50 lines
1.6 KiB
Python
50 lines
1.6 KiB
Python
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import unittest
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import nltk
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from nltk.grammar import CFG
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class ChomskyNormalFormForCFGTest(unittest.TestCase):
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def test_simple(self):
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grammar = CFG.fromstring(
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"""
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S -> NP VP
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PP -> P NP
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NP -> Det N | NP PP P
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VP -> V NP | VP PP
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VP -> Det
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Det -> 'a' | 'the'
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N -> 'dog' | 'cat'
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V -> 'chased' | 'sat'
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P -> 'on' | 'in'
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"""
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)
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self.assertFalse(grammar.is_flexible_chomsky_normal_form())
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self.assertFalse(grammar.is_chomsky_normal_form())
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grammar = grammar.chomsky_normal_form(flexible=True)
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self.assertTrue(grammar.is_flexible_chomsky_normal_form())
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self.assertFalse(grammar.is_chomsky_normal_form())
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grammar2 = CFG.fromstring(
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"""
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S -> NP VP
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NP -> VP N P
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VP -> P
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N -> 'dog' | 'cat'
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P -> 'on' | 'in'
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"""
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)
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self.assertFalse(grammar2.is_flexible_chomsky_normal_form())
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self.assertFalse(grammar2.is_chomsky_normal_form())
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grammar2 = grammar2.chomsky_normal_form()
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self.assertTrue(grammar2.is_flexible_chomsky_normal_form())
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self.assertTrue(grammar2.is_chomsky_normal_form())
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def test_complex(self):
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grammar = nltk.data.load("grammars/large_grammars/atis.cfg")
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self.assertFalse(grammar.is_flexible_chomsky_normal_form())
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self.assertFalse(grammar.is_chomsky_normal_form())
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grammar = grammar.chomsky_normal_form(flexible=True)
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self.assertTrue(grammar.is_flexible_chomsky_normal_form())
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self.assertFalse(grammar.is_chomsky_normal_form())
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