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Convert hex string to int in Python


Question

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

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

2016/05/14
1
789
5/14/2016 2:52:52 AM

Accepted Answer

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; omitting the second parameter means to assume base-10.)

2017/04/12
1126
4/12/2017 12:21:19 AM

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

>>> int("a", 16)
10
>>> int("0xa",16)
10
2013/01/08

For any given string s:

int(s, 16)
2008/10/16

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.

2020/06/20

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
2012/06/30

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?

2017/05/23

Source: https://stackoverflow.com/questions/209513
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