Django singularize filter

To make a new custom filter I created a templatetags/ directory in my app directory. After that I added an empty __init__.py file and a template file with the following content:

from django import template
register = template.Library()

import re

SINGULARS= [
 (r's$', ''),
 (r'(n)ews$', '\1ews'),
 (r'([ti])a$', '\1um'),
 (r'((a)naly|(b)a|(d)iagno|(p)arenthe|(p)rogno|(s)ynop|(t)he)ses$', '\1\2sis'),
 (r'(^analy)ses$', '\1sis'),
 (r'([^f])ves$', '\1fe'),
 (r'(hive)s$', '\1'),
 (r'(tive)s$', '\1'),
 (r'([lr])ves$', '\1f'),
 (r'([^aeiouy]|qu)ies$', '\1y'),
 (r'(s)eries$', '\1eries'),
 (r'(m)ovies$', '\1ovie'),
 (r'(x|ch|ss|sh)es$', '\1'),
 (r'([m|l])ice$', '\1ouse'),
 (r'(bus)es$', '\1'),
 (r'(o)es$', '\1'),
 (r'(shoe)s$', '\1'),
 (r'(cris|ax|test)es$', '\1is'),
 (r'(octop|vir)i$', '\1us'),
 (r'(alias|status)es$', '\1'),
 (r'^(ox)en', '\1'),
 (r'(vert|ind)ices$', '\1ex'),
 (r'(matr)ices$', '\1ix'),
 (r'(quiz)zes$', '\1'),
 ]

@register.filter
def singularize(word):
 for pattern,replacement in SINGULARS:
   word, n =  re.subn(pattern, replacement, word)
   if n>0:
     break
 return word

The regular expressions I took from Ruby on Rails.