How can I obfuscate email addresses contained in 'free input' text fields in Django

Question

In my models I often use text fields that are intended to contain large pieces of textile-formatted input. I'd like to automatically obfuscate any email addresses that are entered into these text fields, so that when they're printed in a template they're not visible to spiders.

Is there a smart way to do this?

Update:

Based on lazerscience's answer below, this was the code i ended up using. I named the file encode_mailto.py, and put it in a templatetags directory, inside a 'utilities' type app that i install into most of my django projects.

import re
import random
from django.utils.safestring import mark_safe
from django import template
register = template.Library()

email_link_pat = re.compile(r'<a\s+href=("|\')?mailto:[^>]+>[^<]*</a>')
email_pat = re.compile(r'\b[-.\w]+@[-.\w]+\.[a-z]{2,4}\b')

def get_script(m):
    code_list = []
    for c in m.group(0):
        d = ord(c)
        x = random.randint(0, d)
        code_list.append("%d+%d" % (x, d-x))

    return '<script type="text/javascript">document.write(String.fromCharCode(%s))</script>' % \
        ",".join(code_list)

def encode_mailto(text):
    text = email_link_pat.sub(get_script, text)
    text = email_pat.sub(get_script, text)
    return mark_safe(text)

register.filter('encode_mailto', encode_mailto)</pre>

Then use it in templates as follows:

{% load encode_mailto %}
{{"A bunch of text with an email address [email protected]"|encode_mailto }}

Answer 1

If you just want to use it as Template tag filter:

import re
import random
from django.utils.safestring import mark_safe


email_link_pat = re.compile(r'<a\s+href=("|\')?mailto:[^>]+>[^<]*</a>')
email_pat = re.compile(r'\b[-.\w]+@[-.\w]+\.[a-z]{2,4}\b')

def get_script(m):
    code_list = []
    for c in m.group(0):
        d = ord(c)
        x = random.randint(0, d)
        code_list.append("%d+%d" % (x, d-x))

    return '<script type="text/javascript">document.write(String.fromCharCode(%s))</script>' % \
        ",".join(code_list)

@register.filter
def encode_mailto(text):
    text = email_link_pat.sub(get_script, text)
    text = email_pat.sub(get_script, text)
    return mark_safe(text)

Then you can use it in your templates eg:

{{ "<a href='mailto:[email protected]'>Send Mail</a>"|encode_mailto }}