How to Convert Hex to Byte in Python

1. Initialize a Hexadecimal Value
2. Use the bytes.fromhex() Function to Convert Hex to Byte in Python
3. Use the binascii Module to Convert a Hex to Byte in Python
4. Use the codecs.decode() Method to Convert a Hex to Byte in Python
5. Use List Comprehension and the int() Function to Convert a Hex to Byte in Python
6. Conclusion

Hexadecimal, often abbreviated as hex, uses 16 symbols (0-9, a-f) to represent values, contrasting with decimal’s 10 symbols. For instance, 1000 in decimal is 3E8 in hex.

Proficiency in handling hex is crucial for programming tasks involving binary data, memory addresses, and low-level encoding. This tutorial will introduce how to convert hexadecimal values into a byte literal in Python.

Initialize a Hexadecimal Value

Let’s create a hexadecimal value using a string and convert the phrase A quick brown fox into a hex value using the hexlify() function in the binascii module.

To convert a string into hexadecimal, we first need to convert the string into bytes.

import binascii

str_val = "A quick brown fox".encode("utf-8")
hex_val = binascii.hexlify(str_val).decode("utf-8")

print(hex_val)

Output:

4120717569636b2062726f776e20666f78

Now, we’ve successfully converted a string into hexadecimal. Next, let’s proceed to convert hexadecimal back into bytes.

Use the bytes.fromhex() Function to Convert Hex to Byte in Python

The bytes.fromhex() method is designed to convert a valid hexadecimal string into a bytes object. It has the following syntax:

bytes.fromhex(hex_string)

• hex_string: This is a required argument and represents the input hexadecimal string that you want to convert into a byte literal.

Here’s how the bytes.fromhex() method works:

1. Input Validation: The method first validates the input hex_string to ensure that it contains only valid hexadecimal characters (digits 0-9 and lowercase or uppercase letters A-F). If the string contains any other characters, it will raise a ValueError.
2. Parsing Pairs: The method processes the hexadecimal string two characters at a time, treating each pair of characters as a single hexadecimal byte. This means that for every two characters in the input string, one byte is generated in the resulting bytes object.
3. Conversion to Bytes: Each pair of hexadecimal characters is converted into its binary equivalent.
4. Constructing the bytes Object: As the method processes the pairs of hexadecimal characters, it constructs a bytes object by appending the binary representation of each byte. This process continues until the entire input string has been processed.
5. Return Value: Once the entire input string has been processed, the method returns the resulting bytes object, which represents the byte literal equivalent of the input hexadecimal string.

As an example, we will take the hex value from the previous result and use fromhex() to convert it into a byte literal.

hex_val = "4120717569636b2062726f776e20666f78"

print(bytes.fromhex(hex_val))

Output:

b'A quick brown fox'

Let’s break down the example hexadecimal string 4120717569636b2062726f776e20666f78 to better understand how it’s converted into a byte literal:

• 41 becomes the byte 65 (ASCII value of 'A').
• 20 becomes the byte 32 (ASCII value of space).
• 71 becomes the byte 113 (ASCII value of 'q').
• 75 becomes the byte 117 (ASCII value of 'u').
• 69 becomes the byte 105 (ASCII value of 'i').
• 63 becomes the byte 99 (ASCII value of 'c').
• 6b becomes the byte 107 (ASCII value of 'k').
• 20 becomes the byte 32 (ASCII value of space).
• 62 becomes the byte 98 (ASCII value of 'b').
• 72 becomes the byte 114 (ASCII value of 'r').
• 6f becomes the byte 111 (ASCII value of 'o').
• 77 becomes the byte 119 (ASCII value of 'w').
• 6e becomes the byte 110 (ASCII value of 'n').
• 20 becomes the byte 32 (ASCII value of space).
• 66 becomes the byte 102 (ASCII value of 'f').
• 6f becomes the byte 111 (ASCII value of 'o').
• 78 becomes the byte 120 (ASCII value of 'x').

When all these bytes are combined, you get the byte literal A quick brown fox, which is the final result.

Use the binascii Module to Convert a Hex to Byte in Python

The binascii Python module contains efficient utility functions for binary and ASCII operations. Particularly, unhexlify() is a function within the binascii module that converts a hexadecimal value into a byte literal.

This function has the following syntax:

binascii.unhexlify(hex_string)

• hex_string: This is the required argument representing the input hexadecimal string that you want to convert into a byte literal.

