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cpython/Misc/NEWS.d/next/Library/2024-05-24-04-05-37.gh-issu...

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gh-119105: Differ.compare is too slow [for degenerate cases] (#119492) ``_fancy_replace()`` is no longer recursive. and a single call does a worst-case linear number of ratio() computations instead of quadratic. This renders toothless a universe of pathological cases. Some inputs may produce different output, but that's rare, and I didn't find a case where the final diff appeared to be of materially worse quality. To the contrary, by refusing to even consider synching on lines "far apart", there was more easy-to-digest locality in the output.
2024-05-25 00:08:21 -03:00
``difflib``'s ``DIffer.compare()`` (and so also ``ndiff``) can no longer be provoked into cubic-time behavior, or into unbounded recursion, and should generally be faster in ordinary cases too. Results may change in some cases, although that should be rare. Correctness of diffs is not affected. Some similar lines far apart may be reported as deleting one and adding the other, where before they were displayed on adjacent output lines with markup showing the intraline differences.