Skip to content

[WIP] gh-132166: Add check in find_longest_match for checking if sequences are identical #132167

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 4 commits into
base: main
Choose a base branch
from
Open

[WIP] gh-132166: Add check in find_longest_match for checking if sequences are identical #132167

Show file tree
Hide file tree
Changes from 3 commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
fc53f9e
initial commit
jurgenwigg Apr 6, 2025
6fce1a0
📜🤖 Added by blurb_it.
blurb-it[bot] Apr 6, 2025
132e938
fixed news lint fail
jurgenwigg Apr 6, 2025
7a2f27b
Update difflib.py
jurgenwigg Apr 6, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
12 changes: 8 additions & 4 deletions Lib/difflib.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -361,10 +361,14 @@ def find_longest_match(self, alo=0, ahi=None, blo=0, bhi=None):
# the unique 'b's and then matching the first two 'a's.

a, b, b2j, isbjunk = self.a, self.b, self.b2j, self.bjunk.__contains__
if ahi is None:
ahi = len(a)
if bhi is None:
bhi = len(b)
ahi = ahi if ahi is not None else len(a)
bhi = bhi if bhi is not None else len(b)

# Check if both sequences are the same before executing rest of the
# method.
if a[alo:ahi] == b[blo:bhi]:
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Is this covered in tests? if not, please add a test, otherwise no need to add a large one.

return Match(alo, blo, len(a[alo:ahi]))

besti, bestj, bestsize = alo, blo, 0
# find longest junk-free match
# during an iteration of the loop, j2len[j] = length of longest
Expand Down
5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-04-06-17-31-44.gh-issue-132166.tbo9yR.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
Add checking if sequences ``a[alo:ahi]`` and ``b[blo:bhi]`` are the same on the
beginning of the method find_longest_match in SequenceMatcher. For identical
sequences there is no reason to run whole logic when simple check can be done.
Comment on lines +1 to +3
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This NEWS should be summarized. I suggest something like (assumiong that the method is documented, if not use a plain

Add a fast path in :meth:`SequenceMatcher.find_longest_match
<difflib.SequenceMatcher.find_longest_match>` to handle the
case when ``a[alo:ahi] == b[blo:bhi]``.

It appears to fix issue when comparing two slightly different strings ends up
with waiting forever for the result.
Comment on lines +4 to +5
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
It appears to fix issue when comparing two slightly different strings ends up
with waiting forever for the result.
It appears to fix issue when comparing two slightly different strings ends up
with waiting forever for the result.

We should be more confident here. Does it fix the issue or not? if so, let's say it. Otherwise, let's not give tentative conclusions.

Loading