Convert Hex String to Int in Python

1. Use int() to Convert Hex to Int in Python
2. Convert Non-Prefixed Hex String to Int in Python
3. Convert Prefixed Hex String to Int in Python
4. Convert Little and Big Endian Hex String to Int in Python
5. Convert Hex to Signed Integer in Python

This tutorial will demonstrate how to convert the hex string to int in Python. It will cover different hex formats like signed, little, and big-endian, 0x annotated hexadecimal, and the default hex string.

Use int() to Convert Hex to Int in Python

The most common and effective way to convert hex into an integer in Python is to use the type-casting function int().

This function accepts two arguments: one mandatory argument, which is the value to be converted, and a second optional argument, which is the base of the number format with the default as 10.

Other number formats are 2 for binary, 8 for octal, and 16 for hexadecimal. If you put 0 as the argument for the base value, it will derive the number format from the value’s prefix. If there isn’t any prefix, it will automatically recognize it as a decimal, 0b for binary, 0o for octal, and 0x for hexadecimal.

Convert Non-Prefixed Hex String to Int in Python

If the hexadecimal string is not prefixed, then specify the base value of the int() function to be 16.

For example:

hex_val = 'beef101'

print(int(hex_val, 16))

Output:

200208641

The result is the decimal or integer conversion of the hex value beef101.

Convert Prefixed Hex String to Int in Python

If the hex string has a prefix 0x, then change the base value argument to 0 to detect the prefix automatically.

You can still pass 16 as the base, but if you’re dealing with multiple values with different number formats, passing 0 is the best approach.

hex_val = '0xdeadcab'

print(int(hex_val, 0))
print(int(hex_val, 16))

Output:

233495723
233495723

Convert Little and Big Endian Hex String to Int in Python

Little endian and big-endia byte orders are two types of ordering systems for hexadecimal. The default order is little-endian, which puts the most significant number in the right-most part of the sequence, while the big-endian does the opposite.

With that in mind, all we have to consider is to convert the big-endian hexadecimal value into a little-endian. Afterward, the usual conversion can now be performed on it.

To convert a big-endian hexadecimal string to a little-endian one, use bytearray.fromhex() and use the function reverse() on the result. Afterward, convert the hexadecimal value back to string and convert it to an integer.

big_endian = 'efbe'

def to_little(val):
  little_hex = bytearray.fromhex(val)
  little_hex.reverse()
  print("Byte array format:", little_hex)

  str_little = ''.join(format(x, '02x') for x in little_hex)

  return str_little

little_endian = to_little(big_endian)

print("Little endian hex:", little_endian)
print("Hex to int:", int(little_endian, 16))

To summarize this code block:

• Call bytearray.fromhex() to convert the big-endian hex string into a byte array hexadecimal value.
• Reverse the byte array to convert the big-endian into a little-endian format.
• Convert the byte array value back into a string hex format in little-endian.
• Convert the string into an integer using int().

Output:

Byte array format: bytearray(b'\xbe\xef')
Little endian hex: beef
Hex to int: 48879

Convert Hex to Signed Integer in Python

Converting any number format into a signed integer would need an operation called the Two’s Complement, which is a bitwise mathematical operation to compute for signed numbers.

So before we can convert hexadecimal into a signed integer, we would need to define a function that will carry out the Two’s Complement operation.

def twosComplement_hex(hexval):
    bits = 16 # Number of bits in a hexadecimal number format
    val = int(hexval, bits)
    if val & (1 << (bits-1)):
    val -= 1 << bits
    return val

The left-most bit in a binary value is called the signed bit, determining if the integer is positive or negative. This function will reserve that bit as the signed bit and shift the other bits to compensate by using the bitwise left shift operator <<.

Now, moving on to the actual conversion of the hex value to signed int.

hex_val1 = 'ff'
hex_val2 = 'ffff'
hex_val3 = 'aaff'

def twosComplement_hex(hexval):
    bits = 16
    val = int(hexval, bits)
    if val & (1 << (bits-1)):
        val -= 1 << bits
    return val
  
print(twosComplement_hex(hex_val1))
print(twosComplement_hex(hex_val2))
print(twosComplement_hex(hex_val3))

Output:

255
-1
-21761

Now, we’ve achieved converting a hex string into a signed integer.

In summary, we have covered converting different types of hexadecimal formats into signed and unsigned integers. Use int() with the value and base arguments to convert a hex into an unsigned integer.

If the hexadecimal is in a big-endian format, convert it into a little-endian format first using bytearray.fromhex() and reverse().

Lastly, if you need to convert a hex string to a signed integer, then perform the Two’s Complement operation on the hexadecimal value on it to get a signed integer value.