Generate random bytes or random Hex string in Python

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Borislav Hadzhiev

Last updated: Apr 10, 2024
6 min

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# Table of Contents

  1. Generate random bytes of length N in Python
  2. Generate random bytes of length N using random.randbytes()
  3. Generate random bytes of length N using secrets.token_bytes()
  4. Generate a random Hex string in Python
  5. Generate a random hex color in Python

# Generate random bytes of length N in Python

Use the os.urandom() method to generate random bytes of length N, e.g. random_bytes = os.urandom(8).

The os.urandom() method returns a bytestring of N random bytes suitable for cryptographic use.

main.py
import os


# ✅ create random bytestring that is 8 bytes long

random_bytes = os.urandom(8)
print(random_bytes)  # 👉️ b'\xd8\xa7\\\xe4~\xa2y\xe3'
print(len(random_bytes))  # 👉️ 8

# ------------------------------------------

# ✅ create random bytestring that is 16 bytes long

random_bytes = os.urandom(16)

# 👇️ b'\xeb\xba^\x81\xe1\x00\xb9\x0c\x99\x1e\xe9\x86\x86\x0bl]'
print(random_bytes)
print(len(random_bytes))  # 👉️ 16

generate random bytes of length n

The code for this article is available on GitHub

The os.urandom() method takes a size argument and returns a cryptographically secure bytestring of size random bytes.

How the method is implemented depends on the underlying operating system.

# Generating a random bytearray

If you need to generate a random bytearray, pass the result of calling os.urandom() to the bytearray class.

main.py
import os

random_bytearray = bytearray(os.urandom(16))
# 👇️ bytearray(b'\xe8\x87p\x11Y\xfd~\xff\xe6\xe1O\xbf\x06\xd8Om')
print(random_bytearray)

generating random bytearray

The code for this article is available on GitHub

The bytearray class copies the supplied binary data via the buffer protocol.

# Table of Contents

  1. Generate random bytes of length N using random.randbytes()
  2. Generate random bytes of length N using secrets.token_bytes()
  3. Generate a random Hex string in Python
  4. Generate a random hex color in Python

# Generate random bytes of length N using random.randbytes()

If you use a Python version newer than 3.9, you can use the newer random.randbytes() method.

The randbytes() method generates n random bytes.

main.py
import random


random_bytes = random.randbytes(8)
print(random_bytes)  # 👉️ b'\xb0\x1c\x01:L\x95 \xa3'
print(len(random_bytes))  # 👉️ 8

# ------------------------------------------

random_bytes = random.randbytes(16)

# 👇️ b'M\x9dh\xfa\xee\x93i\x02\x17\xe2\x13\xa5\x03\xebh\xc8'
print(random_bytes)
print(len(random_bytes))  # 👉️ 16

generate random bytes of length n using random randbytes

The code for this article is available on GitHub

The random.randbytes() method was introduced in Python 3.9 and generates N random bytes.

The method should not be used for generating security tokens.

# Table of Contents

  1. Generate random bytes of length N using secrets.token_bytes()
  2. Generate a random Hex string in Python
  3. Generate a random hex color in Python

# Generate random bytes of length N using secrets.token_bytes()

You can use the secrets module if you need to generate security tokens.

The token_bytes() method from the secrets module generates a cryptographically strong random byte string of N bytes.

main.py
import secrets

random_bytes = secrets.token_bytes(8)
print(random_bytes)  # 👉️ b'>C\xe3\xe3?m\xa4u'
print(len(random_bytes))  # 👉️ 8

# ------------------------------------------

random_bytes = secrets.token_bytes(16)

# 👇️ b'\x84\x84>\xe0]o\xda\x1e\xc8qL\xde\xf0\x8e\xc7\xec'
print(random_bytes)
print(len(random_bytes))  # 👉️ 16
The code for this article is available on GitHub

The secrets module is used for generating cryptographically strong random numbers for passwords, security tokens, etc.

The secrets.token_bytes method returns a random byte string of the given length.

