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# Natural Language Toolkit: Language Model Unit Tests
#
# Copyright (C) 2001-2023 NLTK Project
# Author: Ilia Kurenkov <[email protected]>
# URL: <https://www.nltk.org/>
# For license information, see LICENSE.TXT
import unittest
import pytest
from nltk import FreqDist
from nltk.lm import NgramCounter
from nltk.util import everygrams
class TestNgramCounter:
"""Tests for NgramCounter that only involve lookup, no modification."""
@classmethod
def setup_class(self):
text = [list("abcd"), list("egdbe")]
self.trigram_counter = NgramCounter(
everygrams(sent, max_len=3) for sent in text
)
self.bigram_counter = NgramCounter(everygrams(sent, max_len=2) for sent in text)
self.case = unittest.TestCase()
def test_N(self):
assert self.bigram_counter.N() == 16
assert self.trigram_counter.N() == 21
def test_counter_len_changes_with_lookup(self):
assert len(self.bigram_counter) == 2
self.bigram_counter[50]
assert len(self.bigram_counter) == 3
def test_ngram_order_access_unigrams(self):
assert self.bigram_counter[1] == self.bigram_counter.unigrams
def test_ngram_conditional_freqdist(self):
case = unittest.TestCase()
expected_trigram_contexts = [
("a", "b"),
("b", "c"),
("e", "g"),
("g", "d"),
("d", "b"),
]
expected_bigram_contexts = [("a",), ("b",), ("d",), ("e",), ("c",), ("g",)]
bigrams = self.trigram_counter[2]
trigrams = self.trigram_counter[3]
self.case.assertCountEqual(expected_bigram_contexts, bigrams.conditions())
self.case.assertCountEqual(expected_trigram_contexts, trigrams.conditions())
def test_bigram_counts_seen_ngrams(self):
assert self.bigram_counter[["a"]]["b"] == 1
assert self.bigram_counter[["b"]]["c"] == 1
def test_bigram_counts_unseen_ngrams(self):
assert self.bigram_counter[["b"]]["z"] == 0
def test_unigram_counts_seen_words(self):
assert self.bigram_counter["b"] == 2
def test_unigram_counts_completely_unseen_words(self):
assert self.bigram_counter["z"] == 0
class TestNgramCounterTraining:
@classmethod
def setup_class(self):
self.counter = NgramCounter()
self.case = unittest.TestCase()
@pytest.mark.parametrize("case", ["", [], None])
def test_empty_inputs(self, case):
test = NgramCounter(case)
assert 2 not in test
assert test[1] == FreqDist()
def test_train_on_unigrams(self):
words = list("abcd")
counter = NgramCounter([[(w,) for w in words]])
assert not counter[3]
assert not counter[2]
self.case.assertCountEqual(words, counter[1].keys())
def test_train_on_illegal_sentences(self):
str_sent = ["Check", "this", "out", "!"]
list_sent = [["Check", "this"], ["this", "out"], ["out", "!"]]
with pytest.raises(TypeError):
NgramCounter([str_sent])
with pytest.raises(TypeError):
NgramCounter([list_sent])
def test_train_on_bigrams(self):
bigram_sent = [("a", "b"), ("c", "d")]
counter = NgramCounter([bigram_sent])
assert not bool(counter[3])
def test_train_on_mix(self):
mixed_sent = [("a", "b"), ("c", "d"), ("e", "f", "g"), ("h",)]
counter = NgramCounter([mixed_sent])
unigrams = ["h"]
bigram_contexts = [("a",), ("c",)]
trigram_contexts = [("e", "f")]
self.case.assertCountEqual(unigrams, counter[1].keys())
self.case.assertCountEqual(bigram_contexts, counter[2].keys())
self.case.assertCountEqual(trigram_contexts, counter[3].keys())
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