from re import *

def pluralize(noun, funcs):
     for matches_rule, apply_rule in funcs:
         if matches_rule(noun):
             return apply_rule(noun)
     raise ValueError("no matching rule for {0}".format(noun))


def build_match_and_apply_functions(pattern, search, replace):
     def matches_rule(word):
         return re.search(pattern, word)
     def apply_rule(word):
         return re.sub(search, replace, word)
     return (matches_rule, apply_rule)


class LazyRules:
     rules_filename = 'rules.txt' #a class variable - shared across all instances of the LazyRules class
     def __init__(self):
         self.pattern_file = open(self.rules_filename, encoding="utf-8")
         self.cache=[]
     def __iter__(self):
         self.cache_index=0
         return self #returning self signals that this class defines a __next__ method
     def __next__(self):
         self.cache_index += 1
         if len(self.cache) >= self.cache_index:
             return self.cache[self.cache_index-1]
         if self.pattern_file.closed:
             raise StopIteration
         line = self.pattern_file.readline()
         if not line: #if there's a line to read, it will not be an empty string (even if new row, it will be "n")
             self.pattern_file.close()
             raise StopIteration
         pattern,search,replace= line.split(None,3)
         funcs = build_match_and_apply_functions(pattern,search,replace)
         self.cache.append(funcs) # before returning the match&apply functions, we save them in the list self.cache
         return funcs

[sxz]$               $    es
[^aeioudgkprt]h$     $    es
[^aeiou]y$          y$    ies
$                    $    s

import pluralizer
funcs = pluralizer.LazyRules()
p = pluralizer.pluralize("baby", funcs)

NameError: name 're' is not defined