# Convert hex string to integer in Python

## Question:

How do I convert a hex string to an integer?

``````"0xffff"   ⟶   65535
"ffff"     ⟶   65535
``````

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

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

For any given string s:

``````int(s, 16)
``````

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.)

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

print int(myHex) # invalid, raises ValueError
print int(myHex , 16) # valid
``````

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
``````

## Please don’t do this!

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

>>> hex_to_int("c0ffee")
12648430
``````

Why is using 'eval' a bad practice?

15000+ examples of this in the wild.

# 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.

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
``````

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: https://stackoverflow.com/a/58997070/2464381 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)
``````
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