fixed numbering, fixed file() typo, take rules file as an argument in plural5.py

examples/plural5.py

@@ -14,14 +14,14 @@ def build_match_and_apply_functions(pattern, search, replace):
         return re.sub(search, replace, word)
     return [matches_rule, apply_rule]
 
-def rules():
-    with open('plural5-rules.txt') as pattern_file:
+def rules(rules_filename):
+    with open(rules_filename) as pattern_file:
         for line in pattern_file:
             pattern, search, replace = line.split(None, 3)
             yield build_match_and_apply_functions(pattern, search, replace)
 
-def plural(noun):
-    for matches_rule, apply_rule in rules():
+def plural(noun, rules_filename='plural5-rules.txt'):
+    for matches_rule, apply_rule in rules(rules_filename):
         if matches_rule(noun):
             return apply_rule(noun)
     raise ValueError('no matching rule for {0}'.format(noun))