If the number of bytes is not specified or is None, a default value is used.

main.py
import secrets


random_bytes = secrets.token_bytes()
# 👇️ b'\xcc\xed\xf2\xd6Q\x9e\x02\x02\x1d\xbe\xddu\xf9\x11\xd5\x015\xccT\xf4\xe4)/S\xd9N\xed\x0b\xb0;Xt'
print(random_bytes)

print(len(random_bytes))  # 👉️ 32

Which approach you pick is a matter of personal preference.

If you need to generate security tokens, make sure to not use the random.randbytes() method.

# Table of Contents

  1. Generate a random Hex string in Python
  2. Generate a random hex color in Python

# Generate a random Hex string in Python

To generate a random hex string:

  1. Use the os.urandom() method to get a byte string of N random bytes.
  2. Use the binascii.b2a_hex() method to return the hexadecimal representation of the binary data.
main.py
import binascii
import os

result = binascii.b2a_hex(os.urandom(10))
print(result)  # 👉️ b'a28ad94dde798a004e4d'

string = result.decode('utf-8')
print(string)  # 👉️ a28ad94dde798a004e4d

print(len(result))  # 👉️ 20

generate random hex string

The code for this article is available on GitHub

The os.urandom() method takes a size argument and returns a cryptographically secure byte string of size random bytes.

How the method is implemented depends on the underlying operating system.

The binascii.b2a_hex method returns the hexadecimal representation of the supplied binary data.

Every byte of the data is converted to the corresponding 2-digit hex representation.

# Converting the bytes object to a string

You can use the bytes.decode() method if you need to convert the bytes object to a string.

main.py
import binascii
import os

result = binascii.b2a_hex(os.urandom(10))
print(result)  # 👉️ b'a28ad94dde798a004e4d'

string = result.decode('utf-8')
print(string)  # 👉️ a28ad94dde798a004e4d

print(len(result))  # 👉️ 20

converting bytes object to string

The code for this article is available on GitHub

The bytes.decode() method returns a string decoded from the given bytes. The default encoding is utf-8.

An alternative approach is to use the random.choices() method.

# Generate a random Hex string using random.choices()

This is a two-step process:

  1. Use the random.choices() to select N digits from a sequence of hexadecimal digits.
  2. Use the str.join() method to join the N digits into a string.
main.py
import random


def gen_random_hex_string(size):
    return ''.join(random.choices('0123456789abcdef', k=size))


result = gen_random_hex_string(16)
print(result)  # 👉️ db688cb662842860
The code for this article is available on GitHub
A hexadecimal string is a sequence of hexadecimal digits (0-9, a-f, A-F), grouped in pairs.

If you also need to include the capital letters A-F, you can also use the string.hexdigits attribute.

main.py
import string


# 👇️ 0123456789abcdefABCDEF
print(string.hexdigits)

The random.choices() method returns a k sized list of elements chosen from the provided iterable with replacement.

main.py
import random

result = random.choices('0123456789abcdef', k=10)

# 👇️ ['f', '1', '0', '7', 'b', '4', 'a', '8', 'd', 'b']
print(result)
With replacement basically means that the same element can be returned multiple times.

Once we have a list of hexadecimal digits, we can use the str.join() method to join the list into a string.

main.py
import random

def gen_random_hex_string(size):
    return ''.join(random.choices('0123456789abcdef', k=size))


result = gen_random_hex_string(16)
print(result)  # 👉️ e36fd2ec559d35d1

The str.join() method takes an iterable as an argument and returns a string which is the concatenation of the strings in the iterable.

The string the method is called on is used as the separator between the elements.

# Generate a random Hex string using secrets.token_hex()

If you need to generate a cryptographically secure hex string, use the secrets module.

The token_hex() method from the secrets module returns a random text string in hexadecimal.

main.py
import secrets

result = secrets.token_hex(16)
print(result)  # 👉️ c39d47a82e4fda7cd43ca139db5cebb3

print(len(result))  # 👉️ 32

The secrets module is used for generating cryptographically strong random numbers for passwords, security tokens, etc.

The secrets.token_hex method returns a random text string in hexadecimal.

The argument the method takes is the number of random bytes the string should contain. Each byte gets converted to 2 hex digits.

