the last line, you multiply with the base

Code:

16

which essentially shifts the whole number one digit and inserts a digit at the right—much like multiplying with base

Code:

10

in a decimal system.

Adding Two Hex Strings



In the following example, you add together two hex strings

Code:

'0xf'

and

Code:

'0xf'

—both representing the decimal 15 so the result is decimal 30:

Code:

>>> int('0xf', 16) + int('0xf', 16) 30

If you need the result as a hex string, you can pass the whole computation into the

Code:

hex()

built-in function to obtain a hexadecimal representation of the decimal

Code:

30

:

Code:

>>> hex(int('0xf', 16) + int('0xf', 16)) '0x1e'

Subtracting and Multiplying Two Hex Strings

You can also subtract or multiply two hex strings by converting them to integers from their base

Code:

16

representations using

Code:

int(hex_str, 16)

, doing the computation in the decimal system using the normal

Code:

-

and

Code:

*

operators, and converting back to hexadecimal strings using the

Code:

hex()

function on the result.

See here:

Code:

>>> h1 = '0xf' >>> h2 = '0x1' >>> h1_int = int(h1, 16) >>> h2_int = int(h2, 16) >>> hex(h1_int - h2_int) '0xe' >>> hex(h1_int * h2_int) '0xf'

Printing Hex String without Prefix ‘0x’

To print the hexadecimal string such as

Code:

'0xffffff'

without the

Code:

'0x'

prefix, you can simply use slicing

Code:

hex_string[2:]

starting from the third character and slice all the way to the right.

A minimal example:

Code:

>>> hex_string = '0xfffffff' >>> hex_string[2:] 'fffffff'

Where to Go From Here?



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