Initial commit

venv/lib/python3.7/site-packages/nltk/test/unit/test_cfg2chomsky.py

@@ -0,0 +1,49 @@
+# -*- coding: utf-8 -*-
+import unittest
+import nltk
+from nltk.grammar import CFG
+
+
+class ChomskyNormalFormForCFGTest(unittest.TestCase):
+    def test_simple(self):
+        grammar = CFG.fromstring(
+            """
+          S -> NP VP
+          PP -> P NP
+          NP -> Det N | NP PP P
+          VP -> V NP | VP PP
+          VP -> Det
+          Det -> 'a' | 'the'
+          N -> 'dog' | 'cat'
+          V -> 'chased' | 'sat'
+          P -> 'on' | 'in'
+        """
+        )
+        self.assertFalse(grammar.is_flexible_chomsky_normal_form())
+        self.assertFalse(grammar.is_chomsky_normal_form())
+        grammar = grammar.chomsky_normal_form(flexible=True)
+        self.assertTrue(grammar.is_flexible_chomsky_normal_form())
+        self.assertFalse(grammar.is_chomsky_normal_form())
+
+        grammar2 = CFG.fromstring(
+            """
+          S -> NP VP
+          NP -> VP N P
+          VP -> P
+          N -> 'dog' | 'cat'
+          P -> 'on' | 'in'
+        """
+        )
+        self.assertFalse(grammar2.is_flexible_chomsky_normal_form())
+        self.assertFalse(grammar2.is_chomsky_normal_form())
+        grammar2 = grammar2.chomsky_normal_form()
+        self.assertTrue(grammar2.is_flexible_chomsky_normal_form())
+        self.assertTrue(grammar2.is_chomsky_normal_form())
+
+    def test_complex(self):
+        grammar = nltk.data.load('grammars/large_grammars/atis.cfg')
+        self.assertFalse(grammar.is_flexible_chomsky_normal_form())
+        self.assertFalse(grammar.is_chomsky_normal_form())
+        grammar = grammar.chomsky_normal_form(flexible=True)
+        self.assertTrue(grammar.is_flexible_chomsky_normal_form())
+        self.assertFalse(grammar.is_chomsky_normal_form())