gistfile1.py

from django import template
from django.template.defaultfilters import stringfilter
from django.utils.html import conditional_escape
from django.utils.safestring import mark_safe
import re

register = template.Library()

# (?:\A|[\s\.,:;'"])(@(\w{1,20}))(?!\.?\w)
twitterize_pattern = r'''
    (?:                 # non-capturing group
        \A              # start: match the beginning of line
        | [\s\.,:;'"]   # or any of: whitespace, period, comma, colon, etc...
    )
    (@                  # capture group \1, contains the full @username
        (\w{1,20})      # capture group \2, the 1-20 char username without @
    )
    (?!                 # but don't match if followed by
        \.?             # zero or one periods
        \w              # followed by any word character
    )'''

twitterize_replace = r'''
@<a class="tweetreply" href="http://twitter.com/\2">\2</a>'''

twitterize_regex = re.compile(twitterize_pattern, re.VERBOSE)

@register.filter()
@stringfilter
def twitterize(value, autoescape=None):
    """
    Converts all "@replies" in plain text into clickable links, while trying
    to ignore red herrings like email addresses, invalid twitter usernames.
    
    @replies can have some leading punctuation or trailing punctuation,
    but cannot
    """ 
    if autoescape:
        esc = conditional_escape
    else:
        esc = lambda x: x
    result = twitterize_regex.sub(twitterize_replace, esc(value))
    return mark_safe(result)
twitterize.is_safe = True
twitterize.needs_autoescape = True