venv/lib/python3.10/site-packages/nltk/test/unit/test_distance.py

from typing import Tuple

import pytest

from nltk.metrics.distance import edit_distance


class TestEditDistance:
    @pytest.mark.parametrize(
        "left,right,substitution_cost,expecteds",
        [
            # Allowing transpositions reduces the number of edits required.
            # with transpositions:
            # e.g. "abc" -T-> "cba" -D-> "ca": 2 steps
            #
            # without transpositions:
            # e.g. "abc" -D-> "ab" -D-> "a" -I-> "ca": 3 steps
            ("abc", "ca", 1, (2, 3)),
            ("abc", "ca", 5, (2, 3)),  # Doesn't *require* substitutions
            # Note, a substition_cost of higher than 2 doesn't make much
            # sense, as a deletion + insertion is identical, and always
            # costs 2.
            #
            #
            # Transpositions don't always reduce the number of edits required:
            # with or without transpositions:
            # e.g. "wants" -D-> "wats" -D-> "was" -I-> "wasp": 3 steps
            ("wants", "wasp", 1, (3, 3)),
            ("wants", "wasp", 5, (3, 3)),  # Doesn't *require* substitutions
            #
            #
            # Ought to have the same results with and without transpositions
            # with or without transpositions:
            # e.g. "rain" -S-> "sain" -S-> "shin" -I-> "shine": 3 steps
            # (but cost 5 if substitution_cost=2)
            ("rain", "shine", 1, (3, 3)),
            ("rain", "shine", 2, (5, 5)),  # Does *require* substitutions
            #
            #
            # Several potentially interesting typos
            # with transpositions:
            # e.g. "acbdef" -T-> "abcdef": 1 step
            #
            # without transpositions:
            # e.g. "acbdef" -D-> "abdef" -I-> "abcdef": 2 steps
            ("acbdef", "abcdef", 1, (1, 2)),
            ("acbdef", "abcdef", 2, (1, 2)),  # Doesn't *require* substitutions
            #
            #
            # with transpositions:
            # e.g. "lnaguaeg" -T-> "languaeg" -T-> "language": 2 steps
            #
            # without transpositions:
            # e.g. "lnaguaeg" -D-> "laguaeg" -I-> "languaeg" -D-> "languag" -I-> "language": 4 steps
            ("lnaguaeg", "language", 1, (2, 4)),
            ("lnaguaeg", "language", 2, (2, 4)),  # Doesn't *require* substitutions
            #
            #
            # with transpositions:
            # e.g. "lnaugage" -T-> "lanugage" -T-> "language": 2 steps
            #
            # without transpositions:
            # e.g. "lnaugage" -S-> "lnangage" -D-> "langage" -I-> "language": 3 steps
            # (but one substitution, so a cost of 4 if substition_cost = 2)
            ("lnaugage", "language", 1, (2, 3)),
            ("lnaugage", "language", 2, (2, 4)),
            # Does *require* substitutions if no transpositions
            #
            #
            # with transpositions:
            # e.g. "lngauage" -T-> "lnaguage" -T-> "language": 2 steps
            # without transpositions:
            # e.g. "lngauage" -I-> "lanaguage" -D-> "language": 2 steps
            ("lngauage", "language", 1, (2, 2)),
            ("lngauage", "language", 2, (2, 2)),  # Doesn't *require* substitutions
            #
            #
            # with or without transpositions:
            # e.g. "wants" -S-> "sants" -S-> "swnts" -S-> "swits" -S-> "swims" -D-> "swim": 5 steps
            #
            # with substitution_cost=2 and transpositions:
            # e.g. "wants" -T-> "santw" -D-> "sntw" -D-> "stw" -D-> "sw"
            # -I-> "swi" -I-> "swim": 6 steps
            #
            # with substitution_cost=2 and no transpositions:
            # e.g. "wants" -I-> "swants" -D-> "swant" -D-> "swan" -D-> "swa" -D-> "sw"
            # -I-> "swi" -I-> "swim": 7 steps
            ("wants", "swim", 1, (5, 5)),
            ("wants", "swim", 2, (6, 7)),
            #
            #
            # with or without transpositions:
            # e.g. "kitten" -S-> "sitten" -s-> "sittin" -I-> "sitting": 3 steps
            # (but cost 5 if substitution_cost=2)
            ("kitten", "sitting", 1, (3, 3)),
            ("kitten", "sitting", 2, (5, 5)),
            #
            # duplicated letter
            # e.g. "duplicated" -D-> "duplicated"
            ("duplicated", "duuplicated", 1, (1, 1)),
            ("duplicated", "duuplicated", 2, (1, 1)),
            ("very duplicated", "very duuplicateed", 2, (2, 2)),
        ],
    )
    def test_with_transpositions(
        self, left: str, right: str, substitution_cost: int, expecteds: Tuple[int, int]
    ):
        """
        Test `edit_distance` between two strings, given some `substitution_cost`,
        and whether transpositions are allowed.

        :param str left: First input string to `edit_distance`.
        :param str right: Second input string to `edit_distance`.
        :param int substitution_cost: The cost of a substitution action in `edit_distance`.
        :param Tuple[int, int] expecteds: A tuple of expected outputs, such that `expecteds[0]` is
            the expected output with `transpositions=True`, and `expecteds[1]` is
            the expected output with `transpositions=False`.
        """
        # Test the input strings in both orderings
        for s1, s2 in ((left, right), (right, left)):
            # zip with [True, False] to get the transpositions value
            for expected, transpositions in zip(expecteds, [True, False]):
                predicted = edit_distance(
                    s1,
                    s2,
                    substitution_cost=substitution_cost,
                    transpositions=transpositions,
                )
                assert predicted == expected