'''Pluralize English nouns (stage 5)

Command line usage:
$ python plural5.py noun
nouns
'''

import re

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]

def rules(rules_filename):
    with open(rules_filename, encoding='utf-8') 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, 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))

if __name__ == '__main__':
    import sys
    if sys.argv[1:]:
        print(plural(sys.argv[1]))
    else:
        print(__doc__)

# Copyright (c) 2009, Mark Pilgrim, All rights reserved.
# 
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# are permitted provided that the following conditions are met:
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#   this list of conditions and the following disclaimer.
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