Here’s a detailed explanation of how it works:

1. Input Validation: The method starts by validating the hex_string argument to ensure it contains only valid hexadecimal characters. Any invalid characters in the input string will result in a binascii.Error exception.
2. Hexadecimal Pair Conversion: Next, the method processes the hex_string in pairs of characters. For example, 41 represents the byte with the integer value 65 (ASCII value of A).
3. Conversion to Bytes: The hexadecimal byte pairs are converted into their binary representation. Each pair is transformed into a corresponding byte, with each character representing 4 bits.
4. Constructing the Byte Literal: As the method processes each pair, it appends the resulting binary bytes to form a complete byte literal. This process continues until the entire input string has been processed.
5. Return Value: Once the entire hex_string has been processed, the unhexlify() function returns the resulting byte literal, represented as a bytes object.

Let’s initialize a new example with special non-ASCII characters, which will then be converted into a hexadecimal value. The example will be the Greek translation of the phrase A quick brown fox.

import binascii
from binascii import unhexlify

str_val = "Μια γρήγορη καφέ αλεπού".encode(
    "utf-8"
)  # A quick brown fox in Greek translation
hex_val = binascii.hexlify(str_val).decode("utf-8")

print("String value: ", str_val.decode("utf-8"))
print("Hexadecimal: ", hex_val)
print("Byte value: ", unhexlify(hex_val))

Output:

String value:  Μια γρήγορη καφέ αλεπού
Hexadecimal:  ce9cceb9ceb120ceb3cf81ceaeceb3cebfcf81ceb720cebaceb1cf86cead20ceb1cebbceb5cf80cebfcf8d
Byte value:  b'\xce\x9c\xce\xb9\xce\xb1 \xce\xb3\xcf\x81\xce\xae\xce\xb3\xce\xbf\xcf\x81\xce\xb7 \xce\xba\xce\xb1\xcf\x86\xce\xad \xce\xb1\xce\xbb\xce\xb5\xcf\x80\xce\xbf\xcf\x8d'

We have now successfully converted hexadecimal values to bytes.

Use the codecs.decode() Method to Convert a Hex to Byte in Python

The codecs.decode() function can also be used to convert a hexadecimal string into bytes. It’s part of Python’s codecs module, which provides various encoding and decoding functionalities for different data representations.

It has the following syntax:

codecs.decode(data, encoding, errors="strict")

• data: This is the required argument representing the data that you want to decode. In this case, it should be the hexadecimal string you wish to convert into a byte literal.
• encoding: This is also a required argument specifying the encoding to use for decoding. When working with hexadecimal strings, you should use the hex encoding to indicate that the input string represents a hexadecimal value.
• errors (optional): This argument specifies how to handle decoding errors, such as when the input string contains invalid characters for the specified encoding. It has a default value of strict, but you can change it to ignore or replace to handle errors differently.

Here’s a detailed explanation of how this method works when used for decoding hexadecimal values:

1. Input Validation: The method first checks the validity of the data argument to ensure it contains only valid hexadecimal characters. If the input string contains any non-hexadecimal characters, it will raise a UnicodeDecodeError with details about the problematic character.
2. Decoding Process: The codecs.decode() function interprets the data argument as a hexadecimal string and converts it into binary data. It processes the input string in pairs of characters, treating each pair as a single hexadecimal byte.
3. Encoding Specification: The encoding argument is crucial in this context. When you specify 'hex' as the encoding, it tells Python to interpret the input string as a hexadecimal value and convert it accordingly.
4. Conversion to Bytes: As the method processes each pair of hexadecimal characters, it converts them into their binary representation. This transformation results in the creation of a byte literal, where each pair of characters corresponds to a single byte.
5. Return Value: The codecs.decode() method returns the resulting byte literal as a bytes object, representing the decoded binary data.

See the example below:

import codecs

hex_val = "4120717569636b2062726f776e20666f78"
byte_val = codecs.decode(hex_val, "hex")
print(byte_val)

This program decodes the hex_val string using the codecs.decode() function with the encoding argument set to 'hex'. This means it will interpret the input string as a hexadecimal value and convert it to bytes.

Output:

b'A quick brown fox'

Use List Comprehension and the int() Function to Convert a Hex to Byte in Python

This method involves using list comprehension and the int() function to convert a hexadecimal string into bytes.

hex_val = "4120717569636b2062726f776e20666f78"
byte_val = bytes([int(hex_val[i : i + 2], 16) for i in range(0, len(hex_val), 2)])
print(byte_val)

Here, the code uses a list comprehension to iterate over the hexadecimal string in pairs of two characters, converts each pair to an integer in base 16 (hexadecimal), and creates a list of these integers.

The bytes() constructor is then used to convert this list of integers into a bytes object.

Output:

b'A quick brown fox'

This method is especially useful when we have a hexadecimal string with a known structure and we want to convert it into bytes efficiently. It provides control over the conversion process by allowing us to specify the encoding base (in this case, base 16 for hexadecimal).

Conclusion

In this article, we’ve covered a few ways to convert hexadecimal values to byte literals in Python.

The fromhex() function is preferable if you don’t want added imports into your source code. Otherwise, you can choose the method that best suits your needs and coding style.