# Generate a random hex color in Python

To generate a random hex color:

  1. Use the random.choices() method to select 6 random hex symbols.
  2. Use the str.join() method to join the list into a string.
  3. Use the addition (+) operator to prepend a hash symbol to the string.
main.py
import random


def gen_random_hex_color():
    hex_digits = '0123456789ABCDEF'

    return '#' + ''.join(
        random.choices(hex_digits, k=6)
    )


print(gen_random_hex_color())  # 👉️  #6DB16C
print(gen_random_hex_color())  # 👉️  #8E5D29
print(gen_random_hex_color())  # 👉️  #7593E1
The code for this article is available on GitHub

We used the random.choices() method to select 6 random hex symbols.

The hexadecimal symbols include the digits 0-9 and the characters A-F.

The random.choices method returns a k sized list of elements chosen from the provided iterable with replacement.

main.py
import random

# 👇️ ['9', 'A', 'C', 'C', '2', 'C']
print(random.choices('0123456789ABCDEF', k=6))
With replacement basically means that the same element can be returned multiple times.

# Use the random.choice() version in older Python versions

The random.choices() method was introduced in Python 3.9. If you use an older version, use the random.choice() method.

main.py
import random


def gen_random_hex_color():
    hex_digits = '0123456789ABCDEF'

    return '#' + ''.join(
        random.choice(hex_digits)
        for _ in range(6)
    )


print(gen_random_hex_color())  # 👉️  #6F1C2B
print(gen_random_hex_color())  # 👉️  #2B1364
print(gen_random_hex_color())  # 👉️  #6F8E77
The code for this article is available on GitHub

The random.choice() method takes a sequence and returns a random element from the non-empty sequence.

main.py
import random

print(random.choice('bobby')) # 👉️ "o"

Once we have a collection of random hex symbols, we can use the str.join() method to join the characters into a string.

The str.join method takes an iterable as an argument and returns a string which is the concatenation of the strings in the iterable.

The string the method is called on is used as the separator between the elements.

The last step is to use the addition (+) operator to prepend a hash symbol to the string.

main.py
import random


def gen_random_hex_color():
    hex_digits = '0123456789ABCDEF'

    return '#' + ''.join(
        random.choices(hex_digits, k=6)
    )


print(gen_random_hex_color())  # 👉️  #6DB16C

Alternatively, you can use a formatted string literal.

# Generate a random hex color using a formatted string literal

This is a two-step process:

  1. Use the random.randint() method to get 3 random numbers from 0 to 255.
  2. Use a formatted string literal to format the digits in hex.
main.py
import random


def gen_random_hex_color():
    def get_int():
        return random.randint(0, 255)

    return f'#{get_int():02X}{get_int():02X}{get_int():02X}'


print(gen_random_hex_color())  # 👉️  #A5F627
print(gen_random_hex_color())  # 👉️  #671D75
print(gen_random_hex_color())  # 👉️  #B37340
The code for this article is available on GitHub

The random.randint() function takes 2 numbers - a and b as parameters and returns a random integer in the range.

Note that the range is inclusive - meaning both a and b can be returned.

Formatted string literals (f-strings) let us include expressions inside of a string by prefixing the string with f.
main.py
var1 = 'bobby'
var2 = 'hadz'

result = f'{var1}{var2}'
print(result)  # 👉️ bobbyhadz

Make sure to wrap expressions in curly braces - {expression}.

Formatted string literals also enable us to use the format specification mini-language in expression blocks.

The :02 syntax is used to pad each value with leading zeros to a fixed width of 2.

main.py
def gen_random_hex_color():
    def get_int():
        return random.randint(0, 255)

    return f'#{get_int():02X}{get_int():02X}{get_int():02X}'


print(gen_random_hex_color())  # 👉️  #A5F627
print(gen_random_hex_color())  # 👉️  #671D75
The code for this article is available on GitHub

If the generated number is less than 10, it gets padded to 2 digits.

The X character stands for hex format.

It outputs the number in base 16, using uppercase letters for the digits above 9.

The last step is to add a hash symbol at the beginning of the string.

Which approach you pick is a matter of personal preference. I'd use the random.choices() method because I find it easier to read.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

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