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feedback/diff_engine.py — difflib-based diff with change_ratio
Computes structured diffs between original and edited draft text.
Filters out trivially small edits (< 5% change) to avoid learning
from minor typo fixes.
"""
import difflib
from models import EditDiff
class DiffEngine:
"""Compute structured diffs between original and edited text."""
def compute(self, original: str, edited: str) -> EditDiff:
"""
Compute the diff between original and edited text.
Returns an EditDiff with additions, deletions, and change_ratio.
change_ratio ranges from 0.0 (identical) to 1.0 (completely different).
"""
orig_lines = original.splitlines()
edit_lines = edited.splitlines()
opcodes = difflib.SequenceMatcher(
None, orig_lines, edit_lines
).get_opcodes()
additions: list[str] = []
deletions: list[str] = []
for tag, i1, i2, j1, j2 in opcodes:
if tag == "insert":
additions.append("\n".join(edit_lines[j1:j2]))
elif tag == "delete":
deletions.append("\n".join(orig_lines[i1:i2]))
elif tag == "replace":
deletions.append("\n".join(orig_lines[i1:i2]))
additions.append("\n".join(edit_lines[j1:j2]))
# Character-level similarity ratio
change_ratio = 1.0 - difflib.SequenceMatcher(
None, original, edited
).ratio()
return EditDiff(
additions=additions,
deletions=deletions,
original=original,
edited=edited,
change_ratio=round(change_ratio, 3),
)
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