Writing a string.ishex function

[chandra]

Folks,

I am new to Python and could not find a function along the lines of
string.ishex in Python. There is however, a string.hexdigits constant
in the string module. I thought I would enhance the existing modlue
but am unsure how I should go about it. Specifically, I have attempted
this much:
---cut---
#! /usr/bin/python
# -*- coding: utf-8 -*-

import string

def ishex(string):
    ishex = False
    for i in string:
        if i in string.hexdigits:
            ishex = True
        else:
            ishex = False
            break
    return ishex
---cut---

Can someone help me get further along please?

Thanks.