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gh-119105: difflib: improve recursion for degenerate cases #119131

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Merged
tim-one merged 10 commits into from
May 19, 2024
Merged

gh-119105: difflib: improve recursion for degenerate cases #119131

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9bb454c
difflib.py: fix recursion branching for degenerate cases
pulkin May 17, 2024
a159954
difflib.py: grammar
pulkin May 17, 2024
81b7dae
difflib.py: weights-free implementation
pulkin May 18, 2024
2184911
difflib.py: rm left-over
pulkin May 18, 2024
f9e3480
difflib.py: even simpler impl
pulkin May 19, 2024
b0be97f
📜🤖 Added by blurb_it.
blurb-it[bot] May 19, 2024
bea603e
difflib.py: add a desc
pulkin May 19, 2024
df83f50
📜🤖 Added by blurb_it.
blurb-it[bot] May 19, 2024
0953ede
news: attempt fix build
pulkin May 19, 2024
7237b48
difflib.py: NEWS message
pulkin May 19, 2024
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difflib.py: grammar
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@pulkin
pulkin authored May 17, 2024
commit a159954afc78d44ba18a172eb845fdc84cc894e1
8 changes: 4 additions & 4 deletions Lib/difflib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -917,13 +917,13 @@ def _fancy_replace(self, a, alo, ahi, b, blo, bhi):

max_len_a = max(map(len, a))
max_len_b = max(map(len, b))
# twice epsilon can be safely added to distinguish equal ratios
# given ratios are 2 * integer / (len_i + len_j)
# twice the epsilon can be safely added to distinguish otherwise
# equal ratios. given ratios are 2 * integer / (len_i + len_j)
# the smallest possible non-zero difference between two arbitrary
# ratios is no less than twice the epsilon
epsilon = 0.99 / (max_len_a + max_len_b) ** 2
# we use sub-epsilon weights to promote otherwise equal ratios
# that split sequences closer to their midpoints
# we use sub-epsilon weights to promote i, j that split the
# input range more equally.
# this way, we balance the recursion tree in degenerate cases

# search for the pair that matches best without being identical
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