# using module re to pluralize most common english words
# (rule_tuple used as function default, so establish it first)
 
import re
 
# (pattern, search, replace) regex english plural rules tuple
rule_tuple = (
('[ml]ouse$', '([ml])ouse$', '\\1ice'), 
('child$', 'child$', 'children'), 
('booth$', 'booth$', 'booths'), 
('foot$', 'foot$', 'feet'), 
('ooth$', 'ooth$', 'eeth'), 
('l[eo]af$', 'l([eo])af$', 'l\\1aves'), 
('sis$', 'sis$', 'ses'), 
('man$', 'man$', 'men'), 
('ife$', 'ife$', 'ives'), 
('eau$', 'eau$', 'eaux'), 
('lf$', 'lf$', 'lves'), 
('[sxz]$', '$', 'es'), 
('[^aeioudgkprt]h$', '$', 'es'), 
('(qu|[^aeiou])y$', 'y$', 'ies'), 
('$', '$', 's')
)
 
def regex_rules(rules=rule_tuple):
    for line in rules:
        pattern, search, replace = line
        yield lambda word: re.search(pattern, word) and re.sub(search, replace, word)
 
def plural(noun):
    for rule in regex_rules():
        result = rule(noun)
        if result: 
            return result
 
# testing ...
print plural("man")    # men
print plural("woman")  # women
print plural("lady")   # ladies
print plural("wife")   # wives
print plural("leaf")   # leaves
# okay according to Webster ...
print plural("index")  # indexes
print plural("fungus") # funguses    
# etc.