cpython/Tools/build/generate_levenshtein_exampl...

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"""Generate 10,000 unique examples for the Levenshtein short-circuit tests."""
import argparse
from functools import lru_cache
import json
import os.path
from random import choices, randrange
# This should be in sync with Lib/traceback.py. It's not importing those values
# because this script is being executed by PYTHON_FOR_REGEN and not by the in-tree
# build of Python.
_MOVE_COST = 2
_CASE_COST = 1
def _substitution_cost(ch_a, ch_b):
if ch_a == ch_b:
return 0
if ch_a.lower() == ch_b.lower():
return _CASE_COST
return _MOVE_COST
@lru_cache(None)
def levenshtein(a, b):
if not a or not b:
return (len(a) + len(b)) * _MOVE_COST
option1 = levenshtein(a[:-1], b[:-1]) + _substitution_cost(a[-1], b[-1])
option2 = levenshtein(a[:-1], b) + _MOVE_COST
option3 = levenshtein(a, b[:-1]) + _MOVE_COST
return min(option1, option2, option3)
def main():
parser = argparse.ArgumentParser(description=__doc__)
parser.add_argument('output_path', metavar='FILE', type=str)
parser.add_argument('--overwrite', dest='overwrite', action='store_const',
const=True, default=False,
help='overwrite an existing test file')
args = parser.parse_args()
output_path = os.path.realpath(args.output_path)
if not args.overwrite and os.path.isfile(output_path):
print(f"{output_path} already exists, skipping regeneration.")
print(
"To force, add --overwrite to the invocation of this tool or"
" delete the existing file."
)
return
examples = set()
# Create a lot of non-empty examples, which should end up with a Gauss-like
# distribution for even costs (moves) and odd costs (case substitutions).
while len(examples) < 9990:
a = ''.join(choices("abcABC", k=randrange(1, 10)))
b = ''.join(choices("abcABC", k=randrange(1, 10)))
expected = levenshtein(a, b)
examples.add((a, b, expected))
# Create one empty case each for strings between 0 and 9 in length.
for i in range(10):
b = ''.join(choices("abcABC", k=i))
expected = levenshtein("", b)
examples.add(("", b, expected))
with open(output_path, "w") as f:
json.dump(sorted(examples), f, indent=2)
if __name__ == "__main__":
main()