Length of hexadecimal number

Question

How can we get the length of a hexadecimal number in the Python language? I tried using this code but even this is showing some error.

i = 0
def hex_len(a):
    if a > 0x0:
        # i = 0
        i = i + 1
        a = a/16
        return i
b = 0x346
print(hex_len(b))

Here I just used 346 as the hexadecimal number, but my actual numbers are very big to be counted manually.

Can you use the number of letters of the string representation? — Alex L, Jun 28 '13 at 15:14
What exactly do you mean by "Length of a hex number"? What are you expecting the length of `0x346` to be? — Justin Ethier, Jun 28 '13 at 15:15
@DavidJashi - I suppose that is obvious now, having read the question again. I must have been over-thinking it. — Justin Ethier, Jun 28 '13 at 15:27
Re *"showing some error"*: That is not such a big surprise. In the two lines with "a=a/16" and "return i" you used a mix of tabs and spaces. If you are lucky you may get away with that, but [the rules are complicated](https://stackoverflow.com/questions/2034517/pythons-interpretation-of-tabs-and-spaces-to-indent/25471702#25471702). — Peter Mortensen, Jul 03 '18 at 03:10
As it is, there is also the runtime error *UnboundLocalError: local variable 'i' referenced before assignment*. — Peter Mortensen, Jul 03 '18 at 03:21

score 7 · Accepted Answer · answered Jun 28 '13 at 15:13

7

Use the function hex:

>>> b = 0x346
>>> hex(b)
'0x346'
>>> len(hex(b))-2
3

or using string formatting:

>>> len("{:x}".format(b))
3

answered Jun 28 '13 at 15:13

Ashwini Chaudhary

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score 6 · Answer 2 · edited Jun 28 '13 at 15:30

6

While using the string representation as intermediate result has some merits in simplicity it's somewhat wasted time and memory. I'd prefer a mathematical solution (returning the pure number of digits without any 0x-prefix):

from math import ceil, log

def numberLength(n, base=16): 
    return ceil(log(n+1)/log(base))

The +1 adjustment takes care of the fact, that for an exact power of your number base you need a leading "1".

edited Jun 28 '13 at 15:30

Jon Clements

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answered Jun 28 '13 at 15:29

guidot

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"somewhat wasted time and memory"—I'm sceptical – Colonel Panic Jun 28 '13 at 15:58
Considering this is python I doubt the difference in resources matters. If it was code for an embedded controller, then maybe. But +1 for thinking beyond the "obvious" string-based solution. – Justin Ethier Jun 28 '13 at 16:05
My measurements using the timeit module gave these results: the string solution has a runtime nearly linear to the number of digits, the log solution a nearly constant one. Break even is at about 240 bit numbers. For a 32 bit number the string routine needs half the time, for a 1024 bit number the string solution needs factor 3 of the log solution. The original question mentioned **very big** numbers... – guidot Jun 29 '13 at 12:18

score 2 · Answer 3 · answered Jun 28 '13 at 15:27

2

As Ashwini wrote, the hex function does the hard work for you:

hex(x)

Convert an integer number (of any size) to a hexadecimal string. The result is a valid Python expression.

answered Jun 28 '13 at 15:27

Justin Ethier

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Length of hexadecimal number

3 Answers3