How do I convert a hex string to an int in Python?

I may have it as "0xffff" or just "ffff".

12 Answers

Without the 0x prefix, you need to specify the base explicitly, otherwise there's no way to tell:

x = int("deadbeef", 16) 

With the 0x prefix, Python can distinguish hex and decimal automatically.

>>> print(int("0xdeadbeef", 0)) 3735928559 >>> print(int("10", 0)) 10 

(You must specify 0 as the base in order to invoke this prefix-guessing behavior; if you omit the second parameter int() will assume base-10.)

int(hexstring, 16) does the trick, and works with and without the 0x prefix:

>>> int("a", 16) 10 >>> int("0xa", 16) 10 

Convert hex string to int in Python

I may have it as "0xffff" or just "ffff".

To convert a string to an int, pass the string to int along with the base you are converting from.

Both strings will suffice for conversion in this way:

>>> string_1 = "0xffff" >>> string_2 = "ffff" >>> int(string_1, 16) 65535 >>> int(string_2, 16) 65535 

Letting int infer

If you pass 0 as the base, int will infer the base from the prefix in the string.

>>> int(string_1, 0) 65535 

Without the hexadecimal prefix, 0x, int does not have enough information with which to guess:

>>> int(string_2, 0) Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: invalid literal for int() with base 0: 'ffff' 

literals:

If you're typing into source code or an interpreter, Python will make the conversion for you:

>>> integer = 0xffff >>> integer 65535 

This won't work with ffff because Python will think you're trying to write a legitimate Python name instead:

>>> integer = ffff Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'ffff' is not defined 

Python numbers start with a numeric character, while Python names cannot start with a numeric character.

For any given string s:

int(s, 16) 

Adding to Dan's answer above: if you supply the int() function with a hex string, you will have to specify the base as 16 or it will not think you gave it a valid value. Specifying base 16 is unnecessary for hex numbers not contained in strings.

print int(0xdeadbeef) # valid myHex = "0xdeadbeef" print int(myHex) # invalid, raises ValueError print int(myHex , 16) # valid 

The worst way:

>>> def hex_to_int(x): return eval("0x" + x) >>> hex_to_int("c0ffee") 12648430 

Please don't do this!

Is using eval in Python a bad practice?

Or ast.literal_eval (this is safe, unlike eval):

ast.literal_eval("0xffff") 

Demo:

>>> import ast >>> ast.literal_eval("0xffff") 65535 >>> 

If you are using the python interpreter, you can just type 0x(your hex value) and the interpreter will convert it automatically for you.

>>> 0xffff 65535 

The formatter option '%x' % seems to work in assignment statements as well for me. (Assuming Python 3.0 and later)

Example

a = int('0x100', 16) print(a) #256 print('%x' % a) #100 b = a print(b) #256 c = '%x' % a print(c) #100 

Handles hex, octal, binary, int, and float

Using the standard prefixes (i.e. 0x, 0b, 0, and 0o) this function will convert any suitable string to a number. I answered this here: but here is the needed function.

def to_number(n): ''' Convert any number representation to a number This covers: float, decimal, hex, and octal numbers. ''' try: return int(str(n), 0) except: try: # python 3 doesn't accept "010" as a valid octal. You must use the # '0o' prefix return int('0o' + n, 0) except: return float(n) 

In Python 2.7, int('deadbeef',10) doesn't seem to work.

The following works for me:

>>a = int('deadbeef',16) >>float(a) 3735928559.0 

with '0x' prefix, you might also use eval function

For example

>>a='0xff' >>eval(a) 255