@@ -44,13 +44,18 @@ diffs. For comparing directories and files, see also, the :mod:`filecmp` module.
4444 complicated way on how many elements the sequences have in common; best case
4545 time is linear.
4646
47- **Automatic junk heuristic: ** :class: `SequenceMatcher ` supports a heuristic that
48- automatically treats certain sequence items as junk. The heuristic counts how many
49- times each individual item appears in the sequence. If an item's duplicates (after
50- the first one) account for more than 1% of the sequence and the sequence is at least
51- 200 items long, this item is marked as "popular" and is treated as junk for
52- the purpose of sequence matching. This heuristic can be turned off by setting
53- the ``autojunk `` argument to ``False `` when creating the :class: `SequenceMatcher `.
47+ **Junk **: :class: `SequenceMatcher ` accepts an ``isjunk `` predicate and an
48+ ``autojunk `` flag. Items that are considered as junk will not be considered
49+ to find similar content blocks. This can produce better results for humans
50+ (typically breaking on whitespace) and faster (because it reduces the number
51+ of possible combinations). But it can also cause pathological cases where
52+ too many items considered junk cause an unexpectedly large (but correct)
53+ diff result.
54+ You should consider tuning them or turning them off depending on your data.
55+ Moreover, only the second sequence is inspected for junk. This causes the diff
56+ output to not be symmetrical.
57+ When ``autojunk=True ``, it will consider as junk the items that account for more
58+ than 1% of the sequence, if it is at least 200 items long.
5459
5560 .. versionchanged :: 3.2
5661 Added the *autojunk * parameter.
@@ -554,16 +559,6 @@ The :class:`SequenceMatcher` class has this constructor:
554559 to try :meth: `quick_ratio ` or :meth: `real_quick_ratio ` first to get an
555560 upper bound.
556561
557- .. note ::
558-
559- Caution: The result of a :meth: `ratio ` call may depend on the order of
560- the arguments. For instance::
561-
562- >>> SequenceMatcher(None, 'tide', 'diet').ratio()
563- 0.25
564- >>> SequenceMatcher(None, 'diet', 'tide').ratio()
565- 0.5
566-
567562
568563 .. method :: quick_ratio()
569564
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